Host/guest complex of Me-β-CD/2,2-dimethoxy-2-phenyl acetophenone for initiation of aqueous photopolymerization: Kinetics and mechanism

Methylated-β-cyclodextrin (Me-β-CD) was used to complex the photoinitiator, 2,2-dimethoxy-2-phenyl acetophenone (DMPA), yielding a water-soluble host/guest complex. The comparative studies demonstrated that the Me-β-CD complexed DMPA exhibited a high photoreactivity identical to the uncomplexed DMPA, while the CD complex obviously influenced the products of primary photolysis of DMPA and the photopolymerization kinetics due to the steric effect of CD on the subsequent initiation reactions. The photopolymerization rate of acrylamide can be described by the equation: R_p=K[2a]^0.62[M]^1.37[I]^0.5[Me-β-CD]⁰. The mechanism of polymerization was also discussed.     

Efficiency of 2,2‐dimethoxy‐2‐phenylacetophenone for the photopolymerization of methacrylate monomers in thick sections

The efficiency of 2,2‐Dimethoxy‐2‐phenylacetophenone (DMPA) for the photopolymerization of methacrylate monomers in thick sections was assessed. DMPA is an efficient photoinitiator for thick sections (≈2 mm) because a fast reaction and high conversions are obtained with concentrations as low as 0.25 wt % DMPA. The polymerization rate increased when the DMPA content increased from 0.125 wt % to 0.25 wt %. However, the conversion versus irradiation time profiles in resins containing 0.25 wt % or 0.5 wt % DMPA were similar. This is attributed to the screening effect caused by excessive levels of DMPA. In addition, the consumption of DMPA under UV irradiation was accompanied by the appearance of light absorbing photoproducts. Because the absorbing species nearest to the light source absorb part of it, the light fails to reach the deeper layers of the sample. The overall effect of light screening is a reduced photoinitiation rate and double bond conversion along the irradiation path. This effect was compensated by the use of irradiation sources of higher intensity; which increased the initiation rate by increasing the production of primary radicals. DMPA is colorless and it does not require the presence of amine as coinitiator. These properties make DMPA attractive as photoinitiator of dental composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and properties of hydrogels of poly(acrylic‐co‐acroloyl β‐cyclodextrin)

Novel acrylic monomers (β‐CD‐A and β‐CD‐6‐EA) containing β‐cyclodextrin (β‐CD) with different extent of substitution were prepared by using dicyclohexylcarbodiimide (DCC) as a condensation agent at room temperature. Two kinds of functional hydrogels were also synthesized by copolymerization of β‐CD‐A and β‐CD‐6‐EA with acrylic acid (AAc) using a redox initiator system in aqueous solution. The nuclear magnetic resonance (¹H NMR), infrared spectroscopy (IR), thermogravimetric analysis (TGA) were employed to character the molecular structures of β‐CD modified monomers and their copolymers. The swelling experiments indicate that the hydrogels with different equilibrium swelling ratio (ESR) possess obvious pH‐sensitivity and distinct dynamic swelling behavior. Using an anti‐cancer drug, chlorambucil (CHL), able to form complexes with β‐CD in water, as a model compound, the controlled drug release behaviors of these hydrogels were investigated. The release behavior of CHL from two kinds of hydrogels synthesized reveals that the release rate of CHL can be effectively controlled by pH values, cross‐linking density, and β‐CD content. In addition, it is found that the β‐CD with the proper frame and concentration can increase release efficiency of CHL from the hydrogels. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Monomer conversion in a light‐cured dental resin containing 1‐phenyl‐1,2‐ propanedione photosensitizer

