Palladium(0)-assisted synthesis of C-glycopyranosyl compounds.

Tetrakis(triphenylphosphine)palladium(0) effects the regio- and stereo-selective alkylation of 2-acetoxy-5,6-dihydro-2H-pyrans and 1-S-acetyl-1-thiohex-2-enopyranosides. Use of stabilized carbanions resulted in the formation of alkylated dihydropyrans with net retention at the oxygen-bearing carbon atom. Examples include the preparation of 2-[acetamidobis(ethoxycarbonyl)methyl]-5,6-dihydro-2H-pyran, 2-[acetamidobis(methoxycarbonyl)methyl]-6-ethoxy-5,6-dihydro-2H-py ran, and 2-[acetamidobis(methoxycarbonyl)methyl]-6-methoxymethyl-5,6-dihydr o-2H- pyran. Use of nonstabilized carbanions, such as arylzinc chlorides, resulted in the formation of alkylated dihydropyrans and C-glycosyl compounds with net inversion at the oxygen-bearing carbon atom. Examples include the preparation of 2-[(6-ethoxy-5,6-dihydro-2H-pyranyl)methyl]-4,4-dimethyl-2-oxazoli ne, trans-methoxymethyl-2-phenyl-5,6-dihydro-2H-pyran, trans-methoxymethyl-2-vinyl-5,6-dihydro-2H-pyran, trans-2-[2,2-bis(ethoxy)ethyl]-6-methoxymethyl-5,6-dihydro-2H-pyran, (4,6-di-O-methyl-2,3-dideoxy-alpha-D-erythro-hex-2-enopyranosyl)be nzene, (2,3-dideoxy-4,6-di-O-methyl-beta-D-erythro-hex-2-enopyranosyl)ben zene, 1-(2,3-dideoxy-4,6-di-O-methyl-alpha and -beta-D-erythro-hex-2-enopyranosyl)naphthalene, 4-(2,3-dideoxy-4,6-di-O-methyl-alpha- and -beta-D-erythro-hex-2-enopyranosyl)toluene, and 1-(2,3-trideoxy-4-O-methyl-alpha-L-erythro-hex-2-enopyranosyl)naph thalene.