Transformations of unsaturated acyclic sugars into enantiomerically pure norbornene derivatives

The C7 acyclic unsaturated-sugar ester 1, derived from L-arabinose, and its enantiomer serve as convenient dieneophiles for chirality transfer for synthesis of optically pure carbocyclic derivatives through cycloaddition reactions. Reaction of 1 with cyclopentadiene may be controlled to give preparative access to the 5,6-disubstituted norbornene adducts 4a, 5a, and 7a, according to the conditions used. The distribution of the four possible isomeric products from this cycloaddition was quantitated, and the effect of substitutional variation on the precursor dienophile 1 was also examined. Adducts 4a and 5a were transformed into such substituted carbocycles of known absolute configuration as the methyl esters (11 and 12) of norbornene (bicyclo[2.2.1]hept-2-ene)-6-carboxylic acid and nortricyclane (tricyclo[2.2.1.0(2,6)]heptane)-3-carboxy acid in optically pure form, specifically through decarbonylation reactions using RhCl(PPh3)3 (Wilkinson's complex) and [Rh(dppp)2]Cl[dppp = Ph2P(CH2)3PPh2]. The optical purity of 12 was established by the use of a chiral lanthanide shift-reagent.