Reduction of a ketone by lithium diisopropyl amide evidence for an electron-transfer mechanism

✍ Scribed by Lawrence T. Scott; Kevin J. Carlin; Thomas H. Schultz

• Publisher: Elsevier Science
• Year: 1978
• Tongue: French
• Weight: 100 KB
• Volume: 19
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)85691-4

✦ Synopsis

The widespread use of lithium diisopropyl amide (LDA) as a strong base has revolutionized numerous facets of mechanistic and synthetic organic chemistry in recent years;' however, it is less widely appreciated that amide bases can function also as reducing agents.' LDA, for example, reduces benzophenone (1) to benzhydrol (2) even at -78°C in tetrahydrofuran (eq 1). Certain enolizable aliphatic ketones (e.g., phenacyl bromide)3 even suffer reduction in competition with deprotonation by LDA. Ph Ph :c=o Li N(i-Pr)2 & \ /OH -78", THF * (1) Ph PhNC,H 1 2 ^ We have found that LDA in 20% HMPA/THF (6O"C, 24 hr) reduces benzophenone (1) not only to benzhydrol (2) but also to other products of higher molecular weight, including tetraphenylethylene o"xide (3). Benzpinacol (4) could not be found among the reduction products but was independently shown also to give-tetraphenylethylene oxide (3), benzhydrol (2) and benzophenone (1) under identical conditions.