TETRA(SPIROTETRAHYDROFURANYL)CYCLOHEXANE-1,2-DIONE - STEREOCONTROLLEDSYNTHESIS AND DEFINITION OF ITS SUSCEPTIBILITY TO PHOTOISOMERIZATION

The title alpha-diketone (18) has been synthesized in stereocontrolled fashion, The ability to introduce the four contiguous spirocyclic eth er oxygens in extended trans fashion rests on the ability of the Norma nt reagent (ClMgCH2CH2CH2OMgCl) to engage in chelation control during 1,2-addition to an a-oxy substituted cyclohexanone, The successful pat hway is dependent on the ability of osmium tetraoxide to add (slowly) across the double bond of the cyclohexene precursor, The highly substi tuted 1,2-cyclohexanedione is quite sensitive to light and rearranges by means of an interesting photoisomerization process to a laterally f used pyran system, A likely mechanistic pathway for this intramolecula r isomerization is presented.