THE ZIRCONIUM-PROMOTED CARBOMETALATION OF HETEROFUNCTIONALIZED ACETYLENES
Abstract
The controlled zirconium-promoted carboalumination of acetylenes has been shown to tolerate proximal heterofunctionalities such as alcohols, sulfides, organosilanes and iodides without adverse effects on the stereo- or regiochemistry of the reaction. In some examples of heterofunctional acetylenes, an intriguing carbometalation/Friedel-Crafts type cyclization that produced 1-methyl-2-trimethylsilyl-substituted cyclic olefins was observed. A selective synthesis of 1,5-dienes was developed. The carbometalation and iodination of the alkenylalanes obtained from heterofunctionalized acetylenes stereoselectively produced the corresponding E-vinyl iodides. These difunctional vinyl iodides were very effective isoprene synthons which participated in a highly chemoselective palladium-catalyzed cross-coupling reaction with homopropargyl or homoallylic organozinc reagents to stereospecifically produce heterofunctionalized 1,5-dienes. Terpenoid products could be efficiently synthesized by repetitive cross coupling with functionalized isoprene synthons, especially if the newly incorporated synthon contained a functionality that could be directly converted to a new zinc reagent. In this manner silyl-substituted acyclic polyenes, potential precursors to cyclic terpenes such as germacrene A and cembrene A, have been made. It was also shown that the coupling of phenyl 1,3-dilithiopropynly sulfide with allylic bromides cleanly produced sulfur-substituted 1,5-enynes. The sulfur substituent can be reductively removed to give 1,5-enynes stereo- and regioselectively. A carbometalation system based on diorganozinc reagents and zirconocene diiodide was also examined. This reagent system gave products similar to the parent AlMe(,3)/Cp(,2)ZrCl(,2) carbometalation system via what appeared to be a zirconium-promoted carbozincation.
Degree
Ph.D.
Subject Area
Organic chemistry
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.