Rhodium-Catalyzed Enantioselective [4+2] Cycloadditions of Vinylcarbenes with Dienes

The reaction of 2-siloxycyclo-1,3-dienes with E-vinyldiazoacetates in the presence of the bulky chiral dirhodium tetracarboxylate catalyst, Rh₂ (R-p-PhTPCP)₄ results in an enantioselective [4+2] cycloaddition, in which three new stereogenic centers are formed. The [4+2] cycloadducts are generated as single diastereomers with high enantiocontrol (95-98 % ee). When the diene contains an additional stereogenic center, effective kinetic resolution can be achieved.

Mechanism and enantioselectivity of the asymmetric [3+2]-annulation between N-methylindole and enoldiazoacetamide catalyzed by prolinate-coordinated dirhodium: A theoretical study

The mechanistic study of Rh₂(S-MSP)₄-catalyzed asymmetric [3 + 2]-annulation of N-methylindole and enoldiazoacetamide carbenoid to produce C2,C3-fused indole skeleton has been carried out by combining the density functional theory and semi-empirical method with ONIOM methodology. The mechanism and origin of enantioselectivity were disclosed by our calculations. The cycloaddition process was initiated by vinylogous attack of indole on the enol terminus of carbenoid, which was considered to be the enantio-controlling step. Followed by ring closure step where C-Rh bond adds to the iminium, adduct was afforded enantioselectively. The rate-controlling step, depending on the pathways the reaction proceeds along, could be either one of the two steps. Moreover, we elucidated the effect of weak interaction on the enantioselectivity using the independent gradient model analysis and provided possible insight into reaction design. The catalytic cycle was also kinetically interpreted in a non-conventional way, which is the energetic span model, realized by the AUTOF program.

Stereoselective Synthesis of Isoxazolidines via Copper-Catalyzed Alkene Diamination

A convenient copper-catalyzed intramolecular/intermolecular alkene diamination reaction to synthesize 3-aminomethyl-functionalized isoxazolidines under mild reaction conditions and with generally high levels of diastereoselectivity was achieved. This reaction demonstrates that previously underutilized unsaturated carbamates are good [Cu]-catalyzed diamination substrates. Sulfonamides, anilines, benzamide, morpholine, and piperidine can serve as the external amine source. This relatively broad amine range is attributed to the mild reaction conditions. Reduction of the N-O bond could also be achieved, revealing the corresponding 3,4-diamino-1-alcohols efficiently.