Aminocyclopentitols from N ‐Alkylpyridinium Salts: A photochemical approach

The photolysis of N ‐alkylpyridinium halides 9a – e in alkaline H 2 O gave 6‐azabicyclo[3.1.0]hexenol derivatives 10a – e . N –Substituents bearing ether, acetal, and alcohol functions were found to do not adversely influence the photochemical reaction course. The free OH groups of the N –(3‐hydroxypropyl) derivative 10d were protected by benzoylation. The ensuing dibenzoate 14 underwent stereocontrolled opening of the aziridine ring on reaction with MeSH/BF 3 to give a thioether 15 . With benzoic acid in CHCI 3 , 10d 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 ).