Enantioselective synthesis of rigid 2-aminotetralins. Utility of silicon as an oxygen and nitrogen surrogate in the tandem addition reaction

Dimethylphenylsilyllithium undergoes a highly diastereoselective conjugate addition to chiral naphthyloxazoline 11. Electrophilic trapping of the resu lting aza-enolate affords the tandem addition product (12) in high yields a s a single diastereomer. The silicon, thus incorporated, may be protodesily lated and undergoes a Tamao oxidation to afford the corresponding alcohol. By chemical modification of the oxazoline, both the gamma-lactone (28) and the delta-lactone (37) were prepared. Reduction of each lactone followed by oxidation of the ensuing diol gave the keto aldehyde. Double reductive ami nation of the 1,4-dicarbonyl (from the gamma-lactone) allowed the synthesis of two novel hexahydrobenz[e]indoles, 20 and 35. Double reductive aminatio n of the 1,5-dicarbonyl (from the delta-lactone) gave access to two novel o ctahydrobenzo[f]quinolines, 41 and 43. An unprecedented rearrangement of ni tro alcohol 26 into lactone 28 is described and a reasonable mechanism for its formation postulated.