title: Radical cyclization by ipso substitution of the methoxy group: considerable effect of HMPA on samarium-mediated cyclization.
abstract: Alkyl radicals generated by treatment of thiocarbamates of conformationally favorable 3-alkyl-3-arylpropan-1-ols with tris(trimethylsilyl)silane and AIBN efficiently undergo intramolecular ipso substitution of the methoxy group, yielding the corresponding cyclized products. In contrast, either conformationally favorable or flexible 1-arylalkan-3- or 4-ones easily cyclize into five- or six-membered condensed rings by treatment with SmI(2) via ketyl radical intermediates. The addition of HMPA as cosolvent dramatically changes the cyclization mode of the SmI(2)-induced reaction, and the para-cyclization products are exclusively formed. This "HMPA effect" can be rationalized by the strong chelating ability of HMPA with the samarium atom.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka 565-0871, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ohno
authors.forename: Ryutaro
authors.initials: R
authors.lastname: Wakayama
authors.forename: Shin-ichiro
authors.initials: S
authors.lastname: Maeda
authors.forename: Hiroki
authors.initials: H
authors.lastname: Iwasaki
authors.forename: Mitsuaki
authors.initials: M
authors.lastname: Okumura
authors.forename: Chuzo
authors.initials: C
authors.lastname: Iwata
authors.forename: Hidenori
authors.initials: H
authors.lastname: Mikamiyama
authors.forename: Tetsuaki
authors.initials: T
authors.lastname: Tanaka