Diastereoselective Formation of Cyanohydrins from α-Alkoxy Aldehydes
摘要:
[GRAPHICS]The reaction of alpha-alkoxy aldehydes with Et(4)NAG(CN)(2) or Me3SiCN in the presence of MgBr2. OEt2 in CH2Cl2 at 0 degrees C gives the corresponding syn cyanohydrins in good yield with high diastereoselectivity. Excess MgBr2. OEt2 (typically 5 equiv) is required for high diastereoselectivity. Et4NAg(CN)(2) (but not Me3SiCN) is sufficiently reactive to give cyanohydrins at -78 degrees C, and higher diastereoselectivity is obtained at this temperature.