Indolizines reaction with methyl propiolates

With a change to non-polar solvent, the reaction of ylides 269 with alkynes and alkenes changed dramatically, as shown in Scheme 10. With DM AD in toluene the ylides give pyrazolopyridines 272 in good yield (91TL4977), and with methyl propiolate (MEP) give indolizines 273 (92H(33)203). The reaction with acrylates is much less clean, but the variety of products is said to be formed from a diazene intermediate, which splits to give a diradical (93H(35)851). 

Crabtree, Johnson, and Tebby55 have studied the reaction of pyridine with methyl propiolate and found that the major product is 31, high-pressure hydrogenation of which resulted in loss of the acrylic ester side chain to give indolizidin-3-one, whereas treatment with piperidine gave a product (32) believed to be the indolizine [Eq. (8)]. 

The monosubstitution products of the Friedel-Crafts reaction and of the nitration reaction have been interrelated to show that the substituent group is introduced at the same position in each case. A further correlation with the adduct (Id) from indolizine and methyl propiolate provides evidence that this is the 1-position as predicted.56 Acylation of 2-methoxycarbonyl-3-phenylcycl[3,2,2]azine (Is) takes place in the pyrrole part of the molecule.51... 

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