1,3-DIPOLAR CYCLOADDITION REACTIONS OF YLIDES FORMED FROM PYRIDINES AND DICHLOROCARBENE

Article abstract of DOI:10.1007/BF00472551

Pyridinium dichloromethylides, generated from substituted pyridines and dichlorocarbene, react endo-stereoselectively with dimethyl maleate to give substituted 3,3-dichloro-1,2,3,8a-tetrahydroindolizine-1,2-dicarboxylic acid dimethyl esters; the latter compounds are readily dehydrochlorinated and dehydrogenated to give the corresponding indolizine derivatives.Reaction of 3-substituted pyridines with dichlorocarbene and dimethyl maleate leads predominantly to the formation of 8-substituted indolizines.Cycloaddition of 4-picolinium dichloromethylide to unsymmetrical dipol arophiles occurs regioselectively.The observed selectivity in these reactions is consistent with predictions made on the basis of PMO theory.