DEFINITION OF SEVERAL CONTROL ELEMENTS RELEVANT TO THE STEREODEFINED SERIAL ELABORATION OF BELTED POLY(SPIROTETRAHYDROFURANS) FITTED WITH ACYCLOHEXANE CORE

The stereochemistry of the condensations of 2-cyclohexenones, alpha-ar ylidenecyclohexanones, and alpha-(tert-butyldimethylsiloxy)cyclohexano nes carrying one or two (both syn and anti) spirotetra-hydrofuran unit s adjacent to the carbonyl with allyl organometallics (especially indi um) and with the Normant reagent (ClMgO(CH2)(3)MgCl) is described. Goo d levels of anti stereoselection are observed in the alpha-arylidene s eries. Subsequent cyclization generates a second (or third) tetrahydro furan ring possessing trans vicinal oxygens. Useful levels of matched and mismatched diastereoselection are also attainable by prior alpha-o xygenation, The intrinsic differences in diastereomer production betwe en indium and magnesium organometallics are highlighted. A clear disti nction regarding the anticipated direction of stereoselectivity is mad e on the grounds of chelation capabilities and the intra- or intermole cularity of carbon-carbon bond formation. Finally, the two protocols t hat are described in detail are shown to be iterative, a feature that augurs well for ultimately accessing the eight possible hexaspirocyclo hexanes in an efficient and stereocontrolled manner.