Dioxygenation, stereoselective

Dioxolane synthesis, 192-273 fused bicyclic dioxolanes, 193, 194 Dioxygenation, stereoselective, 339-48 Dioxymethane, molecular orbital treatment, 28-9... 

Dioxygenation of the chiral enoate 34 could also be conducted stereoselectively, although the selectivity was rather low (dr 4.5 1, Scheme 22). In compound 34 the naphthylmenthol auxiliary effectively blocked one face of the tethered enoate so that the oxygen can only be transferred from the non-blocked face. The observed... 

In a search for more effective approaches to the problem of stereoselective dioxygenation, alternative methods have been developed. While the inclusion of alkenes and O2 within a chiral cyclodextrin cavity furnished hydroperoxides with modest ee values, neighboring stereocenters and chiral auxiliaries could induce highly stereoselective dioxygenation. In 1987 Kropf and Reichwaldt, and three years later Adam and coworkers reported on the photooxygenation of phenyl-substituted alkenes 36 producing allyUc hydroperoxides 37 and 38 with high diastereoselectivity (dr 80/20). In the best example... 

There are also several situations where the metal can act as both a homolytic and heterolytic catalyst. For example, vanadium complexes catalyze the epoxidation of allylic alcohols by alkyl hydroperoxides stereoselectively,57 and they involve vanadium(V) alkyl peroxides as reactive intermediates. However, vanadium(V)-alkyl peroxide complexes such as (dipic)VO(OOR)L, having no available coordination site for the complexation of alkenes to occur, react homolyti-cally.46 On the other hand, Group VIII dioxygen complexes generally oxidize alkenes homolytically under forced conditions, while some rhodium-dioxygen complexes oxidize terminal alkenes to methyl ketones at room temperature. 

The oxidation of iV-methoxycarbonyl-l,2-dihydropyridine 56 with K 2-chloroperbenzoic acid results in /ra j-dioxygenation of the 5,6-alkene to give the allylic alcohol 57<1998JOC10001> (Scheme 16). The reaction is thought to proceed via an unstable aminoepoxide which is regio- and stereoselectively trapped by m-chloiobenzoic acid. 

The aldol reaction is the preferred method for the stereoselective synthesis of 1,3-dioxygenated building blocks. In 1978, Enders et al. reported the first enantioselective aldol reaction in the difficult case of a-unsubstituted (3-ketols using SAMP and RAMP. Diastereo- and enantiomerically pure yyn-(3-ketols are available by aldol reaction of SAMP/RAMP... 

The insertion of an oxygen atom(s) into a molecule in a regioselective/ stereoselective manner can be catalyzed by a broad group of enzymes. The target molecules are diverse in nature as illustrated by the following examples. The source of oxygen can be dioxygen or water. 

The development of new well-defined and robust compounds suitable for efficient applications in dioxygen transport or carbon monoxide detoxification and in catalytic regioselective and stereoselective oxidations of various compounds will be the major challenge in the near future. 

Dussault and Woller have also reported on the enantioselective photooxygenation of allylic alcohols (e.g., 112) with the aim of synthesizing 1,4-dioxygen-ated peroxides (113) [154]. The photooxygenation illustrated in Scheme 26 gave 113 in 58% yield, with good stereoselectivity. 

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