Asymmetric and Nonasymmetric Addition of RLi and RMgX to 3-Methoxynaphthalen-2-yl Oxazolines and Imines. An Approach to Substituted 2-Tetralones

Chiral and achiral 3-methoxynaphthalen-2-yl oxazolines 4a,b failed to undergo an aromatic nucleophilic displacement of the 3-methoxy group with organolithium reagents and instead afforded dihydronaphthalenes 9 and 14 in 30−95% yield. Dihydronaphthalenes 9 (racemic) and 14 (nonracemic) were easily converted into the corresponding aldehydes 15. Alternatively, aldehydes 15 were prepared via tandem addition of Grignard reagents to imines 17 in 50−65% yield. Aldehydes 15 served as precursors to 3,3,4-trisubstituted 2-tetralones 16. Use of methyl chloroformate to trap the azaenolate derived from 17f and i-PrMgCl afforded, in 65% yield, a versatile synthetic intermediate 23 which may serve to access 4-alkyl-, 3,4-dialkyl-, 3,4-disubstituted and 3,3,4-trisubstituted 2-tetralones with diverse substitution patterns.