This report describes the detailed conformational analysis and synthesis of a series of phthalazine phosphodiesterase-type (IV) (PDE IV) inhibitors bearing either mono- or dichloro 4-methylenepyridine at the 'down' position of the phthalazine nucleus or differentheterocycles at the 'top' position 4 of the phthalazine moiety. Both the mono- and dichloro 4-methylenepyridine units linked at carbon C1