Pyridinium e-toluenesulfonylmethylide serves as a formyl anion equivalent and, in the presence of an alcohol, undergoes 1,4-addition to N-substituted maleimides to give alkoxy-(or aryloxy)-methylenesucznimides. The protected aldehyde group can be liberated readily. Formyl anion equivalents have recently been receiving considerable attention in synthetic methodology,3 and some interesting work has been carried out to achieve 1,4addition to enones. We now report a novel one carbon donor, namely pyridinium e-toluenesulfonylmethylide (I), which adds 1,4 to &-substituted maleimides and leads to the formation of enol ethers 3. c The ylides (!, and substituted derivatives thereof) react with activated acetylenes5 and with maleic anhydride in the presence of alcohols6 to give indolizine derivatives. In the latter case, yields are very low when the pyridine ring does not bear an electronwithdrawing substituent. Reaction of 1-e-toluenesulfonylmethylpyridinium triflate (2) with Nphenylmaleimide in the presence of triethylamine in chloroform-ethanol (3:1 v/v)~ did not yield a cycloadduct. Instead, a product C1sH1sNOs ($), mJ/e 217, mp 178-179'C, was isolated (62% yield) together with 3-e-toluenesulfonyl-I-phenylsuccinimide (3; R = Ph) (5%), mp 176-177"C.a Compound 2 exhibited C=O stretching bands at 1700 and 1666 cm-' and the NMR spectrum showed the presence of an OC2H5 group, a 2H (doublet) (J_ = 2Hz) at 6 3.3, and a six proton multiplet at 6 7.3 (5 aromatic protons and one deshielded vinylic proton). These data rule out all possible structures except 2 (R = Ph, R' = OC2Hs) and 2 (or a tautomer 2). Structure 2 was ruled out by comparison of the product with an authentic sample of 2 prepared from diethyl phenylaminomethylenesuccinate.g Catalytic reduction of 2 (10% Pd-C) in ethyl acetate gave z * (100X), mp 81-82'C [NMR (CDCls) 6 7.3 (m, 5H, aromatic), 3.5 (m, 4H), 2.8 (m, 3H), 1.1 (t, 3H, Et