Methyleneketenes and methylenecarbenes. I. Formation of arylmethyleneketenes and alkylideneketenes by pyrolysis of substituted 2,2-Dimethyl-1,3-dioxan-4,6-diones
Flash vacuum pyrolysis (430�) of 5-benzylidene-2,2-dimethyl-1,3-dioxan- 4,6-diones gives benzylidene-ketenes which dimerize to form 2,4- bis(benzylidene)cyclobutane 1,3-diones. Diphenylmethylene-,t- butylmethylene- and isopropylidene-2,2-dimethyl-1,3-dioxan-4,6-diones similarly give the substituted methylene ketenes which dimerize to form 2,4-bis(diphenylmethylene)-, 2,4-bis(t-butylmethylene)- and 2,4- bis(isopropylidene)-cyclobutane-1,3-dione respectively. Infrared measurements on the pyrolysis products kept at liquid nitrogen temperature showed absorption near 2100 cm-1 which was attributed to the methyleneketenes. Reaction of the pyrolysates of ethylidene- and isobutylidene-2,2-dimethyl-1,3-dioxan-4,6-diones with aniline vapour yielded but-3-enanilide and 4-methylpent-3-enanilide respectively.