(2aS,3S,6S,7S,7bR)-7-[(dimethylphenyl)-silyl]-2-oxo-6-[(1R,2S)-2- phenylcyclo-hexyloxy]-2a,3,6,7,7a,7b-hexahydro-2H-1,4,5-trioxa-4a- azacyclopenta[cd]indene-3-carboxylic acid 1-methylethyl ester.

The structure of the title compound, C31H39NO7Si, was determined and found to be a fused tricyclic nitroso acetal. Remarkable features include a twist-boat conformation of the tetrahydro-1,2-oxazine ring and a highly pyramidalized N atom [Sigma (angles) = 310.6(6) degrees]. Three of the contiguous stereocenters in the nitroso acetal are of the same correct relative and absolute configuration as is found in (+)-crotanecine.