Indolizyl-5-lithium anions react with succinic and phtalic anhidrides giving 1,4-keto acids, with oxallyl chloride giving 1,2-diketone, and with ethyl pyruvate giving 1,2-hydroxyacid. However, with α-halocarbonyl compounds, they react in different ways, forming the products of selective bromination at C-5 (with α-bromo ketones and esters of α-bromo acids) and 5-chloroacetyl indolizines.
2-tert-Butyl-5-iodoindolizine underwent Sonogashira reaction with acetylenes in the presence of dichlorobis(triphenylphosphine)palladium, copper(I) iodide, and triethylamine in acetonitrile to give to the corresponding 5-ethynylindolizines in high yields; 5-iodo-2phenylindolizine and 5-bromo-2-tert-butylindolizine did not undergo the reaction. Several structures were characterized by X-ray. The 5ethynylindolizines did not undergo cyclization to give cycl[3.2.2]azines.
Sonogashira Reaction of the Indolizine Ring. -2-Tert-butyl-5-iodoindolizine is successfully coupled with aryl and alkylacetylenes as well as trimethylsilylacetylene. A corresponding transformation of 5-bromo or 2-phenyl substituted substrates fails as well as an attempted cyclization of the products to cyclo[3.2.2.]azines. -(SHADRIN, I. A.; RZHEVSKII, S. A.; RYBAKOV, V. B.; BABAEV, E. V.; Synthesis 47 (2015) 19, 2961-2964, http://dx.
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