Dimethyl ethoxycarbonylmethylene

Ethoxycarbonylmethylene-3//-pyrrolizine (32), prepared from pyr-rolizin-3-one with ethoxycarbonylmethylenetriphenylphosphorane,34-36 reacted slowly with dimethyl acetylenedicarboxylate to give a mixture of products from which the [3,2,2]azine ly was isolated in 12%lyield.37... 

A rather general feature of methylenecyclopropanes with double-bond systems in the a-position to the endocyclic methylene is the rearrangement to products where the unsaturated substituent is not located at the exocyclic methylene group. Examples are 1,1-dimethyl-2-methylene-3-vinylcyclopropane (Table 1, R = R = R = H R = R" = Me R = CH = CH2) and ethyl l,2,2-trimethyl-3-methylenecyclopropanecarboxylate (Table 1, R = R = H R = R = R = Me R = C02Et) which isomerized to l-(l-methylethyl-idene)-2-vinylcyclopropane and ethyl l-methyl-2-(l-methylethylidene)cyclopropanecar-boxylate, respectively. The only reported exceptions are ethyl 2,2-dimethyl-3-methylenecyclo-propanecarboxylate (Table 1, R = R = R = H R = R" = Me R = C02Et), which formed both 2-(ethoxycarbonylmethylene)-l,l-dimethylcyclopropane and ethyl 2-(l-methyl-ethylidene)cyclopropanecarboxylate, and l-(l-methylethylidene)-2-phenylcyclopropane (Table 1, R = R = Me R = Ph R" = R = R = H), which was converted into (Z)- and ( )-2-benzylidene-l,l-dimethylcyclopropane (20 and 25 /o, respectively), upon heating to 200"C. ... 

The ring transformation to /V-melhylpyrrole 320 as a minor product occurred from the 2-methyl salt 75j on reaction with dimethyl-(2-ethoxycarbonylmethylene)sulfu-rane (84CJC1580, Schemes 106, 108). 

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