Pentane-1,5-diols, cyclization

Barker et al. have demonstrated a vigorous benzyloxy-group participation for the ethanolysis of 4-0-benzyl-1-0-toluene-p-sulphonyl-pentane-l,4-diol to give 2-methyltetrahydrofuran, benzyl ethyl ether, and toluene- -sulphonic acid. Cyclization to 1,4-anhydropentitol deriv-... 

Many examples of the synthesis of tetrahydropyrans are based on the cyclization of 1,5-diols and compounds which can provide a similar electrophilic site for ring closure. Thus, pentan-l,5-diols can be quantitatively cyclized to the pyran in the presence of BuSnCl3 (88G483). 

Acetonization of the dialcohol 337 led to 338a in 73% yield. Less efficient was the cyclization of 337 with carbonyldiimidazole therefore, dioxocinone 338b, even under rather forcing conditions, was obtained in only 29% yield (Equation 43) <2005CEJ6629>. Another example of cyclization of dialcohols, with insertion of a carbon unit, to 1,3-dioxocins, although in poor yield, was furnished by pentane-1,5-diol and (5, (l-difluoro-a-phenylvinyl sulfide <1995H(41)641>. 

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