No abstract

Unprecedented phosphine-catalyzed [4+ +1] cycloadditions of allenyl imides have been discovered using various N-based substrates including methyl ketimines,e namines,a nd ap rimary amine.T hese transformations provideaone-pot access to cyclopentenoyl enamines and imines,o r( chiral) glactams through two geminal C À Cb ond or two C À Nb ond formations,r espectively.S everal P-based key intermediates including a1 ,4-(bis)electrophilic a,b-unsaturated ketenyl phosphonium species have been detected by 31 PNMR and HRMS analyses,w hich shed light on the postulated catalytic cycle.T he synthetic utility of this new chemistry has been demonstrated through ag ram-scaling up of the catalytic reaction as well as regioselective hydrogenation and double condensation to form cyclopentanoyl enamines and fused pyrazole building blocks,respectively. Scheme 1. Pioneering examples of allene-imine annulations through nucleophilic catalysis.

A CuII‐catalyzed asymmetric 1,3‐dipolar cycloaddition using β‐fluoroalkyl alkenyl arylsulfones as dipolarophiles and glycine/alanine iminoesters as azomethine ylide precursors has been developed. Remarkably, a catalyst loading as low as 0.5 mol % is highly efficient. Accordingly, a wide range of enantioenriched 3‐fluoroalkyl pyrrolidines, as well as Δ2‐pyrroline and pyrrole derivatives, are generated in good to excellent yields with high asymmetric induction. This synthetic approach is diastereodivergent in that exo‐adducts could be converted into the corresponding exo′‐adducts by 1,8‐diazabicyclo[5.4.0]undec‐7‐ene mediated epimerization at C2 of the pyrrolidine core. The free‐energy profiles from DFT calculations suggest the Michael addition of the 1,3‐dipole to be the rate‐ and enantiodetermining step, and the origin of stereoselectivity is studied by means of the noncovalent interaction (NCI) analysis.

An organocatalyzed aqueous media domino reaction is developed for the regioselective synthesis of benzo[4,5]imidazo[1,2-a]pyrimidines and pyrido[2,3-d]pyrimidin-2-amines.