Tetracyclo[2.2.0.02,6.03,5]hexane

Katz and Acton's original synthesis of prismane(Tetracyclo[2.2.0.02,6.03,5]hexane) starts from benzvalene (1) and 4-phenyltriazolidone (2), which is a strong dienophile. The reaction is a stepwise Diels-Alder like reaction, forming a carbocation as intermediate. The adduct (3) is then hydrolyzed under basic conditions and afterwards transformed into a copper(II) chloride derivative with acidic copper(II) chloride. Neutralized with a strong base, the azo compound (5) could be crystallized with 65% yield. The last step is a photolysis of the azo compound. This photolysis leads to a biradical which forms prismane (6) and nitrogen with a yield of less than 10% (in Katz and Acton's work, 1.8%, but subsequently improved).^[1]

[1]Katz T. J.; Acton N. (1973). "Synthesis of Prismane".Journal of the American Chemical Society.95(8):2738–2739.Bibcode:1973JAChS..95.2738K.doi:10.1021/ja00789a084