Electronic control of stereoselectivity in the metal hydride reductions of 7-benzonorbornenones

✍ Scribed by Keiji Okada; Seiji Tomita; Masaji Oda

• Publisher: Elsevier Science
• Year: 1986
• Tongue: French
• Weight: 228 KB
• Volume: 27
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)84607-9

✦ Synopsis

Electronic control of the anti/syn stereoselectivity in metal hydride reductions of 7-benzonorbornenones &-d-is proposed. Stereoselectivity in nucleophilic additions toward 7-norbornenone has received considerable attention. Experimental data so far available confirm that the nucleophiles stereoselectively attack the carbonyl group from the syn-side of the double bond. For example, the reactions with sodium borohydride,' Grignard reagents, 2a,b alkyl lithium reagents,3 diazomethane,4 and with sulfonium5 or sulfoxonium 2b ylides gave the products of syn attack in a stereoselective or stereospecific manner. Exceptions can be seen in the reaction with Jinyl lithium6 and phenyl lithium.' Mechanistic problems as to whether the observed stereoselectivity is due to steric or electronic effects are controversial. Attack from the anti side of the double bond seems to be slightly more hindered owing to the steric repulsion of the H5 6exo protons with incoming nucleophiles.