The efficiency of 1‐phenyl‐1,2‐propanedione (PPD) photosensitizer for the photopolymerization of a dental resin based on 2,2‐bis[4‐(2‐hydroxy‐3‐methacryloxyprop‐1‐oxy)phenyl]propane/triethylene glycol dimethacrylate was assessed. Experimental formulations containing PPD or/and camphorquinone (CQ) in combination with dimethylaminoethyl methacrylate (DMAEMA), ethyl‐4‐dimethylaminobenzoate (EDMAB), 4‐(N,N‐dimethylamino)phenethyl alcohol (DMPOH) and N,N‐3,5‐tetramethylaniline (TMA) at different concentrations were studied. The photopolymerization was carried out by means of a commercial light‐emitting diode (LED) curing unit. Near‐infrared spectroscopy was used to follow the consumption of double bonds versus irradiation time. No significant differences in the conversion values among formulations prepared with PPD in combination with DMAEMA, DMPOH and TMA were found. In contrast, the conversion was markedly increased by the presence of EDMAB. At low concentrations of photosensitizer, when used in combination with DMAEMA and EDMAB, PPD resulted in a final conversion equivalent to CQ. However, when DMPOH and TMA were used, PPD was found to be less efficient than CQ. In addition, at high photoinitiator concentration, the effectiveness of PPD was less than that of CQ independently of the co‐initiator used. The replacement of some CQ by an equivalent amount of PPD resulted in similar final monomer conversion as formulations having the same amount of CQ alone. The LED light source employed emitted in the wavelength range 410–490 nm with a peak around 470 nm, whereas the maximum molar absorbance of PPD was in the UV region. However, the small overlap of the spectral distribution of the LED curing lamp and the PPD absorption spectrum was compensated by the large extinction coefficient of PPD. Copyright © 2007 Society of Chemical Industry     

Copolymers of acrylic acid with N‐vinylpyrrolidinone and 2‐hydroxyethyl methacrylate as pH‐responsive hydrogels synthesized through a photoinitiator‐free photopolymerization technique

pH‐sensitive hydrogels for biomedical applications were synthesized using a photoinitiator‐free technique involving the initiation of photopolymerization by donor/acceptor pairs. The differential photocalorimetric technique indicated a high polymerization rate for the N‐vinylpyrrolidinone (NVP, donor)/acrylic acid (AA, acceptor) pair at a 1:1 molar ratio. However, photopolymerization of larger quantities of these monomers (1:1 molar ratio) produced a water‐soluble polymer. Nevertheless, an anionic hydrogel was successfully formed when a small quantity of 2‐hydroxyethyl methacrylate (HEMA) was included in the NVP/AA formulation. A mixture of HEMA and AA, although both are classified as acceptors, photopolymerized to produce a copolymer which functioned as an anionic hydrogel. The swelling and drug release of these hydrogels were investigated in acidic, neutral and basic pH environments. Their biocompatibility with HaCaT human epidermal keratinocyte cells was tested and a positive cell growth as evidenced by the 3‐[4,5‐dimethylthiazol‐2‐yl]‐2,5‐diphenyl tetrazolium bromide (MTT) cell proliferation assay indicated that these hydrogels have no toxic effect on HaCaT. Copyright © 2006 Society of Chemical Industry     

A water-soluble supramolecular structured photosensitive initiation system: Me-β-CD complex of xanthene dye/aryliodonium salt

A water-soluble supramolecular structured photosensitive initiator (SSPI) was developed by the supramolecular self-assembling between the photosensitizer (xanthene dye) and the initiator (Complex A). The structure of SSPI was characterized by static and dynamic fluorescence quenching method. The photolysis properties of SSPI in the film were evaluated. The photopolymerization of AM and bis-AM in the film using the SSPI as the photoinitiator was also carried out. The results indicated that the SSPI formation played an important role in the photolysis and photopolymerization process. The SSPI was an efficient water-soluble photosensitive initiator.     

Diaryl‐Substituted Azolylthioacetamides: Inhibitor Discovery of New Delhi Metallo‐β‐Lactamase‐1 (NDM‐1)

The emergence and spread of antibiotic‐resistant pathogens is a global public health problem. Metallo‐β‐lactamases (MβLs) such as New Delhi MβL‐1 (NDM‐1) are principle contributors to the emergence of resistance because of their ability to hydrolyze almost all known β‐lactam antibiotics including penicillins, cephalosporins, and carbapenems. A clinical inhibitor of MBLs has not yet been found. In this study we developed eighteen new diaryl‐substituted azolylthioacetamides and found all of them to be inhibitors of the MβL L1 from Stenotrophomonas maltophilia (K_i<2 μM ), thirteen to be mixed inhibitors of NDM‐1 (K_i<7 μM ), and four to be broad‐spectrum inhibitors of all four tested MβLs CcrA from Bacteroides fragilis, NDM‐1 and ImiS from Aeromonas veronii, and L1 (K_i<52 μM ), which are representative of the B1a, B1b, B2, and B3 subclasses, respectively. Docking studies revealed that the azolylthioacetamides, which have the broadest inhibitory activity, coordinate to the Zn^II ion(s) preferentially via the triazole moiety, while other moieties interact mostly with the conserved active site residues Lys224 (CcrA, NDM‐1, and ImiS) or Ser221 (L1).     

