Endoperoxides chiral

Chiral endoperoxides, synthesis, 260, 261 Chiral hydroperoxides aUyhc alcohol asymmetric epoxidation, 401-6, 407-9... 

In the case of chiral base catalysis of the E2 elimination, enantioenriched 7-hydroxyenones from the corresponding endoperoxides were obtained <2006JA12658> in fact, a one-pot asymmetric 1,4-dioxygenation of 1,3-cyclohepta-diene by sequential reaction with singlet oxygen and 5 mol% chiral catalyst provided the 7-hydroxyenones 80 in 90% yield and 92% ee (Scheme 18). 

Gerdil et al. reported two examples involving the solid-gas reactions of inclusion complexes of tri-o-thymonide with alkene or epoxycyclopentanone. The complex 5 crystallized in /T3 2, and the reaction with singlet oxygen gave endoperoxide 6 however, the [other hand, the reaction of chiral crystals of the complex 7 with hydrogen chloride gave two products 8 and 9, ees of which were 9% and 22%, respectively. [13]... 

The most prevalent base-catalyzed reaction of an endoperoxide is the Kornblum-DeLaMare decomposition [97a] which leads to a hydroxy ketone by removal of a proton from the carbon adjacent to the peroxy linkage [9b,90b,97], The formation, in a basic solvent as acetone, of hydroxyfuranones 69 (Sch. 38) in the photo-oxygenation of a,a -unsubstituted furans might occur via a similar rearrangement [60e]. Attempts to induce asymmetry in endoperoxides with enantiotopic hydrogens or with chiral bases have led to moderate success [98]. The Et3N-catalyzed rearrangement of substituted cycloheptatriene endoperoxides 92 leads to... 

The stereoselectivity of the allylic hydroperoxidation also depends on se eral factors. With chiral allylic alcohols or allylic amines 200, a hydrogen is developed between ]02 and the vicinal hydroxyl or amino group. The fac differentiation results from an approach of 102 in the transition state that mi mizes 1,3-allylic strain. 201 and 202 can be obtained with a diastereoisome excess higher than 90% in CCI4. As previously indicated for the formation dioxetanes and 1,4-endoperoxides, the selectivity decreases considerably in presence of hydroxylic solvents [123]. When hydrogen bonding is no more pos ble in 203, the stereofacial differentiation is steered by steric and electronic rep sion effects at the level of the possible diastereoisomeric transition states 204 is formed selectively (Scheme 54). 

In this chapter, we attempt to review the current state of the art in the applications of cinchona alkaloids and their derivatives as chiral organocatalysts in these research fields. In the first section, the results obtained using the cinchona-catalyzed desymmetrization of different types of weso-compounds, such as weso-cyclic anhydrides, meso-diols, meso-endoperoxides, weso-phospholene derivatives, and prochiral ketones, as depicted in Scheme 11.1, are reviewed. Then, the cinchona-catalyzed (dynamic) kinetic resolution of racemic anhydrides, azlactones and sulfinyl chlorides affording enantioenriched a-hydroxy esters, and N-protected a-amino esters and sulftnates, respectively, is discussed (Schemes 11.2 and 11.3). 

The enantiomerically enriched 4-hydroxyenones 32 are an important class of chiral building blocks. This class of molecules has generally been obtained by the enzymatic or nonenzymatic catalytic desymmetrization of meso-cyclic diols 31 (or their derivatives) that can be prepared from the meso-endoperoxides 30 [32]. It is also well known that achiral bases such as NEt3 can promote the Kornblum-DeLaMare rearrangement of the meso-endoperoxides 30 [33]. This process is believed to proceed via the E2... 

The endoperoxide (293) on catalysis with trimethylsilyl trifluoromethanesulfonate combines with chiral ketones in a highly diastereoselective manner. The behavior of (— )-menthone (295) provides an apt illustration (Equation (43)) <91TL7243>. Only two of the four possible trioxanes are formed in a yield of 21%, the cw-fused 35,55,65 and 3R,5R,6R isomers, (296) and (297), in a 1 1 ratio. Other chiral ketones, such as (-l-)-nopinone and ( —)-carvone react with (293) analogously. 

The enantioselective Kornblum-DeLaMare rearrangement based on the desymmetriza-tion of meio-endoperoxides by a chiral base catalyst has recently been developed. ... 

The prostaglandin endoperoxides PGG2 and PGH2 are metabolized in human platelets to a group of biologically active compounds called the thromboxanes which appear to play an important role in platelet aggregation. One of these compounds, thromboxane B2, has been the subject of much research and a successful synthesis has been achieved.A chiral synthesis of an important... 

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