Pd-Catalyzed Cycloaddition of Vinylcyclopentenes with Trimethylenemethane. Substituent Effect on [4+3]<i>vs</i>[3+2] Selectivity
作者:Barry M. Trost、Shoko Yamazaki
DOI:10.1246/cl.1994.2245
日期:1994.12
The Pd-catalyzed reaction of 2-vinylcyclopentenes 2 and 3 with trimethylenemethane gave [4+3] and [3+2] cycloadducts. Derivatization of 2-vinylcyclopentenones with bulky ketal substituents served to enhance seven-membered ring formation.
Asymmetric synthesis of allylic sulfones useful as asymmetric building blocks.
作者:Barry M. Trost、Michael G. Organ、George A. O'Doherty
DOI:10.1021/ja00143a007
日期:1995.9
Construction of sulfones in enantiomerically pure form provides a great opportunity to enhance their value as synthetic building blocks. Allylic sulfones, in particular, have great flexibility derived from sulfone-controlled additions to the double bond. Two strategies have been developed based upon the ability to effect asymmetric allylic alkylations with palladium employing ligands derived from c(2) symmetric diamines and 2-(diphenylphosphino)benzoic acid. Desymmetrization of meso-2-ene-1,4-diol diesters does not involve the nucleophile in the enantiodiscriminating step and thus should, a priori, not depend upon the nature of the nucleophile. Indeed, such desymmetrization of such a diester in the presence of a sulfinate anion gave excellent enantioselectivity. On the other hand, conversion of both enantiomeric allylic esters to enantiomerically pure allylic sulfones requires sodium benzenesulfinate to participate in the enantiodiscriminating step. Five-, six-, and seven-membered substrates all gave excellent enantioselectivities. A catalytic phase transfer system proved most efficacious on larger scales. propagating the asymmetry requires diastereoselective functionalization of the double bond. While epoxidation proved excellent for the five-membered ring case and satisfactory for the six-membered ring case, it was unsatisfactory in the seven-membered ring case. Osmium tetroxide-catalyzed cis-dihydroxylation gave excellent diastereoselectivities in the six- and seven-membered ring cases. Reductive cleavages produced enantiomerically pure allylic alcohols. Base-catalyzed elimination generated enantiomerically pure gamma-hydroxy-alpha,beta-unsaturated sulfones from which further stereogenic centers were produced by diastereoselective conjugate additions. Notably, an asymmetric cyclopentenone annulation using palladium-catalyzed cycloadditions now derives from racemic allyl alcohols.
In(+3) as a chemoselectivity switch for TMM-PDL2 cycloadditions to ynones
作者:Barry M. Trost、Sunaina Sharma、Thomas Schmidt
DOI:10.1016/s0040-4039(00)79282-3
日期:1993.11
The previous inability to effect palladium catalyzed cycloadditions of 2-trimethylsilylmethallyl acetate to the carbonyl group of ynones is rectified by the employment of indium acetylacetonoate as a cocatalyst.
Coordinative cocatalysis via indium(3+). A chemoselectivity switch for palladium-catalyzed cycloadditions