Aminocyclopentitols from N-alkylpyridinium salts:: A photochemical approach

The photolysis of N-alkylpyridinium halides 9a-e in alkaline H2O gave 6-azabicyclo[3.1.0]hexenol derivatives 10a-e. N-Substituents bearing ether, acetal, and alcohol functions were found to do nor adversely influence the photochemical reaction course. The free OH groups of the N-(3-hydroxypropyl) derivative 10 d were protected by benzoylation. The ensuing dibenzoate 14 underwent stereocontrolled opening of the aziridine ring on reaction with MeSH/BF3 to give a thioether 15. With benzoic acid in CHCl3, 10 d gave the 4-hydroxy-5-aminocyclopent-2-enyl benzoate 11. The meso-2-aminocyclopent-4-ene-1,3-diol 12 was obtained by hydrolysis of 11. On reaction with Boc(2)O and NaI, the aziridine ring of 14 was converted to a bicyclic compound 17. Hydrolysis of 17 provided the trans-1,3-diol 18, the epimer of 12. Face-selective dihydroxylation of Boc-protected 12 gave a meso-aminocyclopentanetetrol 23 which was characterized upon peracetylation. Dihydroxylation of 15 provided a racemic analogue of epi-mannostatin A (26).