Click‐coupling of anthraquinone dyes with β‐cyclodextrin: formation of polymeric superstructures

Two novel cyclodextrin‐modified anthraquinone dyes were synthesized and investigated for their complexation behaviour and formation of superstructures. Therefore, 1‐fluoro‐4‐N‐(propargylamino)anthraquinone and 1,4‐bis(propargyloxy)anthraquinone were prepared via nucleophilic aromatic displacement and subsequently covalently ‘click‐coupled’ in a copper(I)‐catalysed azide–alkyne cycloaddition with β‐cyclodextrin monoazide. Both the propargyl‐modified precursor and the click‐coupled anthraquinone dyes were evaluated as hosts and guests, respectively, in β‐cyclodextrin interactions. The anthraquinone dye bearing two cyclodextrins, 1,4‐bis((1‐β‐cyclodextrin‐1H‐1,2,3‐triazol‐5‐yl)methoxy)anthraquinone, enables the reversible formation of supramolecular crosslinked poly[(N,N‐dimethyl acrylamide)‐co‐(N‐(ferrocenoylmethyl)acrylamide)] ( 11 ), whereas the monofunctionalized compound 1‐fluoro‐4‐(((1‐β‐cyclodextrin‐1H‐1,2,3‐triazol‐5‐yl)methyl)amino)anthraquinone can be supramolecularly linked to 11 resulting in coloured polymers. These features of β‐cyclodextrin‐linked anthraquinone dyes can be verified with either ¹H ¹H NMR rotating frame nuclear Overhauser effect spectroscopy or the naked eye. © 2016 Society of Chemical Industry     

Synthesis of β‐cyclodextrin‐based dendrimer as a novel encapsulation agent

The aim was the fabrication of glycodendrimer encapsulation agents with high proportions of cyclodextrins (CDs) to maintain the biocompatibility properties, as well as to notably improve their ability to load various suitably sized drugs. The novel glycodendrimers contained β‐CD in both core and branches, namely β‐cyclodextrin‐based dendrimer (CD‐dendrimer) prepared through a straightforward procedure using S_N2 displacement to attach multivalent β‐CDs together. The desired CD‐dendrimer was synthesized in three steps: (i) reaction of β‐CD with p‐toluenesulfonyl chloride and/or iodine to afford C‐6 mono‐ and/or per‐β‐CD derivative; (ii) reaction of the β‐CD precursors with ethylenediamine to give C‐6 mono‐ and/or per‐amino‐β‐CD derivative; and (iii) S_N2 displacement of β‐CD electrophilic derivative with β‐CD nucleophilic derivative in dimethylsulfoxide to provide the CD‐dendrimer. Then, the encapsulation behaviour of the CD‐dendrimer was examined using naproxen and naltrexone as the guest molecules. The structure of the designed CD‐dendrimer allowed two types of possible sites for encapsulation of the guest: in cavities of the dendritic structure and in hydrophobic cavities of CDs. © 2013 Society of Chemical Industry     

DNA adsorption on a poly‐L‐lysine‐immobilized poly(2‐hydroxyethyl methacrylate) membrane

The DNA adsorption properties of poly‐L ‐lysine‐immobilized poly(2‐hydroxyethyl methacrylate) (pHEMA) membrane were investigated. The pHEMA membrane was prepared by UV‐initiated photopolymerization and activated with epichlorohydrin. Poly‐L ‐lysine was then immobilized on the activated pHEMA membrane by covalent bonding, via a direct chemical reaction between the amino group of poly‐L ‐lysine and the epoxy group of pHEMA. The poly‐L ‐lysine content of the membrane was determined as 1537 mg m^?2. The poly‐L ‐lysine‐immobilized membrane was utilized as an adsorbent in DNA adsorption experiments. The maximum adsorption of DNA on the poly‐L ‐lysine‐immobilized pHEMA membrane was observed at 4 °C from phosphate‐buffered salt solution (pH 7.4, 0.1 M; NaCl 0.5 M) containing different amounts of DNA. The non‐specific adsorption of DNA on the plain pHEMA membrane was low (about 263 mg m^?2). Higher DNA adsorption values (up to 5849 mg m^?2) were obtained in which the poly‐L ‐lysine‐immobilized pHEMA membrane was used. Copyright © 2003 Society of Chemical Industry     

Preparation and antidehydration of interpenetrating polymer network hydrogels based on 2‐hydroxyethyl methacrylate and N‐vinyl‐2‐pyrrolidone

