R,R)-Butanediol (dichloromethy1)boronate (1) with I equiv. allylmagnesium halide yields (R,R)-2,3butanediol (1 S)-(1 -chloro-3-butenyl)boronate (3) together with the diallylated product (R,R)-2,3-butanediol(1 -allyl-3-butenyl)boronate (4). The formation of 4 is unprecedented in reactions of a-chloroboronic esters with Grignard reagents. With methylmagnesium bromide 3 yielded (R,R)-2,3-butanediol
( I S)-(I -methyl-3-butenyl)boronate (3, which failed to
hydrolyze with water. Hydrolysis of 3 yielded impure a-chloroboronic acid, which was esterified with pinacol and treated with methvlmagnesium bromide to form 6, which with (dichloromethy1)Iithium followed by methylmagnesium bromide yielded diastereomeric boronic esters 7 and 8. Oxidation by hydrogen peroxide yielded (2S,3S)-and (2R,3S)-3methyl-5-hexen-2-01 (9 and 10, ees unknown). Treatment o f (s)-pinanediol allylboronate (1 1) with (dich1oromethyl)lithium at -100°C followed by zinc chloride at up to 25°C has proceeded in the normal way to form (s)-pinanediol ( I S)-(l-chloro-3-butenyl)boronate (12), which has been elaborated via 13, 14, and 15 to (2S,3S)-3-methyI-5-hexen-2-01 (9) in 95% de.