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.

The intermolecular [2 + 2] cycloaddition/isomerization between allenyl imides and N-(2-methoxyphenyl) aldimine counterparts catalyzed by a Ni­(ClO4)2·6H2O Lewis acid at room temperature was discovered, providing a facile access to 1-azadiene derivatives with high atom economy. The incorporation of an 2-oxazolidinone group into allene amides resulted in unusual reactivity for the imine-metathesis and synthetic application to a chiral γ,δ-unsaturated β-ketoimide. A mechanistic experiment using density functional theory (DFT) computation in CH2Cl2 with the B3LYP functional rationalized the proposed catalytic pathway involving initial stepwise [2 + 2] cycloaddition to provide an azetidine species, two-time proton transfer to form a 2-azetine intermediate, and final conrotatory ring opening for trans-1-azadiene-based substances.

A three-component Petasis-type gem-difluoroallylation reaction of using pinacol gem-difluoroallylboronates, aldehydes or isatin, and β-amino alcohols enabled by the neighboring hydroxyl group in amine is reported, affording various racemic and chiral gem-difluorohomoallylamine derivatives with good to excellent results. Based on the control experiment and stereochemistry of the product, a proposed reaction pathway is illustrated to clarify the origin of regio- and stereoselectivity under protic solvent conditions.

CsOH·H2O-catalyzed formal [3 + 3] cycloadditions of allenyl imide with β-ketoesters, 1,3-diketones or β-ketonitriles for the synthesis of tetrasubstituted 2-pyrone derivatives were reported.

Unprecedented phosphine-catalyzed [4+1] cycloadditions of allenyl imides have been discovered using various N-based substrates including methyl ketimines, enamines, and a primary amine. These transformations provide a one-pot access to cyclopentenoyl enamines and imines, or (chiral) γ-lactams via two geminal CC bond or two C-N bond formations, respectively. Several P-based key intermediates including a 1,4-(bis)electrophilic α,βunsaturated ketenyl phosphonium species have been detected by 31 P NMR and HRMS analyses, which shed light on the postulated catalytic cycle. The synthetic utility of this new chemistry has been demonstrated through a gram-scaling up of the catalytic reaction as well as regioselective hydrogenation and double condensation to form cyclopentanoyl enamines and fused pyrazole building blocks, respectively.