This work reports the preparation of 2‐hydroxyethyl methacrylate (HEMA)/N‐vinyl‐2‐pyrrolidone (NVP) interpenetrating polymer network (IPN) hydrogels by UV‐initiated polymerization in the presence of free radical photoinitiator Darocur 1173 and cationic photoinitiator 4,4′‐dimethyl diphenyl iodonium hexafluorophosphate. The polymerization mechanism was investigated by the formation of gel network. The structure and morphology of the HEMA/NVP IPN hydrogels were characterized by fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). The results showed that the IPN gels exhibited homogeneous morphology. The dehydration rates of HEMA/NVP IPN hydrogels were examined by the gravimetric method. The results revealed that the hydrogels had a significant improvement of antidehydration ability in comparison with poly(2‐hydroxyethyl methacrylate)(PHEMA) hydrogel embedded physically with poly(N‐vinyl‐2‐pyrrolidone)(PVP). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Photoinitiating behavior of bifunctional photoinitiator containing α‐hydroxyalkylphenone group on free‐radical polymerization

Photoinitiating behaviors of bis[4‐(2‐hydroxy‐isopropionyl)]ether photoinitiator on free‐radical polymerization have been investigated. The kinetics of photopolymerization initiated by the photoinitiator was studied by means of differential photocalorimetry. The bifunctional photoinitiator showed comparative performance with those commercial photoinitiators with monofunctional chromophoric group. The effect of UV intensity on the polymerization rate was investigated, and the value of exponential factor was found to be 0.5 at the beginning of polymerization, suggesting that the photopolymerization initiated by bis[4‐(2‐hydroxy‐isopropionyl)]ether followed biradical termination mechanism. Photosensitizer triethylamine improves the initiating efficiency while oxygen is shown to restrict polymerization in this system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5297–5302, 2006     

Synthesis and characterization of isocyanic acid,m‐phenylenediiso‐propylidene based poly(urethane‐urea) dispersions containing different amount of 2,2‐Bis(hydroxyl methyl)propionic acid

Isocyanic acid, m‐phenylenediiso‐propylidene (m‐TMXDI)‐based anionic poly(urethane‐urea) dispersions were prepared by the prepolymer mixing process. The equivalent ratio of NCO/OH was kept constant at 1.8, while 2,2‐bis(hydroxyl methyl) propionic acid (DMPA) used was varied from 3 to 10 wt %. The colloidal stability of poly(urethane‐urea) dispersions arose entirely from the presence of ionized carboxylic acid groups. The chemical structure of poly(urethane‐urea) dispersions with various amount of DMPA were identified by FTIR and ¹³C NMR analysis. The test results showed that the hydrophilicity of poly(urethane‐urea) dispersions were increased with increase in DMPA content. The degree of chain extension was much lower than the values predicted theoretically due to the side reaction of a small amount of hydrophilic isocyanate‐terminated prepolymer with water. The average particle size of poly(urethane‐urea) dispersions were decreased with an increase in DMPA content, and this lead to an increase in viscosity. Also, the thermal degradation behavior were measured and was shown that the initial degradation temperature shifted to lower temperature with an increase in DMPA content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5737–5746, 2006     

Synthesis,Crystal Structure,and Thermal Behaviors of 3‐Nitro‐1,5‐bis(4,4′‐dimethylazide)‐1,2,3‐triazolyl‐3‐azapentane (NDTAP)

The energetic material, 3‐nitro‐1,5‐bis(4,4′‐dimethyl azide)‐1,2,3‐triazolyl‐3‐azapentane (NDTAP), was firstly synthesized by means of Click Chemistry using 1,5‐diazido‐3‐nitrazapentane as main material. The structure of NDTAP was confirmed by IR, ¹H NMR, and ¹³C NMR spectroscopy; mass spectrometry, and elemental analysis. The crystal structure of NDTAP was determined by X‐ray diffraction. It belongs to monoclinic system, space group C2/c with crystal parameters a=1.7285(8) nm, b=0.6061(3) nm, c=1.6712(8) nm, β=104.846(8)°, V=1.6924(13) nm³, Z=8, μ=0.109 mm⁻¹, F(000)=752, and D_c=1.422 g cm⁻³. The thermal behavior and non‐isothermal decomposition kinetics of NDTAP were studied with DSC and TG‐DTG methods. The self‐accelerating decomposition temperature and critical temperature of thermal explosion are 195.5 and 208.2 °C, respectively. NDTAP presents good thermal stability and is insensitive.     

