title: Highly regioselective construction of spirocycles via phosphine-catalyzed [3 + 2]-cycloaddition.
abstract: A direct entry to spirocycles with low to moderate regioselectivity was achieved by triphenylphosphine-catalyzed [3 + 2]-cycloaddition of active exo-methylenecycles (1) and ethyl 2,3-butadienoate (2). The regioselectivity of the reaction was greatly improved by using the bulky tert-butyl ester of the 2,3-butadienoate (5). The regioselectivity of the reaction was further enhanced by using the tert-butyl 2-butynoate as the substrate. This protocol provided an efficient entry to the skeleton of spirocarbocycles, especially spiro[4.n]alkanes.
authors.affiliation: State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Lu, China.
authors.forename: Yishu
authors.initials: Y
authors.lastname: Du
authors.forename: Xiyan
authors.initials: X
authors.lastname: Lu
authors.forename: Yihua
authors.initials: Y
authors.lastname: Yu