Reactions of Aryl Grignard Reagents with 2,2,4-Trimethyl-3-hydroxy-3-pentenoic Acid β-Lactone¹

Synthesis of 1,3-diketones through ring-opening of ketoketene dimer β-lactones

“…3 We initially investigated the reaction of methylphenylketene dimer 1b with excess n-BuLi (2 equiv) in THF at À78°C and were surprised to find that 1,3-diketone 6b (88%, dr = 86:14), derived from single addition, was obtained as the major product rather than retro-aldol product 5b (Scheme 3). 4,5 Interestingly, relatively few studies have investigated diastereoselectivity in 1,3-diketone formation. 23 Although quenching the reaction with excess water after warming from -78°C to room temperature led to good diastereoselectivity (dr = 86: 14), we subsequently found that slightly higher diastereoselectivity could be obtained when the reaction was quenched with water (93%, dr = 89:11) or acetic acid (72%, dr = 90:10) at À78°C.…”