[reaction: seet text] Two synthetic routes to several (Z)-polyaromatic and heteroaromatic substituted vinylacetylenes are described. The nature of aryl- or heteroaryl-substituted carboxaldehyde used as starting material dictated the choice of Wittig salt employed. A very attractive way to construct polyaromatic and pyridine-containing enynes is the reaction of polyaromatic and pyridine-containing aldehydes with bromomethyltriphenylphosphonium bromide in the presence of potassium tert-butoxide followed by a Sonogashira desilylation procedure (method B).

Significance: A rapid and efficient synthesis of indolizine derivatives is presented. The silylated enyne pyridine and quinoline precursors, obtained by a Wittig-Sonogashira sequence, undergo an unexpected electrocyclic ring closure, which is triggered by a fluoride-mediated desilylation reaction under mild conditions. A plausible mechanism is proposed on the basis of analysis of deuterium labelling experiments.Comment: The indolizine ring constitutes the core of a class of natural products (e.g.). The present synthesis appears to be a general and efficient method for the construction of fused indolizines from readily accessed starting materials. Furthermore, the use of other O, N, and S nucleophiles for the preparation of functionalized systems may be anticipated. N O 1) t-BuOK, N 2) TMS-CCH, Et 3 N PdCl 2 (Ph 3 P) 2 , CuI TMS CsF ROH N RO up to quant. yield N N RO electrocyclic ROH R = Alk, All, Bn R-O N OMe D D 87%, MeOD was used (Ph 3 P + CH 2 Br)Br -SYNFACTS Contributors: Victor Snieckus, Oleg M. Demchuk Synfacts 2006, 1, 0025-0025 P u b l i s h e d o n l i n e : 0 5 . 0 1 .

For Abstract see ChemInform Abstract in Full Text.

Alkenes Q 0083Practical Synthesis of (Z)-Polyaromatic and Heteroaromatic Vinylacetylenes. -Two alternative and general pathways are developed. The synthetic utility of these methods is illustrated by transformation of electron-rich and electron-deficient heteroaromatic as well as aromatic carboxaldehydes to their (Z)-vinylacetylenes in good to excellent yields. -(HAYFORD*, A.; KALOKO, J. J.; EL-KAZAZ, S.; BASS, G.; HARRISON, C.; CORPREW, T.; Org. Lett. 7 (2005) 13, 2671-2673; Dep. Chem., East Carolina Univ., Greenville, NC 27858, USA; Eng.) -Y. Steudel 44-085