Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Various vinylallenes were synthesized by conjugate cuprate additions to acetylenic Michael acceptors. Thus, 1,6-addition reactions with 2-en-4-ynoates 1, 3, and 5a, respectively, furnished vinylallenes 2, 4, and 7 after regioselective electrophilic capture of the allenyl enolates formed. Likewise, 1,8-addition to 2,4-dien-6-ynoates 8a and 10 gave the vinylallenes 9 and 11, whereas the 1,10-addition of Me2CuLi to 2,4,6-trien-8-ynoate 12 provided allene 13, and the analogous 1,12-addition to 2,4,6,8-tetraen-10-ynoate 14 furnished the polyene 15. These vinylallenes are valuable dienophiles in regio- and stereoselective Diels-Alder reactions, as evidenced by the formation of the cycloaddition products 16-24. In the presence of Lewis acids, vinylallene 4a presumably rearranges to a cyclopentadiene derivative which then forms the cycloadducts 25 and 26.
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