Theoretical insight into the mechanism of Pt(ІІ)-catalyzed [3+2] cycloaddition reactions of propadienyl silyl ethers with alkenyl ethers

By carrying out DFT calculations, we have performed a detailed mechanism study on the Pt(II)-catalyzed [3 + 2] cycloaddition reactions of propadienyl silyl ethers with alkenyl ethers. We calculate the mechanism proposed by Iwasawa et al. about the cycloaddition reactions of triisopropylsilyl (TIPS) 1,2-propadienyl ether (1a) with 2-methoxypropene (2a), tert-butyldiphenylsilyl (TBDPS) 1,2-propadienyl ether (1b) with 2a, and 1b with benzyl substituted alkenyl ether (2b), respectively. The calculated results show that the two reactions proceed according to similar elementary step mechanism. For the cycloaddition reaction of 1a with 2a, the products are cyclopentene derivative 3a and methylenecyclobutane derivative 4a. In contrast, for the cycloaddition reaction of 1b with 2a and 1b with 2b, due to the less electron-donating TBDPS group and the more steric repulsion between TBDPS group and the metal fragment, the predominant product is 3a.