Reactions of 6-[bis(trimethylsilyl)amino]-5,6-dihydro-4H-1,2-oxazines

1,2-Oxazine 1 was converted into an unusual condensation product 5 by treatment with tetra-n-butylammonium fluoride. The hydrogenolysis of 1 with Pd/C as catalyst provided the expected primary amine 9, whereas the same reaction with the ethoxycarbonyl-substituted 1,2-oxazine 2 as starting material gave the 4-methylproline derivative 10 after N-protection. Deprotonation at C-4 of 1 required rather harsh conditions but cleanly afforded the corresponding lithiated intermediate 11. Treatment of 11 with electrophiles provided the C-4-substituted derivatives 12–16 in good to moderate yield, but generally with very high diastereoselectivity. The overall substitution process preferentially occurs with retention of configuration which is explained by assuming ion pair structure B for intermediate 11.