Metalation and subsequent transformations of β-pinene

Abstract

β-Pinene, unlike α-pinene, is easily and quantitatively metalated with butyllithium/TMEDA. The resulting allyllithium•TMEDA is easily isolated, with the racemic material crystallizing preferentially, even from 92 % ee solutions. The complex is indefinitely stable in C6D6, and has been fully characterized. Reaction with formaldehyde favors alkylation at the less substituted allyl position with modest regioselectivity (2:1), and the corresponding Grignard reagent (made by transmetalation with MgBr2) reacts very regioselectively at the more substituted position with formaldehyde and diphenyl disulfide (99-92 %, resp.). The two phenyl sulfide isomers are observed to equilibrate when exposed to heat or UV light. This easy metalation provides access to a versatile chiral-pool-derived allyl nucleophile.