Benzoquinones and related compounds. Part 4. Thermolysis of the Diels–Alder adduct of 2-acetyl-5,6-dichloro-1,4-benzoquinone and cyclopentadiene: evidence for a partial retro-diene reaction
作者:Roy L. Beddoes、J. Malcolm Bruce、Harry Finch、Leslie M. J. Heelam、Ian D. Hunt、Owen S. Mills
DOI:10.1039/p19810002670
日期:——
cyclopentadiene yields, predominantly, the 1:1 Diels–Alder adduct (6) by endo-addition to the 2,3-double bond. Thermolysis of this adduct in benzene results in disproportionation to cyclopentadiene and the spiro-acetal (13); thermolysis in acetic acid also yields (13), but the major product is the dihydrobenzofuran (14), an isomer of the Diels–Alder adduct. Mechanisms for the formation of these products are
在未取代的双键处将氯加成至(2-甲基-1,3-二氧杂戊-2-基)-1,4-苯醌。随后的缩醛的烯醇化和裂解以50%的总收率得到2-乙酰基-5,6-二氯氢醌。将其氧化可得到相应的1,4-苯醌,其中环戊二烯主要通过内加成至2,3-双键生成1:1 Diels-Alder加合物(6)。该加合物在苯中的热解导致歧化成环戊二烯和螺缩醛(13);在乙酸中热裂解也能得到(13),但主要产物是二氢苯并呋喃(14),它是Diels–Alder加合物的异构体。讨论了形成这些产物的机理。