Rhodium-Catalyzed Enantioselective Isomerization of meso-Oxabenzonorbornadienes to 1,2-Naphthalene Oxides.

Herein we describe a rhodium-catalyzed enantioselective isomerization of meso-oxabicyclic alkenes to 1,2-naphthalene oxides. These potentially useful building blocks can be accessed in moderate to excellent yields with impressive enantioselectivities. Additionally, experimental findings supported by preliminary computations suggest that ring-opening reactions of bridgehead disubstituted oxabicyclic alkenes proceed through the intermediacy of these epoxides and may point to a kinetically and thermodynamically favored reductive elimination as the origin for the observed enantioselectivities.

Rhodium-Catalyzed Asymmetric Cycloisomerization and Parallel Kinetic Resolution of Racemic Oxabicycles.

While desymmetrizations by intermolecular asymmetric ring-opening reactions of oxabicyclic alkenes with various nucleophiles have been reported over the past two decades, the demonstration of an intramolecular variant is unknown. Reported herein is the first rhodium-catalyzed asymmetric cycloisomerization of meso-oxabicyclic alkenes tethered to bridgehead nucleophiles, thus providing access to tricyclic scaffolds through a myriad of enantioselective C-O, C-N, and C-C bond formations. Moreover, we also demonstrate a unique parallel kinetic resolution, whereby racemic oxabicycles bearing two different bridgehead nucleophiles can be resolved enantioselectively.

Modular synthesis of naphthothiophenes by Pd-catalyzed tandem direct arylation/Suzuki coupling.

A short and highly modular three-step synthesis of a new class of substituted naphthothiophenes has been developed exploiting a Pd-catalyzed tandem direct arylation/Suzuki coupling transformation as the key step.

Asymmetric one-pot sequential organo- and gold catalysis for the enantioselective synthesis of dihydropyrrole derivatives.

A direct asymmetric one-pot synthesis of optically active 2,3-dihydropyrroles from propargylated malononitrile and N-Boc-protected (Boc = tert-butoxycarbonyl) imines is presented. The approach is based on a bifunctional organocatalytic Mannich-type reaction and a subsequent gold-catalyzed alkyne hydroamination and isomerization. The compatibility of both catalytic systems is presented and the overall transformation results in good yields (up to 70 %) with high selectivities (endo/exo > 10:1) and enantioselectivities (up to 88 % ee). The absolute configuration of the final products is unambiguously established by X-ray analysis. To highlight the synthetic potential of the accessed heterocyclic compounds, their transformation into 1-pyrrolines, which represent direct precursors of pyrrolidines, is presented.

Organocatalytic enantioselective one-pot synthesis and application of substituted 1,4-dihydropyridines--Hhantzsch ester analogues.

An easy and simple one-pot approach for the formation of optically active substituted 1,4-dihydropyridines by using asymmetric organocatalysis is presented. The one-pot reaction of alpha,beta-unsaturated aldehydes with beta-diketones or beta-ketoesters and primary amines gives optically active 2,3-substituted 1,4-dihydropyridines in moderate yields and with enantioselectivities up to 95 % ee. It is also demonstrated that the optically active 1,4-dihydropyridines can be used in situ for the direct enantioselective reduction of, for example, alpha-ketoesters with high enantioselectivity.