(R)-Roche ester and (S)-glycidol as chirons, the synthesis involved a highly syn-selective Lewisacidcatalyzed 6-endo-trig cyclization for the construction of the dihydropyran subunit. The lactone segment was built through a tandem NaOMe conjugate addition-lactonization reaction, and further functionalized through a sequence consisting of iodination, I−Mg exchange, and hydroxymethylation. Other key steps in
A methodology is described for the synthesis of 2,6-disubstituted dihydro[2H]pyrans through a Lewis-acidcatalyzed 6-endo-trig cyclization of β-hydroxy-γ,δ-unsaturated alcohols. Employing alkyl-substituted allylic diols and catalytic amounts of a Lewis acid, such as BF3·OEt2, the corresponding syn-pyrans are formed highly diastereoselectively and in good yields. The described process is simple to execute
An enantioselective synthesis of the antifungal natural product (+)-ambruticinS has been accomplished starting with the readily available methyl α-d-glucopyranoside, (R)-Roche ester, and (S)-glycidol as chirons, which encompassed seven of the 10 stereogenic centers of the target molecule. The remaining three centers were set by a highly diastereoselective, asymmetric cyclopropanation employing a chiral