title: Scope and limitations of the double [4+3]-cycloadditions of 2-oxyallyl cations to 2,2'-methylenedifuran and derivatives.
abstract: The reactivity of various 2-oxyallyl cations toward 2,2'-methylenedifuran (1b), 2,2'-(hydroxymethyl)difuran (1c), 2,2'-(trimethylsilylmethylene)difuran (1d), and di(2-furyl)methanone (1e) has been explored. Difuryl derivatives 1c, 1d, and 1e refused to undergo formal double [4+3]-cycloadditions. Conditions have been found to convert 1b into meso-1,1'-methylenedi[(1R,1'S,5S,5'R)- (3) and (+/-)-1,1'-methylenedi[(1RS,1'SR,5SR,5'RS)-8-oxabicyclo[3.2.1]oct-6-en-3-one] (4) that do not require CF(3)CH(OH)CF(3) as solvent. High yields of meso-1,1'-methylenedi[(1R,1'S,2S,2'R,4R,4'S,5S,5'R)- (5) and (+/-)-1,1'-methylenedi[(1RS,1'RS,2SR,2'SR,4RS,4'RS,5SR,5'SR)-2,4-dimethyl-8-oxabicyclo[3.2.1]oct-6-en-3-one] (6) have been obtained when 1b was reacted with 2,4-dibromopentan-3-one (7h) and NaI/Cu.
authors.affiliation: Institute of Molecular and Biological Chemistry, Swiss Federal Institute of Technology, EPFL-BCH, CH-1015 Lausanne-Dorigny, Switzerland.
authors.forename: Kai Torsten
authors.initials: KT
authors.lastname: Meilert
authors.forename: Marc-Etienne
authors.initials: ME
authors.lastname: Schwenter
authors.forename: Yuli
authors.initials: Y
authors.lastname: Shatz
authors.forename: Srinivas Reddy
authors.initials: SR
authors.lastname: Dubbaka
authors.forename: Pierre
authors.initials: P
authors.lastname: Vogel