the Beckmann fragmentation of alpha-alkoxy and alpha-alkoxy-alpha-alkyl oxime acetates have been successfully trapped as phosphonium salts, which were subsequently reacted with a variety of Grignard reagents to give the corresponding substituted products in good yields. Notably, this reaction proceeded smoothly even from alpha-alkoxy-alpha-alkyl oxime acetates.
Divergent Regioselectivity in the Base-Promoted Reactions of Cyclic Eight-Membered α-Ketols with Activated Halides
作者:Leo A. Paquette、Ivan Vilotijevic、David Hilmey、Jiong Yang
DOI:10.1021/ol027315z
日期:2003.2.1
[reaction: see text] Deprotonation of 2-hydroxycyclooctanone followed by exposure to an allylic or benzylic halide proceeds very selectively to give the product of C-alkylation. The effect of Delta(5,6)-unsaturation is to promote instead the formation of the O-alkylated derivative. This crossover in kinetic preference is attributed to an inability of the olefinic system to attain a conformation conducive
Base-Promoted Ring Contractionof Eight-Membered Cyclic Acyloins and their Ethers to<i>C</i>
<sub>s</sub>-Symmetric α-Ketols
作者:Leo A. Paquette、Ivan Vilotijevic、Jiong Yang、David Hilmey
DOI:10.1055/s-2003-41003
日期:——
In the presence of potassium hexamethyldisilazide and 18-crown-6in THF at room temperature, 2-benzyloxycyclooctanone andits Î5-unsaturated congener undergo a two-stagerearrangement to give symmetrical seven-membered ringproducts. The pathway consists of the sequential operation of anO → C 1,2-shift and an α-ketol rearrangement.The greater thermodynamic stability of the cycloheptane or cycloheptenegenerated in this fashion is substantiated by MM3 calculations.