title: TiCl(4)-promoted Baylis-Hillman reactions of substituted 5-isoxazolecarboxaldehydes with cycloalkenones).
abstract: The Baylis-Hillman (BH) reaction of substituted 5-isoxazolecarboxaldehydes with cyclohexenone in the presence of TiCl(4) invariably lead to the formation of hemiacetals beside the BH adducts. A similar reaction in the presence of DABCO, DBU, or 3-HQN yielded minor quantities of phenols in addition to the usual BH adducts. Similar to 5-isoxazolecarboxaldehydes, the TiCl(4)-mediated BH reaction of cyclohexenone with various benzaldehydes also furnishes hemiacetals in considerable yields. The reaction mechanism involving the formation of alpha-chloromethyl enone as an intermediate has been proposed. The synthesis of hemiacetals 5 and 14 from compound 4 in the presence of cyclohexenone and cyclopentenone, respectively, under acidic conditions indicates that enolization and aromatization of the cyclohexene ring are the key steps in the reaction mechanism.
authors.affiliation: Medicinal ChemistryDivision, Central Drug Research Institute, Lucknow 226 001, India.
authors.forename: Arundhati
authors.initials: A
authors.lastname: Patra
authors.forename: Sanjay
authors.initials: S
authors.lastname: Batra
authors.forename: Bhawani S
authors.initials: BS
authors.lastname: Joshi
authors.forename: Raja
authors.initials: R
authors.lastname: Roy
authors.forename: Bijoy
authors.initials: B
authors.lastname: Kundu
authors.forename: Amiya P
authors.initials: AP
authors.lastname: Bhaduri