1.2- Dioxetanes, synthesis

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... 

Dioxetan-3-ones spectroscopy, 7, 455 synthesis, 7, 469, 476 thermal reactions, 7, 459... 

The recently discovered preparative methods for the synthesis of 1.2-dioxetane derivatives (see Section V.) have made these compounds and their chemiluminescent decomposition the subject of especially intensive study. 

Enamines which cannot undergo ene-like reactions add efficiently to singlet oxygen. The intermediate dioxetane can be cleaved under mild conditions to afford a ketone (and an amide). Such a sequence has been applied in a synthesis of testosterone (6.18) 624). 

Section II covers the synthesis of the cyclic peroxides with medium ring size from 5 to 7. Section HI covers the synthesis of 1,2,4-trioxanes. Classification in sub-sections and sub-sub-sections is done according to the type of reaction by which the cyclic peroxide system is formed. Syntheses of dioxirans, 1,2-dioxetanes, trioxolanes (ozonides), tetrox-anes, and macrocyclic peroxides are not discussed in this review. 

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. 

Recently, the synthesis has been reported of the novel bicyclic dioxetanes 22a-c , which possess a remarkable chemiluminescence efficiency in aqueous media. Of the dioxetanes 22a-c with the 3-hydroxy-4-isoxazolylphenyl functionality, the derivative 22a is the most suitable On triggering by NaOH in water, the dioxetane 22a displays the highest CIEEL yield (0.24 at 25 °C), whereas the efficiency of componnds 22b and 22c is much lower (0.064 and 0.015, respectively). Nevertheless, the latter are still snfficiently efficient triggerable dioxetanes and quite adequate for their use in aqneons media. Snch unprecedented results definitely merit further exploration. 

In the present chapter, we have considered the main recent developments in dioxetane studies. Our incentive to concentrate on the contemporary facets of dioxetane chemistry was to assure the reader that interest in these unique cyclic peroxides has not subsided since their discovery about 35 years ago. Particularly the last decade has witnessed impressive advances in this fascinating field, from both the mechanistic and applied points of view. Moreover, a novel feature of dioxetane chemistry pertains to harnessing them as building blocks in asymmetric synthesis, hardly thought feasible about a decade ago. 

A qualitative leap in mechanistic CL research was achieved in the late sixties and early seventies of last century with the synthesis of the first 1,2-dioxetanes (1) and... 

The synthesis of A-methylacridan dioxetane derivatives would be very promising for analytical application as chemiluminescence probes. Despite the high quantum yields... 

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

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