RESUMEN
A highly diastereoselective and enantioselective Cu(II)/SaBOX-catalyzed [2 + 2] cycloaddition of methylidenemalonate and multisubstituted alkenes was developed to furnish optically active cyclobutanes in high yields with >99/1 dr and up to >99% ee. By application of the newly developed method, the total synthesis of (+)-piperarborenine B was completed in eight steps from methylidenemalonate and olefin in 17% overall yield with >99/1 dr and 99% ee.
RESUMEN
An efficient [4 + 3] cycloaddition reaction of D-A cyclopropanes with dienes has been successfully developed. The reaction proceeds well with various dienolsilyl ethers in the presence of Lewis acid, delivering a variety of cycloheptenes and [n,5,0]carbobicycles with excellent stereoselectivity. The asymmetric version of this reaction is also realized using a newly designed chiral Cy-TOX ligand, providing a new approach to access optically active cycloheptenes and [n,5,0]carbobicycles. Mechanisic study reveals that the reaction involves a stepwise pathway, which undergoes an unusual ring opening of five-membered [3 + 2] intermediate and sequential intramolecular cyclization to afford the thermodynamically stable [4 + 3] annulation product.
Asunto(s)
Alquenos/química , Compuestos Bicíclicos con Puentes/síntesis química , Cicloheptanos/síntesis química , Ciclopropanos/química , Compuestos Bicíclicos con Puentes/química , Reacción de Cicloadición , Cicloheptanos/química , Ácidos de Lewis/química , EstereoisomerismoRESUMEN
The first highly diastereoselective and enantioselective catalytic formal [4 + 3] cycloaddition of 1,1-cyclobutane diester with nitrone has been developed. Sterically hindered chiral SaBOX/Cu(II) complex promotes the reaction efficiently with a broad substrate scope, producing a range of multifunctionalized optically active 1,2-oxazepanes with excellent stereocontrol (up to >99/1 dr and 97% ee).