Synthesis of a novel linear water‐soluble β‐cyclodextrin polymer

A novel linear water‐soluble β‐cyclodextrin polymer has been prepared by grafting β‐cyclodextrin on poly[(methyl vinyl ether)‐alt‐(maleic anhydride)]. First, lithium hydride was used to obtain the mono‐alkoxide β‐CD. Grafting of β‐CD derivatives to the polymer backbone was then carried out by an esterification method. Using this method, polymers containing various amounts of β‐CD were synthesized. The resulting grafted polymers were characterized by two complementary methods, ¹H NMR and IR spectroscopy. The first was used to calculate the degree of substitution for the low amounts of β‐CD. The second method was very useful to evaluate the degree of substitution and the molar ratio of CD especially for high amounts of grafting. Our results indicate good agreement between both methods for intermediate rates. Copyright © 2004 Society of Chemical Industry     

Behavior of α‐ and β‐cyclodextrin‐encapsulated allyl isothiocyanate as slow‐release additives in polylactide‐co‐polycaprolactone films

The natural antibacterial agent allyl isothiocyanate (AITC) encapsulated in either α‐ or β‐cyclodextrin (CD) has previously been evaluated as a slow‐release additive in polylactide‐co‐polycaprolactone (PLA–PCL) films designed for use in cheese packaging. In the research described in this article, thermogravimetric analysis (TGA) and thermogravimetric analysis in tandem with mass spectrometry (TGA–MS) were used to explore the thermal properties of CD‐encapsulated AITC complexes as well as those of PLA–PCL films containing these complexes. To our knowledge, this is the first reported application of the TGA–MS technique to explore the thermal stability of CD‐entrapped AITC and the first study to report differences in thermal stability of AITC in α‐and β‐CD cavities in the solid state. Observed differences in the thermal degradation profile of films containing the CD complexes can be explained if AITC binds more strongly to β‐CD than to α‐CD. This hypothesis has been reinforced by gas chromatography (GC) and high performance liquid chromatography (HPLC) studies, the results of which suggest that a new covalently bound AITC–CD complex may be formed when incorporating the β‐CD complex of AITC in PLA–PCL films but not when incorporating the α‐CD complex of AITC. This finding means that the α‐CD complex of AITC would be preferred in situations where adequate long‐term controlled release of AITC from polymer films is required, as for example in the case of active packaging applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis and biological activity of medium molecular weight polymers containing 3,6‐endo‐methylene‐1,2,3,6‐tetrahydrophthalimidobutanoyl‐5‐fluorouracil

A new monomer, 3,6‐endo‐methylene‐1,2,3,6‐tetrahydrophthalimidobutanoyl‐5‐fluorouracil (ETBFU), was synthesized by reaction of 3,6‐endo‐methylene‐1,2,3,6‐tetrahydrophthalimidobutanoyl chloride and 5‐fluorouracil. The homopolymer of ETBFU and its copolymers with acrylic acid (AA) or vinyl acetate (VAc) were prepared by photopolymerization using 2,2‐dimethoxy‐2‐phenylacetophenone as an initiator at 25 °C. The synthesized ETBFU and its polymers were identified by FTIR, ¹H NMR and ¹³C NMR spectroscopies. The ETBFU content in poly(ETBFU‐co‐AA) and poly(ETBFU‐co‐VAc) was 43 and 14 mol%, respectively. The apparent number‐average molecular weight (M_n) of the polymers determined by GPC ranged from 8400 to 11 300. The in vitro cytotoxicity of the samples against mouse mammary carcinoma (FM3A), mouse leukaemia (P388), and human histiocytic lymphoma (U937) cancer cell lines decreased in the order 5‐FU ≥ ETBFU > poly(ETBFU) > poly(ETBFU‐co‐AA) > poly(ETBFU‐co‐VAc). The in vivo antitumour activity of the polymers against Balb/C mice bearing sarcoma 180 tumour cells was greater than that of 5‐fluorouracil at all doses tested. © 2000 Society of Chemical Industry     

Effect of N‐phenylmaleimide on a novel chemically bonded polymerizable photoinitiator comprising the structure of planar N‐phenylmaleimide and benzophenone for photopolymerization

