Hydroboration-Oxidation of (±)-(1α,3α,3aβ,6aβ) -1,2,3,3a,4,6a-Hexahydro-1,3-pentalenedimethanol and Its O-Protected Derivatives: Synthesis of New Compounds Useful for Obtaining (iso)Carbacyclin Analogues and X-ray Analysis of the Products

Abstract

Hydroboration-oxidation of 2α,4α-dimethanol-1β,5β-bicyclo[3.3.0]oct-6-en dibenzoate (1) gave alcohols 2 (symmetric) and 3 (unsymmetric) in ~60% yield, together with the monobenzoate diol 4a (37%), resulting from the reduction of the closer benzoate by the intermediate alkylborane. The corresponding alkene and dialdehyde gave only the triols 8 and 9 in ~1:1 ratio. By increasing the reaction time and the temperature, the isomerization of alkylboranes favours the un-symmetrical triol 9. The PDC oxidation of the alcohols gave cleanly the corresponding ketones 5 and 6 and the deprotection of the benzoate groups gave the symmetrical ketone 14, and the cyclic hemiketal 15, all in high yields. The ethylene ketals of the symmetrical ketones 11 and 13 were also obtained. The compounds 5, 6, 11, 13, 14 could be used for synthesis of new (iso)carbacyclin analogues. The structure of the compounds was established by NMR spectroscopy and confirmed by X-ray crystallography.

Trifluoroacetylation of Alcohols During NMR Study of Compounds with Bicyclo[2.2.1]heptane, Oxabicyclo[3.3.0]octane and Bicyclo[3.3.0]octane Skeleton

“…14.NMR spectra of the compound 12a and of the bis-trifluoroacetylated compound 12c. The un-symmetric triol 12 was esterified with trifluoroacetic anhydride in TFA (in NMR tube) and the complete esterification proceeded in 4 h. The signals of the bis-triflouroacetylated compound 12c are described below: 1 [20]).…”