rel-(1R,6S,7S,8R,9S)-9-methyl-8-phenyl-6-[(1s,2R)-(2-phenylcyclohexyl) oxy]-4-aza-3,5-dioxatricyclo[5.2.1.0(4,9)]decane.

The structure of the title compound, C26H31NO3, was determined by X-ray crystallography. It was found to be a unique bridged tricyclic nitroso acetal. Notable features include a chair conformation of the tetrahydro-1,2-oxazine ring and a highly pyramidalized N atom [sigma angles = 314.

(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].