Synthesis and dimerization of two cross-conjugated trienes: 3-methylene-1,4-pentadiene and 1,2,3-trimethylenecyclohexane
作者:Walter S. Trahanovsky、Kenneth A. Koeplinger
DOI:10.1021/jo00043a032
日期:1992.8
3-Methylene-1,4-pentadiene (8) and 1,2,3-trimethylenecyclohexane (10) are prepared in moderate to high yields in good purity by the flash vacuum pyrolysis of 1,5-diacetoxy-3-(acetoxymethyl)pentane (12) and 1,2,3-tris(acetoxymethyl)cyclohexane (17), respectively. Triene 8 dimerizes cleanly at a moderate rate in benzene at 95-degrees-C to give only one major product, [4 + 2] dimer 1,4,4-trivinylcyclohexene (13). Triene 10, the conformationally restricted all cisoid analog of 8, dimerizes more rapidly in benzene at 95-degrees-C to give only one major dimer, a [4 + 2] dimer (21). It is concluded that the dimerization proceeds by a two-step mechanism: rate-determining attack at the middle methylene group to form a resonance-stabilized diradical intermediate followed by rapid closure of the diradical to give a [4 + 2] dimer.
Pyrolysis of Esters. III. Synthesis of 2-Vinylbutadiene<sup>1,2</sup>