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.
Highlights
The synthesis of hydrogenated pentalene ketone intermediates has found applications in obtaining new drugs, of which the best known are carbacyclin [1] and isocarbacyclin [2,3,4,5,6,7,8] analogues, cioctol [9]and a few antibacterial [10] and antitumor natural products [11,12]
The standard key intermediate I has a symmetric ketone for linking the α-side chain by a Wittig
We describe the synthesis of the ketone-octahydropentalenes α-Side chain of types V and VI useful for obtaining new carbacyclin analogues
Summary
The synthesis of hydrogenated pentalene ketone intermediates has found applications in obtaining new drugs, of which the best known are carbacyclin [1] and isocarbacyclin [2,3,4,5,6,7,8] analogues, cioctol [9]. In the synthesis of isocarbacyclin analogues, a few pentalene intermediates with different structures have been used to build the α-side chain (Figure 1). Thispaper, paper,we wedescribe describe the ketone-octahydropentalenes α-side chain by different methods [21,22,23,24]. Of for new carbacyclin and isocarbacyclin analogs requires new key intermediate octahydropentalene ketones. We describe the synthesis of the ketone-octahydropentalenes α-Side chain of types V and VI useful for obtaining new carbacyclin analogues
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