Oxazolidinone, chiral dioxetane synthesis

The oxazolidinone-substituted olefin Ic (Scheme 3) constitutes another fortunate substrate for the diastereoselective synthesis of a chiral dioxetane , which is of preparative value for the enantiomeric synthesis of 1,2 diols . For example, the photooxygenation of the enecarbamate Ic produces the asymmetric dioxetane 2c in >95% jt-facial diastereoselectivity. The attack of the O2 occurs from the jt face anti to the isopropyl... 

As already hinted at above, chiral dioxetanes, obtained through the highly stereoselective [2 + 2] cycloaddition of singlet oxygen to the chiral enecarbamate, provide a convenient preparation of optically active 1,2 diols as building blocks for asymmetric synthesis (Scheme 5) . Reduction of the dioxetane 2c by L-methionine, followed by release of the oxazolidinone auxiliary by NaBH4/DBU reduction, affords the enantiomerically pure like-5 diol (for additional cases, see Table 4 in Reference 19e). 

A promising unprecedented application of the chiral enecarbamates Ic in asymmetric synthesis is based on the ship-in-the-bottle strategy, which entails the oxidation of these substrates in zeolite supercages . In this novel concept, presumably dioxetanes intervene as intermediates, as illustrated for the oxidation of the chiral enecarbamate Ic in the NaY zeolite (Scheme 6). By starting with a 50 50 mixture of the diastereomeric enecarbamates (45, 3 R)-lc and (45, 3 5 )-lc, absorbed by the NaY zeolite, its oxidation furnishes the enantiomerically enriched (ee ca 50%) S -methyldesoxybenzoin, whereas the (4R,3 R)-lc and (4R,3 S)-lc diastereomeric mixture affords preferentially (ee ca 47%) the R enantiomer however, racemic methylbenzoin is obtained when the chirality center at the C-4 position in the oxazolidinone is removed. Evidently, appreciable asymmetric induction is mediated by the optically active oxazolidinone auxiliary. 

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