5a,6,7,8,9,ll-Hexahydropyrido

Electrophilic heterocyclizations of 2-(pent-l-en-5-yl)-l,3-benzoxazin-4-ones (142) and their C-2 epimers afforded diastereomeric mixtures of 9-methyl-5a,6,7,8,9,ll-hexahydropyrido[2,l-h][l,3]benzoxazin-10-ones (143 and 144), and their C-5a epimers, respectively, containing the 9-methyl group in the pseudo-axial orientation (89TL7321 90TL6765). Diastere-omers 143 and 144 interconvert in response to acidic catalysis (89TL7321). 

Reaction of 5a,6,7,8,9,ll-hexahydropyrido[2,l- >][l,3]benzothiazine-7,l 1-dione (47, X = S, R = H) and 2-amino-6-fluorobenzamidine dihydrochloride in boiling EtOH yielded a diastereomeric mixture of spiro derivatives 48 (X = S, R = H), which were separated by flash column chromatography (OOMIPl). 

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