ORGANOBORANES. 32. HOMOLOGATION OF ALKYLOBORONIC ESTERS WITH METHOXY(PHENYLTHIO)METHYLLITHIUM: REGIO- AND STEREOCONTROLLED ALDEHYDE SYNTHESIS FROM OLEFINS VIA HYDROBORATION.

Article abstract of DOI:10.1021/ja00358a017

Homologation of 2-alkyl-1,3,2-dioxaborinanes, RBO//2C//3H//6 (1), to alpha -methoxyalkyl derivatives, RCH(OMe) BO//2C//3H//6 (2), was achieved by reaction with LiCH(OMe) SPh, followed by treatment with HgCl//2. The intermediates 2 were smoothly oxidized with hydrogen peroxide in a pH 8 phosphate buffer to give the corresponding aldehydes, RCHO (3). The alkyl groups of 1 were introduced by the hydroboration method. Thus, heptanal, 3-phenylbutanal, 2-ethylpentanal, cyclohexanecarbaldehyde, trans-2-methylcyclopentanecarbaldehyde, and exo-norbornanecarbaldehyde were prepared in fair to good yields from 1-hexene, 2-phenylpropene, 3-hexene, cyclohexene, 1-methylcyclopentene, and norbornene, respectively. Furthermore, both threo- and erythro-2,-dimethylpentanal were obtained in 96% diastereomeric purity from (E)- and (Z)-3-methyl-2-pentene, respectively. The migration of the alkyl group from boron to carbon proceeds with retention of configuration.