Selenium-directed stereoselective [2 + 2] cycloaddition reactions promoted by Lewis acids: a novel zwitterionic intermediate
摘要:
The reaction of (trimethylsilyl)vinyl selenide 1 and (trimethylsilyl)allenyl selenide 2 with vinyl ketones 3a-c in the presence of a Lewis acid gave cyclobutane derivatives stereoselectively. The reaction of 1 and 3a-c with SnCl4 was quenched either with Et3N to give cyclobutanes 4a-c or with H2O to give acylsilanes 11a-c. The formation of both products is explained in terms of a zwitterionic intermediate. The cis relationship between the phenylseleno group and the carbonyl group of 4a-c is rationalized by consideration of a combination of secondary-orbital interactions and steric effects in the early stage of intermediate formation.
The reaction of (trimethylsilyl)vinyl selenide 1 and (trimethylsilyl)allenyl selenide 2 with vinyl ketones 3a-c in the presence of a Lewis acid gave cyclobutane derivatives stereoselectively. The reaction of 1 and 3a-c with SnCl4 was quenched either with Et3N to give cyclobutanes 4a-c or with H2O to give acylsilanes 11a-c. The formation of both products is explained in terms of a zwitterionic intermediate. The cis relationship between the phenylseleno group and the carbonyl group of 4a-c is rationalized by consideration of a combination of secondary-orbital interactions and steric effects in the early stage of intermediate formation.