Diastereospecific synthesis of 2.6-dideoxy- and 2.4.6-trideoxy-sugars via hetero-diels-alder-reaction

Synthesis of 3,4-dihydro-2H-pyrans by hetero-Diels–Alder reactions of functionalized α,β-unsaturated carbonyl compounds with N-vinyl-2-oxazolidinone

Cycloadditions of 3-aryl-2-benzoyl-2-propenenitriles and 3-phenylsulfonyl-3-buten-2-one to N-vinyl-2-oxazolidinone proceed regio- and diastereoselectively yielding cis and trans diastereoisomers of 4-aryl-3,4-dihydro-2-(2-oxo-3-oxazolidinyl)-2H-pyrans in 37-65% yield. Cycloadducts cis- were the major products. Reaction of 5-arylidene-1,3-dimethylbarbituric acids with dienophile afforded mixtures of 2H-pyrano[2,3-d]pyrimidine-2,4(3H)-diones trans and products resulted from an elimination of 2-oxazolidinone, in 50-52% yield. To confirm the experimental results, semiempirical AM1 and PM3 calculations of frontier orbital energies have been performed.

Thermal/hyperbaric heterocycloaddition of 1,4-dialkoxy-1,3-dienes: the de novo (E,Z) way to sugars

1-(Z)-Alkoxy-4-(E)-methoxybutadiene derivatives have been reacted with ethylgyoxylate and diethyl ketomalonate under thermal or hyperbaric conditions. They provide, with a total regioselectivity and fair to total endoselectivities, the expected dihydropyranic cycloadducts. Three of those pseudo-glycals have been converted in a few classical steps (deprotection, reduction, and dihydroxylation) into (racemic) allose, mannose, and gullose derivatives. The order of these three steps has a direct influence on the efficiency of the transformation and determines the stereochemistry of the final sugar.

Tandem hetero diels-alder reaction: synthesis of oxygenated macrocycles

[structure: see text]. C2-symmetric, oxygenated macrocycles have been synthesized from simple acyclic precursors in a single step by a tandem hetero Diels-Alder reaction. Thermolysis and Lewis acid catalysis can effect this novel transformation. The tandem reaction product is formed in preference to the intramolecular cycloaddition product, and an explanation for this result is proposed.

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.