Peri-and regio-selectivity in cycloaddition reactions of 1-substituted pyridinium-3-oxide

1-methyl- and 1-phenylpyridinium-3-oxides [Ia and Ib] reacted with benzalacetophenone [II] to yield three types of bicyclic adducts. The first proceeded via 2 pi + 4 pi cycloaddition across the 2 6-positions of the pyridine ring to give single regioisomers in favor of endo-6-substituted azabicyclo [3.2.1] octenones [III] and [IV]. The second involved 2 pi + 8 pi, by addition across the C[4]-O, to give the dihydrofuro [2,3-c] pyridine [VII], and the involved C[2]-O to give substituted dihydrofuran V and VI. 1-[4,6-dimethylpyrimidin-2-yl] pyridinium-3-oxide [Ic] reacted with 4-nitrophenylisothiocyanate by addition across the C[2]-O to give the oxazole-2-thione derivative X. Structural assignments were deduced by elemental analysis and spectral evidence

Methylation of 3- [1-arylyhdrazono-L-threo-2,3,4-trihydroxybutyl] 6,7-dimeth yl-1H-quinoxalin-2-ones

Several N-methyl derivatives of 3-[1-arylhydrazono-L-threo-2, 3, 4- trihydroxybutyl]-6, 7-dimethyl-1H-quinoxalin-2-ones were prepared and converted to 3-[5-[acetoxymethyl]-1-arylpyrazol-3-yl]-1, 6, 7 -trimethylquinoxalin-2-ones. Upon deacetylation, compound VIII and IX gave products identical with those obtained by methylation of 3-[1- aryl-5-[hydroxymethyl]-pyrazol-3-yl]-6, 7-dimethyl-1H-quinoxalin -2- ones