A practical and environmentally friendly strategy for generating alkoxycarbonyl radicals from readily available carbazates under metal‐free conditions has been developed. In the presence of tetrabutylammonium iodide and tert‐butyl hydroperoxide, 2‐isocyanobiphenyls smoothly underwent radical alkoxycarbonylation with carbazates to afford phenanthridine‐6‐carboxylates.
Solvent‐free protocols for Miyaura borylation and the one‐pot, two‐step homocoupling of aryl halides are reported for the first time. Bis(dibenzylideneacetone)palladium(0) [Pd(dba)2] is an optimal source of palladium for Miyaura borylation, while for one‐pot two‐step homocoupling palladium(II) acetate [Pd(OAc)2] gives highest yields. Aryl bromides are coupled most efficiently using the DPEphos ligand. Chlorides are coupled using XPhos. The developed protocols are robust, versatile and easily reproducible on a large scale.
The enantioselective allylation of thiophene‐2‐carbaldehyde with allyltrichlorosilane under Lewis base catalysis has been studied. The use of catalytic amount (1 mol%) of chiral bipyridine N,N′‐dioxides provided the corresponding 1‐(thiophen‐2‐yl)‐but‐3‐en‐1‐ol with asymmetric induction reaching 97% ee. The prepared chiral (S)‐1‐(thiophen‐2‐yl)‐but‐3‐en‐1‐ol was used as the crucial chiral building block in a formal total synthesis of duloxetine.
A transition metal‐free and efficient method for the synthesis of 3‐alkynylpyrrole‐2‐carboxylates from diynones and glycine esters or 2‐aminoacetophenone hydrochloride has been developed. This transformation provides a large range of substituted pyrroles in good to excellent yields with the elimination of water as the only by‐product. The detailed mechanistic studies elucidated that this transformation involves a Michael addition/intramolecular cyclodehydration process.
The first organocatalytic enantioselective approach to precursors of tubuvaline (pre‐Tuv) is presented employing a prolinamide‐catalyzed aldol reaction of easily accessible thiazole‐carbaldehyde with methyl isopropyl ketone “on water” in excellent yield as well as regio‐ and enantioselectivities. The analogues of pre‐Tuv were achieved using an L ‐proline‐catalyzed direct asymmetric aldol reaction of substituted thiazole‐carbaldehydes with acetone. A direct and flexible approach to the tubavaline (Tuv) core of tubusylins has been established employing the reductive amination of the pre‐Tuv species. The key aldol reaction should greatly expand the potential of this strategy to the synthesis of natural product tubulysins and a range of analogues.
We describe here a convenient and mild, carbon monoxide gas‐free palladium‐catalyzed procedure to obtain N‐substituted phthalimides with molybdenum hexacarbonyl as carbon monoxide precursor. These conditions tolerate a number of functional groups on the benzene ring as well as a number of amines and give the corresponding phthalimides in good to excellent yields.
A new copper‐mediated synthesis of α‐sulfonylethanone oximes from styrenes, sodium arylsulfinates and tert‐butyl nitrite (t‐BuONO; TBN) is presented. This intermolecular three‐component method enables the one‐step formation of C N and C S bonds under mild conditions, and represents a new, straightforward approach to α‐sulfonylethanone oximes.
A zinc diiodide (ZnI2)‐mediated direct synthesis of 2,3‐dihydroisoxazoles via a [3+2] cycloaddition reaction of the nitrones and non‐electron‐deficient terminal alkynes has been developed. This method was applied in the formal synthesis of HPA‐12 and aminoglucose.
An efficient synthetic procedure for dicyano‐cyclopropanation of alkenes using catalytic amounts of molecular iodine as a precatalyst and tert‐butyl hydroperoxide (TBHP) as a terminal oxidant under mild conditions has been developed. This catalytic reaction works especially well for the aryl‐substituted double bond affording products of cyclopropanation in high yields. A catalytic cycle based on the generated in situ hypoiodite species has been proposed.
A novel and efficient domino process has been developed for the synthesis of 1,4‐benzoxazepine derivatives from a range of readily accessible N‐tosylaziridines, 2‐iodophenols and isocyanides. This process involves the aziridine ring‐opening reaction with 2‐iodophenol, followed by a palladium‐catalyzed isocyanide‐insertion reaction. This regioselective and high‐yielding transformation could be extended to its application for the synthesis of natural products and biologically interesting heterocycles.
Iridium(III) and rhodium(III) complexes can catalyze the carbocyclization between 2‐phenylimidazo[1,2‐a]pyridine and α‐diazo esters. The reaction occurs via C H activation and dialkylation of the arene followed by intramolecular nucleophilic substitution. Iridium(III) and rhodium(III) catalysis offer complementary scopes with respect to the α‐diazo esters.
Cyclometallated NHC palladium complexes prepared from palladium(II) acetate [Pd(OAc)2] and unsymmetrical 1,3‐diarylimidazolinium salts catalyzed the hydroxymethylation of (hetero)arylboronic acids using an excess amount of formalin to afford (hetero)arylmethanols in good to satisfactory yields.
