Novel Approaches to Stereo- and Enantioselective Syntheses of Versatile Intermediates via Unsaturated Organometallics of Main Group Metals

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This renewal grant is being funded by the Organic Synthesis Program. Dr. Zweifel is continuing his fruitful development of organometallic regents that contain unsaturation(carbon-carbon double or triple bonds). These reagents have the potential to provide new routes to the unusual structures found in some pheromones in some pests and in some compounds used by sea organisms to communicate with each other. The specific aims of the research are: (a) elaboration of the ethynyl and enol ether groups of 1-methoxybut-1-en-3-yne into substituted five- and six-membered ring lactones, acylsilanes, 1,3-diynes, and yne-1,2-propadienes. The special merit of this lies in its potential for transforming an inexpensive starting material into diverse and synthetically attractive derivatives; (b) exploitation of the three potentially nucleophilic centers of 1-(trimethylsilyl)-1,3-diyne derived mono- and bis(stannyl) enynes for syntheses of beta-alkylidene-gamma-butyrolactones and beta, gamma-unsaturated valerolactones. The biological activities of these hitherto not readily accessible systems remain to be explored. The palladium-catalyzed cross-coupling reactions of stannyl enynes with electrophiles will be investigated to gain access to stereodefined conjugated ene-dienes, yne-dienes, and ene-diynes whose structural features occur in many fungal metabolites, which possess antibiotic activity; (c) preparation of chiral 3-borolenes and investigation of their use as templates for effecting acyclic stereocontrol with concomitant control of absolute stereochemistry in syntheses of quaternary carbon centers and compounds having three consecutive stereogenic centers.