Reaction of o-Benzyne with Tropothione Involving Biradical Processes

• Published in: Journal of organic chemistry 2007-04, Vol.72 (8), p.2832-2841
• Main Authors: Yamabe, Shinichi, Minato, Tsutomu, Ishiwata, Akihiro, Irinamihira, Osamu, Machiguchi, Takahisa
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; Heterocyclic compounds; Heterocyclic compounds with o, s, se, te hetero atom and condensed derivatives; Organic chemistry; Preparations and properties
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo062256e

A benzyne−tropothione reaction was studied experimentally and computationally. Three isomeric products were detected by a careful experiment using two benzyne sources. The three equimolar products were identified. The expected symmetry-allowed [4 + 2] or [8 + 2] cycloadduct was not detected. In order to explain the unexpected products, density functional calculations and complete active space self-consistent field (CASSCF) calculations were carried out. The benzyne is, first, added to the tropothione via one-center C−S bond formation. Then a singlet biradical intermediate is formed. In the biradical, an α hydrogen atom of the tropothione moiety is moved to the benzyne moiety. A closed-shell intermediate is generated. This allene-type intermediate is isomerized to the second intermediate. The intramolecular proton shift in the latter leads to the three products. The biradical character of the benzyne has a key role in the present reaction and was discussed in reference to other benzyne reactions.