Gold catalyzed intermolecular addition of alcohols toward the proximal allenic double bond of 4-vinylidene-2-oxazolidinones gives hydroalkoxylation products, which can be easily converted into the corresponding novel spiro dihydrofuran or dihydropyran derivatives in high yield.
4-Ethenylidene-2-oxazolidinones 2, 6, and 9 are prepared in reasonable yields by the reaction of 2-butyn-1,4-diol biscarbamates in the presence of catalytic amounts of Pd-2(dba)(3) . CHCl3 (0.005 equiv) ad triethylamine (0.1 equiv). The allenic three carbons are not aligned straight, but considerably distorted (173.6 degrees); the enamine double bond is reactive toward unsaturated amides (providng 4) and methyl vinyl ketone (providing 10). (C) 1997 Elsevier Science Ltd.
Preparation, Structure, and Unique Thermal [2+2], [4+2], and [3+2] Cycloaddition Reactions of 4Vinylideneoxazolidin-2-one
good to excellent yields. Alkenes react with 2 with complete retention of configuration. The [2+2] cycloaddition is concluded to proceed via a concerted [(pi(2s)+pi(2s))(allene) + pi(2s)] Huckel transition state on the basis of experimental evidences and quantum mechanical methods. Some highly polarized enones and nitrile oxide, on the other hand, react with 2 selectively at the internal C(4)=C(alpha)
A Useful Allene for the Stereoselective Synthesis of Protected Quaternary 2-Amino-2-vinyl-1,3-diols
作者:Aleix Rodríguez、Xavier Ariza、Miguel A. Contreras、Jordi Garcia、Paul Lloyd-Williams、Nerea Mercadal、Carolina Sánchez
DOI:10.1021/acs.joc.6b02765
日期:2017.2.3
Treatment of readily available allene 1 with Cy2BH followed by addition of an aldehyde led to quaternary protected 2-amino-2-vinyl-1,3-diols in high yield and excellent stereochemical purity. The choice of benzoyl as N-protecting group is critical since the observed N- to O-Bz transfer during the process prevents later undesired isomerizations in the adducts and keeps all heteroatoms protected.