Dioxetanes chiral

The steering effect of the hydrogen bonding was applied to a highly diastereose-lective dioxetane formation from a chiral allylic alcohol (Scheme 21) [110]. 

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). 

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. 

Unquestionably, the advantage of the present methodology is that the intermediary dioxetane serves as a vehicle to place the chiral inductor (the oxazolidinone auxiliary) and the racemic substrate to be resolved (the methyldesoxybenzoin) in one and the same zeolite supercage. These represent optimal conditions for efficacious asymmetric induction, a novel application of chiral dioxetanes which merits further elaboration. 

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... 

The optically active 1,2-dioxetane of 2,4-adamantanedione (89) was synthesized. Thermal activation of 89 yielded chemiluminescence (Xmax = 420 nm characteristic of ketone fluorescence), pointing to intermediate 90 which is chiral only in its excited state due to the out-of-plane geometry of one of the two carbonyl groups. However, circular polarization of chemiluminescence measurement of 90 has not detected optical activity at the moment of emission. The authors have concluded that fast, relative to the lifetime of ketone singlet excited state, intramolecular n, it energy transfer caused racemization of 90196. 

---