Dicarbonyl compounds have been prepared from bicyclic ketals in high yield under mild conditions by using aluminium chloride-sodium iodide in methylene dichloride.Although Lewis acid induced rearrangements of bicyclic ketals are an attractive method for the synthesis of natural products,' they have been little investigated. In our studies of the 6,8dioxabicyclo[3.2. lloctane skeletal system which is easily prepared from methyl vinyl k e t ~n e , ~ we have found a new synthetic route from bicyclic ketals to 1,5-dicarbonyl compounds, with potential as intermediates for 6-membered heterocycles and cyclopentane derivative^.^ Mild reagent systems such as boron trifluoride-diethyl ethersodium iodide," chlorotrimethylsilane-sodium iodide and aluminium chloride-sodium iodide were used to cleave the bicyclic ketal with interesting results.

No abstract

Stereoselective reduction and cycl ization of 6 -methyl -2propionyl-2,3d i hyd ro -4Hpyran provides brevicomin in quantitative yield as a 86:14 or a 17:83 mixture of exo and endo isomers through DIBAH reduction in ether at reflux or Zn(BH,), in the presence of ZnCI, in ether at 0 "C, respectively.

No abstract

No abstract