An aldol approach to a building block corresponding to the C21–C26-part of FK506

Starting from D-tartrate 2 , the chiral aldehyde 10 was prepared in 8 steps. Key steps include the reductive opening of the p-methoxybenzyl acetal 4 and the elongation of the aldehyde 7 via Wittig and hydroboration reaction providing the alcohol 9 . Subsequent Evans aldol reaction provided compound 12 which corresponds to the C21–C26 part of the immunosuppressive FK506.     

A Simple and Efficient Access to New Functionalized 4‐Phenacylideneflavenes#

An innovative and efficient approach towards diversity‐oriented synthesis of 4‐phenacylideneflavenes has been developed from substituted salicylaldehydes and acetophenones using iodine under solvent‐free conditions. Both symmetrical and unsymmetrical functionalized 4‐phenacylideneflavenes were synthesized in good to excellent yields and their mechanism of formation is discussed.     

Access to 2‐Aminopyridines – Compounds of Great Biological and Chemical Significance

2‐Aminopyridines are key structural cores of bioactive natural products, medicinally important compounds, and organic materials and thus, extremely valuable synthetic targets. The few reported 6‐substituted 2‐aminopyridines and the lack of flexible, efficient and general applicable methods for their synthesis demonstrates the urgent need of new methods for their preparation. Reactions between 2,6‐dibromopyridine and primary or secondary, cyclic or acyclic, and aliphatic or aromatic amines were shown to selectively yield the respective 6‐bromopyridine‐2‐amines in very high yields which were successfully used as substrates for subsequent C C cross‐coupling reactions. The recently introduced dichloro‐bis[1‐(dicyclohexylphosphanyl)piperidine]palladium ( 1 ) was used as catalyst for the cross‐coupling of 6‐bromopyridine‐2‐amines with arylboronic acids, diaryl‐ and dialkylzinc reagents or olefins and hence, is also an excellent C C cross‐coupling catalyst for this type of substrate. Moreover, all the reaction protocols presented were in each of the catalyses uniformly applied. The scope of both the amination and the cross‐coupling reactions are well defined and allow one to simply adapt the reaction protocols directly to other amines and/or coupling partners and, thus, provide for the first time a very flexible and generally applicable reaction protocol to get access to 2‐aminopyridines.     

An Efficient New Pyrimidine Synthesis – a pathway to octupoles

The condensation of N,N,N′-tris(trimethylsilyl)-amidines ( 6 , 11 , 22 ) with vinamidinium salts ( 1 , 7 ) in the presence of potassium fluoride is the method of choice for the synthesis of pyrimidines ( 8 , 12 , 20 , 23 ). Octupoles comprising 1,3,5-benzene ( 8 ) and triphenylamine ( 12 , 20 ) derivatives can be prepared in high yields.     

New Intermediates and Dyes for Synthetic–polymer Fibres 4–(4–Methoxyanilino)–3–nitro–l, 8–naphthalimides

The synthesis of a series of 4–(4–methoxyanilinoj–3–nitro–1, 8–naphthalimides by condensation of amines with 4–(4–methoxyanilino)–3–nitronaphthalene–l, 8–dicarboxylic anhydride, and also by condensation of 4–halogeno–3–nitro–1, 8–naphthalimides with 4–methoxyaniline is described. They dye synthetic–polymer fibres, particularly polyesters, deep orange of excellent fastness properties. In presence of strong bases, e. g. 3–aminopropan–l–ol, the 4–arylamino group is replaced, giving a series of yellow dyes. A method is described for preparing the dyes without isolation of intermediate stages.     