A novel chemically bonded polymerizable photoinitiator 4‐[(4‐maleimido)phenoxy]benzophenone (MPBP) comprising the structure of planar N‐phenylmaleimide (NPMI) and benzophenone (BP), compared with the physical mixtures of NPMI/BP or NPMI/4‐hydroxybenzophenone, was investigated to disclose the mutual influence between NPMI and BP. A BP derivative, 4‐phenoxylbenzophenone, was selected as the model compound. Electron spin resonance spectra of such photoredox systems indicated MPBP and BP possess the same initiation mechanism. The large red‐shifted π–π* absorption of MPBP should be because of the phenoxyl group in MPBP but not the maleimide group. The photopolymerization of methyl methacrylate (MMA) and 1,6‐hexanediol diacrylate (HDDA) initiated by those systems, using the unsaturated tertiary amine N,N‐dimethylaminoethyl methacrylate (DMAEMA) as the coinitiator (H donor), was studied through dilatometry and photo‐differential scanning calorimetry. The results showed that MPBP was more efficient for the photopolymerization of MMA and HDDA than its physical mixture counterpart. The high efficiency of MPBP may be mainly because of the interaction between NPMI and BP group but not the phenoxyl group alone. A certain amount of NPMI can accelerate the photopolymerization when added to the formulations, but too much NPMI will eventually decrease the photoefficiency. Copyright © 2006 Society of Chemical Industry     

Photopatterning and degradation study of dextran‐glycidyl methacrylate hydrogels

An approach to synthesizing photopatternable enzymatic degradable dextran hydrogel is presented. The glycidyl methacrylate derivatized dextran (Dex‐GMA) was first prepared by reacting dextran with glycidyl methacrylate at 45°C with grafting efficiency of 10%. The degree of substitution (DS) was confirmed by ¹H‐NMR. Next, Dex‐GMA hydrogels were prepared by crosslinking in the presence of a crosslinker: N,N′‐ methylene‐bisacrylamide (NMBA), and a photoinitiator: 2,2′‐dimethoxy‐2‐phenyl acetophenone (DMPA) in dimethyl sulfoxide (DMSO) solution. Further, the Dex‐GMA hydrogels were photopatterned using liquid‐phase photopolymerization (LP³) technique. The structure size ranged from 5 mm to 300 μm and three different shapes of structures‐ ‐ —round, square, and star‐ ‐ —were demonstrated. The patterned Dex‐GMA hydrogel structures not only exhibited mechanical robustness but also biodegradability. The dextranase‐catalyzed degradation of Dex‐GMA hydrogels with different DS was investigated at 37°C. The morphology of the degraded Dex‐GMA hydrogels determined by SEM revealed the degree of enzymatic degradation due to dextranase. The Dex‐GMA hydrogel was fully degraded by dextranase with concentration of 2 U/ml in 5 days. The Dex‐GMA hydrogel also showed the ability to be readily integrated with microfluidics. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Improved conversion of 6‐endo‐tosyloxybicyclo[2.2.2]octan‐2‐ones into 6‐exo‐acetoxy and 6‐exo‐benzoyloxybicyclo[2.2.2]octan‐2‐ones

The reaction conditions for the conversion of 6‐endo‐tosyloxybicyclo[2.2.2]octan‐2‐one ( 7b ) into 6‐exo‐acetoxy ( 8b ) and 6‐exo‐benzoyloxybicyclo[2.2.2]octan‐2‐one ( 8a ), respectively, were improved. Thus known 6‐endo‐tosyloxy‐bicyclo[2.2.2]octan‐2‐ones (+)‐(1RS,6SR,8SR,11RS)‐11‐[(4‐toluenesulfonyl)oxy]tricyclo[6.2.2.0^1,6]dodecan‐9‐one ( 1a ), 13‐methyl‐15‐oxo‐9β,13b‐ethano‐9β‐podocarpan‐12β‐yl‐4‐toluenesulfonate ( 3a ), and methyl (13R)‐16‐oxo‐13‐[(4‐tolylsulfonyl)oxy]‐17‐noratisan‐18‐oate ( 5 ), were converted,in comparable yields, as previously recorded, but much shorter times, into (+)‐(1RS,6SR,8SR,11SR)‐11‐(benzoyloxy) tricyclo[6.2.2.0^1,6]dodecan‐9‐one ( 2 ), 13‐methyl‐15‐oxo‐9β,13β‐ethano‐9β‐podocarpan‐12α‐yl benzoate ( 4 ), and methyl (13S)‐13‐(benzoyloxy)‐16‐oxo‐17‐noratisan‐18‐oate ( 6 ), respectively.