Enantioselective[3 t 2]cycloadditions of terminal allenoates withβ-sulfonyl-α,β-unsaturated ketones

A highly efficient and mild method for[3 t 2]cycloaddition ofβ-sulfonyl-α,β-unsaturated ketones with terminal allenoates was well-explored and developed.The reactions were successfully performed by applying multifunctional chiral phosphine P6 which was screened from eight chiral phosphorus reagents to finally result in a variety of enantioenriched sulfone-substituted cyclopentenes with two chiral centers(up to 81%yield with 94%ee).Moreover,2.5 mol%catalytic equivalents were proved to be feasible when this reaction was performed on a 10 mmol scale.

Recent advances in tertiary amine Lewis base-promoted cycloadditions of allenoates

Lewis base-catalyzed annulations of allenoates have been one of the most powerful synthetic strategies for the synthesis of various valuable cycles,especially in the preparation of biologically active natural products and pharmaceuticals.Generally,the effective Lewis bases mainly include tertiary phosphine,NHC and tertiary amine catalysts,among those catalysis,tertiary amine Lewis bases have proven to be effective catalysts for a range of synthetic transformations.In the past decades,tremendous progress in-volving tertiary amines-promoted cycloaddition of allenoates has been made in the chemoselective con-struction of valuable motifs.This review describes a comprehensive and updated summary of tertiary amine Lewis base-promoted annulation reactions of allenoates.Diverse reactivities,chemoselectivties and detailed reaction mechanisms will be highlighted in this review.

Enantioselective synthesis of mixed 3,3’-bisindoles via a phosphine-catalyzed umpolung γ-addition of 3’-indolyl-3-oxindoles to allenoates

An enantioselective umpolung γ-addition reaction of 3’-indolyl-3-oxindoles to allenoates catalyzed by amino acid-derived bifunctional phosphine catalysts has been developed. A wide range of chiral mixed 3,3’-bisindole scaffolds containing an all-carbon quaternary stereogenic center were obtained in high yields and with excellent enantioselectivities. 3,3’-Bisindoles are valuable synthetic intermediates, the employment of which led to formal total syntheses of(+)-Chimonanthine,(+)-Folicanthine and(-)-Calycanthine, as well as facile creation of useful pyrrolidinoindoline core structure.

Double[3+2] cycloaddition of nitrile oxides with allenoates:Synthesis of spirobidihydroisoxazoles

The double [3 + 2] cycloaddition of allenoates with nitrile oxides is presented. The reaction worked well under mild reaction conditions to give the spirobidihydroisoxazole in moderate to excellent yields with excellent diastereoselectivities. The two dihydroisoxazole rings have been formed via a sequential double [3 + 2] cycloaddition.

Facile Synthesis of Spirooxindole-Cyclohexenes via Phosphine-Catalyzed [4-1-2] Annulation of α-Substituted Allenoates

A phosphine-catalyzed [4＋2] annulation of a-substituted allenoate with exocyclic alkene moiety of oxindoles or indan-1,3-diones has been developed. Thus, under the catalysis of PPh3 （20 mol%）, a series of spirooxindole- or spiroindan-1,3-dione-cyclohexenes have been obtained in moderate to excellent yields and regioselectivity from the annulations of a-methyl allenoates with 3-methyleneoxindoles or 2-methyleneindan-1,3-diones. This method offers an easy access to structurally novel spirocyclohexenes.

N-Heterocyclic Carbene-Catalyzed [2＋2＋2] Annulation of Allenoates with Trifluoromethylketones

In contrast with the reported phosphine- and DABCO-catalyzed [3 ＋ 2] and [2 ＋2] annulation of allenoates with trifluoromethylketone, the [2＋2＋2] annulation of allenoates and two molecules of trifluoromethylketone was found under the condition of N-heterocyclic carbene catalysis.

Assembly of 3-sulfonated 2H-pyrrol-2-ones through the insertion of sulfur dioxide with allenoic amides

Generation of 3-sulfonated 2 H-pyrrol-2-ones through a three-component reaction of allenoic amides,sulfur dioxide,and aryldiazonium tetrafluoroborates under metal-free conditions is achieved.This transformation proceeds under mild conditions without the addition of catalysts or additives,giving rise to 3-sulfonated 2 H-pyrrol-2-ones in moderate to good yields.Good functional group compatibility is observed.A plausible mechanism is proposed,which is initiated by aryl radicals formed in situ from aryldiazonium tetrafluoroborates and DABCO·(SO2)2.Additionally,excellent chemoselectivity and regioselectivity are presented in this transformation.