87190-31-6Relevant articles and documents
Directed chiral synthesis by way of α-chloro boronic esters
Matteson, Donald S.,Ray, Rahul,Rocks, Richard R.,Tsai, David J.
, p. 1536 - 1540 (2008/10/08)
Homologation of (+)-pinanediol boronic esters, RBO2C10H16, with (dichloromethyl)lithium has yielded αS α-chloro boronic esters, RCHClBO2C10H16, in diastereomeric purities from 74% (R = CH3) to 98% (R = C6H5), with typical alkyl groups (n-butyl, cyclohexyl) ranging from 83 to 90%. Grignard or lithium reagents replace the α-chloro function by alkyl with inversion. Peroxidic oxidation of the residing boronic esters proceeds with retention of configuration to yield alcohols of known rotation and absolute configuration. Purification of (+)-pinanediol to 100% enantiomeric excess (ee) was accomplished by way of recrystallization of sodium bis(pinanediol) borate, which on acidification yields a 1:1 mixture of pinanediol and pinanediol boric acid ester, not freed from boron but used directly to make pinanediol boronic esters of 100% ee. The synthetic utility of these processes was demonstrated by highly stereoselective and efficient synthesis of (2S,3S-3-phenyl-2-butanol and (2R,3S)-3-phenyl-2-butanol. The latter synthesis involved construction of the first chiral center from (+)-pinanediol phenylboronate, cleavage of the (+)-pinanediol with boron trichloride and replacement by (-)-pinanediol, and then introduction of the second chiral center.
