Oxidative reactions of azines. 11. The influence of manganese dioxide on the reaction of tetrahydropyridines with formaldehyde: Synthesis and molecular structures of 3-oxa-7-azabicyclo[3.3.1]- and 6-oxa-2-azabicyclo[3.2.1]octanes

New derivatives of piperidino[4,5-d]dioxane and 3-oxa-7-bicyclo[3.3.1] nonane were obtained by the oxidatively catalysed condensation of 4-aryl-1,2,3,6-tetrahydropyridines with formaldehyde. The direction of this reaction is sharply altered in the presence of manganese dioxide to give 6-oxa-2-azabicylo[3.2.1]octan-4-one - the product of the oxidative condensation of a new type.