Synthesis chiral dioxetanes

The contemporary trends of dioxetane chemistry include a number of fundamental and applied aspects. The fundamental aspects encompass the stereoselective synthesis and the transformations of novel chiral dioxetanes, as well as the mechanistic studies on the thermal, electron-transfer-induced and catalytic dioxetane decomposition. The emphasis lies on the elucidation of the excited-state generation in these chemiluminescent processes. 

II. STEREOSELECTIVE SYNTHESIS OF CHIRAL DIOXETANES AND THEIR TRANSFORMATIONS... 

The past decade has seen significant achievements in stereoselective synthesis, with some pertinent developments also in dioxetane chemistry. Herein, we consider the most recent and prominent advances in the stereoselective preparation of chiral dioxetanes and their transformation into building blocks for asymmetric 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). 

Chiral catalysts, asymmetric metal-catalyzed suHoxidations, 478-85 Chiral 1,2-dihydronaphthalenes, photooxygenation, 265-6 Chiral dioxetanes, stereoselective synthesis, 1173-8... 

Semen, reactive oxygen species, 612 Sensorial quaUty appreciation, oxidation stabihty, 664 Semm protein oxidative damage, 614 see also Human seram Sesquiterpenes, stractural chemistry, 133-6 SET see Single electron transfer Sharpless epoxidation, allylic alcohols, 789 Shelf durability, peroxide value, 656 Ship-in-the-bottle strategy, chiral dioxetane synthesis, 1176-7... 

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. 

A novel properly of an electronically excited molecule can be chirality that exists only because of photoexcitation. Miesen, F. W. A. M. Wollersheim, A. P. P. Meskers, S. C. J. Dekkers, H. P. J. M- Meijer, E. W. /. Am. Chem. Soc. 1994,116,5129 reported the synthesis of optically pure 3-( n,Ji )-(lS,6R)-bicyclo[4.4.0]decane-3,8-dione, which is chiral only in the excited state. The chirality was detected in the circular polarization of chemiluminescence associated with its synthesis from an optically active 1,2-dioxetane precursor. 

In addition, silver-catalyzed asymmetric aza-Diels-Alder reactions provide a useful route to optically active nitrogen-heterocyclic compounds such as piperidines or pyrid-azines. Substituted dihydrobenzofurans can also be enantioselectively prepared through silver-promoted allylation of aldehydes. Other types of silver-mediated cyclizations can also be used in the synthesis of tetrahydrofnrans, tetrahydropyrans, 1,2-dioxetanes, 1,2-dioxolanes, medium-sized lactones, dihydroisoqninolines, and so on. Silver salts can also be used as cocatalysts with other transition metals. Unique activity was observed for these silver-based systems in several cases. Conseqnently, the use of silver can enrich several available heterocyclization methods, and fnrther developments in the application of chiral silver complexes will hopefnlly appear in the near future. 

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