title: Asymmetric synthesis of gem-difluoromethylenated linear triquinanes via cascade gem-difluoroalkyl radical cyclization.
abstract: An asymmetric synthesis of gem-difluoromethylenated linear triquinanes is described exploiting the synthetic utilities of PhSCF2TMS (5) as a "(•)CF2(-)'' building block. The strategy involves fluoride-catalyzed nucleophilic addition of PhSCF2TMS (5) to chiral ketocyclopentenes 6 to provide silylated adducts 9 or alcohol derivatives 10 and 11. Subsequent cascade radical cyclization of the gem-difluoroalkyl radical generated from silylated adducts 9 or alcohols 10 and 11 afforded gem-difluoromethylenated linear triquinanes 16 as an approximate 1:1 mixture of two diastereomers (16A and 16B). Alternatively, a convenient asymmetric synthesis of gem-difluoromethylenated linear triquinanes 16A can be accomplished by oxidation of 16a (R = H) to provide ketotriquinane 17 followed by a highly stereoselective nucleophilic addition to 17 employing DIBAL, NaBH4, and various Grignard reagents.
authors.affiliation: Center of Excellence for Innovation in Chemistry (PERCH-CIC) and Department of Chemistry Faculty of Science, Mahidol University , Rama VI Road, Bangkok 10400, Thailand.
authors.forename: Watcharaporn
authors.initials: W
authors.lastname: Thaharn
authors.forename: Darunee
authors.initials: D
authors.lastname: Soorukram
authors.forename: Chutima
authors.initials: C
authors.lastname: Kuhakarn
authors.forename: Patoomratana
authors.initials: P
authors.lastname: Tuchinda
authors.forename: Chaveng
authors.initials: C
authors.lastname: Pakawatchai
authors.forename: Saowanit
authors.initials: S
authors.lastname: Saithong
authors.forename: Vichai
authors.initials: V
authors.lastname: Reutrakul
authors.forename: Manat
authors.initials: M
authors.lastname: Pohmakotr