EXERTING FACE-STEREOSELECTIVE SHIELDING - DESIGN OF AN ENANTIOMERIC PAIR OF CAMPHENE-BASED OXAZOLIDIN-2-ONES FOR USE AS RECYCLABLE CHIRAL AUXILIARIES IN ASYMMETRIC-SYNTHESIS

Preparative methodology is described for access to a range of enantiom erically pure oxazolidin-2-ones by chemical elaboration of naturally-o ccurring compounds (terpenes, carbohydrates) via a stereospecific intr amolecular nitrene insertion reaction. The effectiveness and limitatio ns of these reagents as chiral control elements in the form of their N -acyl derivatives for an array of asymmetric transformations is report ed. In particular, the efficiency of the spiro-oxazolidin-2-one (+)-3 obtained from (-)-camphene is highlighted by the virtually complete st ereoselection attained in such reactions as the Diels-Alder, conjugate addition, aldol, alkylation and acylation reactions. An added benefit to 3 is that its enantiomer (-)-3 is also readily accessible from (+) -camphene, thereby allowing preparative access to both enantiomeric pr oducts in a range of asymmetric manipulations. both reagents are readi ly cleaved from the newly created chiral moieties and can be recycled. This exceptional quality of asymmetric induction imparted by (+)-3 is highlighted by a concise synthesis of the tri-substituted lactone (-) -dihydroprotolichesterinic acid in 57% overall yield via consecutive s tereo-controlled 1,4-conjugate addition and syn-aldol reactions.