EXPLORATORY INVESTIGATIONS PROBING A PREPARATIVELY VERSATILE, PYRIDINIUM SALT PHOTOELECTROCYCLIZATION-SOLVOLYTIC AZIRIDINE RING-OPENING SEQUENCE

A novel pyridinium salt photoelectrocyclization-nucleophilic bicyclic aziridine ring opening reaction sequence has been investigated in orde r to determine its preparative potential. N-Alkylpyridinium perchlorat es were found to undergo photoinduced electrocyclization upon irradiat ion in nucleophilic solvents, such as H2O and MeOH, to efficiently pro duce 6-alkyl-6-azabicyclo[3.1.0]hex-2-en-4-yl alcohols and ethers. The bicyclic aziridine photoproducts react with a number of different nuc leophiles (e.g., H2O, MeOH, AcOH, AcSH) under acid-catalyzed condition s to produce ophile-substituted)-4-(alkylamino)cyclopenten-3-yl alcoho ls and ethers. The aziridine ring opening processes are both regiosele ctive and stereoselective, yielding trans,trans-trisubstituted cyclope ntenes exclusively, apparently as a consequence of the operation of an SN2 mechanism. The effects of C-alkyl substitution on the regiochemis try of the pyridinium cation photocyclization reaction were briefly pr obed, and a method was developed to produce trans,cis-trisubstituted c yclopentenes by use of this tandem preparative sequence.