A New Type of Stereoselectivity in Baeyer–Villiger Reactions: Access to E‐ and Z‐Olefins

A new concept for accessing configurationally defined trisubstituted olefins has been developed. Starting from a common ketone precursor of the type 4‐ethylidenecyclohexanone, Baeyer–Villiger monooxygenases are employed as catalysts in diastereoselective Baeyer–Villiger reactions leading to the corresponding E‐ or Z‐configurated lactones. Wild‐type cyclohexanone monooxygenase (CHMO) as catalyst delivers the E‐isomers and a directed evolution mutant the opposite Z‐isomers. Subsequent transition metal‐catalyzed chemical transformations of a key product containing a vinyl bromide moiety provide a variety of different trisubstituted E‐ or Z‐olefins. A model based on QM/MM sheds light on the origin of this unusual type of diastereoselectivity. In contrast to this biocatalytic approach, traditional Baeyer–Villiger reagents such as m‐CPBA fail to show any selectivity, 1:1 mixtures of E‐ and Z‐olefins being formed.     

Preparation of poly(dimethylsiloxane)–polypeptide block copolymers

Block copolymers composed of poly(dimethylsiloxane) segments linked to polypeptide have been synthesized by reacting primary amine-terminated silicone with N-carboxy anhydrides of amino acids. The amine-terminated silicone was prepared by reacting “living” polysilanolate with γ-aminopropyltriethoxysilane. The block copolymers prepared consisted of segments of poly(DL-phenylalanine) or poly(γ-benzyl-L -glutamate). The block copolymers were purified by extraction with solvents which are selective for the homopolymers. Analysis of the products was accomplished by hydrolysis of the polypeptide segments, infrared spectra, gel permeation chromatography, and elemental analysis. The content of the copolymers ranged from 50 to 87% polypeptide.     

Carbonylative Addition of Arylboronic Acids to Terminal Alkynes: A New Catalytic Access to α,β‐Unsaturated Ketones

The carbonylative addition of arylboronic acids to terminal alkynes under mild conditions affords (E)‐α,β‐unsaturated ketones with good yields. The reaction was achieved with chloro(1,5‐cyclooctadiene)rhodium(I) dimer or chlorodicarbonylrhodium(I) dimer as catalytic precursor without additional phosphine as their use inhibits the reaction. Experiments using deuterated 1‐hexyne discarded the possibility of a rhodium‐vinylidene intermediate, thus a catalytic cycle involving a 1,2‐insertion of the terminal alkyne in a rhodium‐acyl bond is proposed. This new reaction represents the first example of the hydroacylation of terminal alkynes involving rhodium‐acyl reagents generated under CO pressure and promises a wide field of interest.     

A New Metal‐Free Access to Vitamin K3

2‐Methylnaphthalene is oxidized in about 80 % yield with 7–9/1 regioselectivity to 2‐methyl‐1,4‐naphthoquinone by hydrogen peroxide with a strong mineral acid as the catalyst. No (transition) metal catalyst is required for this transformation.     

Direct Access to Medium‐Chain α,ω‐Dicarboxylic Acids by Using a Baeyer–Villiger Monooxygenase of Abnormal Regioselectivity

Baeyer–Villiger monooxygenases (BVMOs) are versatile biocatalysts in organic synthesis that can generate esters or lactones by inserting a single oxygen atom adjacent to a carbonyl moiety. The regioselectivity of BVMOs is essential in determining the ratio of two regioisomers for converting asymmetric ketones. Herein, we report a novel BVMO from Pseudomonas aeruginosa (PaBVMO); this has been exploited for the direct synthesis of medium‐chain α,ω‐dicarboxylic acids through a Baeyer–Villiger oxidation–hydrolysis cascade. PaBVMO displayed the highest abnormal regioselectivity toward a variety of long‐chain aliphatic keto acids (C₁₆–C₂₀) to date, affording dicarboxylic monoesters with a ratio of up to 95 %. Upon chemical hydrolysis, α,ω‐dicarboxylic acids and fatty alcohols are readily obtained without further treatment; this significantly reduces the synthetic steps of α,ω‐dicarboxylic acids from renewable oils and fats.     

