Chiral Synthesis via Organoboranes. 21. Allyl- and Crotylboration of α-Chiral Aldehydes with Diisopinocampheylboron as the Chiral Auxiliary

Article abstract of DOI:10.1021/jo00268a017

B-Allyldiisopinocampheylboranes <18, prepared from (+)-α-pinene; 19, prepared from (-)α-pinene> have been screened for diastereofacial selectivity in their reaction with α-substituted chiral aldehydes.Both syn and anti products have been obtained in very high diastereoselectivities.Further, (E)-crotyldiisopinocampheylboranes <20, prepared from (+)-α-pinene; 21, prepared from (-)-α-pinene> and (Z)-crotyldiisopinocampheylboranes <22, prepared from (+)-α-pinene; 23, prepared from (-)-α-pinene> have been used for diastereofacial selectivity in their reaction with α-substituted chiral aldehydes.These crotylboranes, 20-23, are highly diastereoselective reagents and the corresponding (3,4- and 4,5-)-anti,syn, -anti,anti, and -syn,anti products have been obtained in very high facial selectivities; even the syn,syn product has been obtained in moderately good facial selectivity.Finally, the relative efficiences of the various chiral auxiliaries utilized in the literature for the allyl- and crotylboration have been compared with those achieved by the diisopinocampheylboron moiety.