Y-Butyrolactols

Optimum yields of (3-vinyl-y-butyrolactols from the Pd(II) promoted reaction of vinyl triflates with Z-but-2-en-l,4-diol (Scheme 6.33) are attained when tetra-n-butylammonium chloride is added (47]. The lactol is conveniently oxidized to the lactone with celite-supported silver carbonate. The corresponding arylbutyrolactols are obtained in high yield (70-80%) from an analogous reaction of iodoarenes with the enediol. The yields of 2-alkenyl-2,5-dihydrofurans, resulting from the Pd(0) catalysed reaction of cyclic alkynylcarbonates with acrylic esters via tandem C-C and C-0 bond forming reactions, are enhanced by the presence of tetra-n-butyl-ammonium fluoride (e.g. Scheme 6.33) (48]. 

Oxidation of l-alkene-4-ols. These substrates are oxidized by PdCl2 (catalytic) and p-benzoquinone (3 equiv.) or by CuCl/O, at 40° to y-butyrolactols (cyclic hemiacetals), precursors to y-butyrolactones.1... 

The mild conditions of photocatalysis appear well suited for the conjugate alkylation of sensitive substrates such as unsaturated aldehydes, in contrast to the high susceptibility of such substrates to 1,2 rather than 1,4 attack in thermal methods. In this case, y-butyrolactols (or lactones) have been synthesized. The organic solvent could in part be replaced by water, thus allowing the use of a hydrosoluble photocatalyst (disodium benzophenonedisulfonate (BPSS) or the sodium salt of 4-benzoylbenzoic acid). The BPSS photocatalyzed reaction of 2-hexenal in a methanol-water 1 1 mixture afforded lactol 11 (ca. l.b g, 57% yield) that was easily oxidized to the corresponding y-lactone (12, Scheme 2.5). ... 

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