Undecylenic acid: A valuable renewable building block on route to Tyromycin A derivatives

A key intermediate for the synthesis of Tyromycin A, a C‐20 tetrachlorodicarboxylic acid, was produced in six steps starting with the dimerization of methyl 10‐undecenoate which was obtained from a renewable resource, e.g. castor oil. The acyloin condensation product was then oxidized, transformed to the diene, followed by ozonization, chlorination and finally oxidation to the corresponding tetrachlorodicarboxylic acid.     

New block copolymers of α-amino acids

Triblock cepolypeptides of γ-benzyl-L-glutamate and L-leucine or L-valine of high molecular weight have been prepared. The solid state structure of the block copolymers cast from preferential solvents has been compared with that of random copolymers of similar composition as well as the appropriate homopolymers. Infrared and solid state circular dichroism measurements indicate that the γ-benzyl-L-glutamate and L-leucine blocks assume an α-helical conformation and L-valine blocks a β-sheet structure. The WAXD patterns of the block copolymers show overlapping reflections characteristic of the individual homopolymers. Further evidence for a phase separated morphology is provided by dynamic mechanical spectroscopy.     

4–Hydroxy–3–arylamino–l, 8–naphthalimides and 3–(and 4–) hydroxy–2–(and 5–) arylamino–7H–bcnzimidazo–(2, l–a)benz(d,e)isoquinolin–7–ones. Red dyes for synthetic–polymer fibres

4–Hydroxy–1, 8–naphthalimides and the isomer mixtures of'3–and 4–hydroxy–7 H–benzimidazo–(2, l–a)–benz(d, e)–isoquinolin–7–ones were coupled with diazotised arylamines to yield orange–red to bluish–red dyes having good coloration properties and excellent fastness to light on polyester fibres. Structure–property relationships in the dyes are discussed with respect to the nature of the substituents in the imide, imidazole and arylazo moieties.     

Poly(α-methylstyrene)–poly(dimethylsiloxane) block copolymers

Block copolymers were synthesized by the condensation of dihydroxyl-terminated poly-(α-methylstyrene) oligomers and bisdimethylamino-terminated poly(dimethylsiloxane) oligomers. Manipulation of block molecular weight produced copolymers ranging in composition from 21% to 73% poly(dimethylsiloxane). Compression moldablity was found to be good. Physical properties were dependent upon siloxane content, varying from high modulus, low elongation to low modulus, high elongation materials. High siloxane-content compositions exhibited elastomeric properties due to the two-phase morphology of these systems. Glass transition temperatures were observed as low as ?120°C for the poly(dimethylsiloxane) block and as high as + 140°C for the poly(α-methylstyrene) block. Even higher poly(α-methylstyrene) transition temperatures may be possible by using higher molecular weight oligomers.     

Crystallographic study of two monoazo disperse dyes with a D–π–A system

Two azo disperse dyes, 2,6‐dichoro‐4‐nitro‐4′,4′‐N‐cyanoethyl‐N‐benzyl‐azobenzene ( D1 ) and 3‐(3‐methyl‐4‐N‐ethyl‐N‐benzyl‐phenyldiazenyl)‐5‐nitro‐2,1‐benzisothiazole ( D2 ), were synthesised and characterised. The crystal morphologies and single crystal structures were measured. The various packing and supramolecular interactions were described. D1 formed stellate crystals. The two benzene rings bilateral to the azo unit were not coplanar. Their dihedral angle was 75.72°. They were linked by the azo unit and were twisted. The coupling‐component N‐substituted benzyl and benzene rings were not coplanar. The chemical structure was not the typical azo structure. A dimeric packing mode was formed between adjacent molecules in a head‐to‐head and tail‐to‐tail manner. One molecule was inserted between two dimeric molecules in a head‐to‐tail manner. D2 formed globe crystals. The isothiazole and benzene rings of the azo unit were coplanar, with the typical π–π conjugated structure. The benzene rings of the azo unit and the coupling‐component N‐substituted benzyl were vertical. Their torsion angle was 179.9°.