Oxidative desilylation

Diisopropylamino(dimethyl)silyl]-2-propenyl]lithium adds to aromatic and x-branched aldehydes in the presence of anhydrous zinc chloride with essentially complete anti stereoselectiv-ity3s. as expected from the chair-like pericyclic transition state formed by the ( -intermediate. The addition products are not isolated, but after O-silylation, oxidative desilylation with retention of configuration forms the rmft-diols. 

The ring-opening of the cyclopropane nitrosourea 233 with silver trifiate followed by stereospecific [4 + 2] cycloaddition yields 234 [129]. (Scheme 93) Oxovanadium(V) compounds, VO(OR)X2, are revealed to be Lewis acids with one-electron oxidation capability. These properties permit versatile oxidative transformations of carbonyl and organosilicon compounds as exemplified by ring-opening oxygenation of cyclic ketones [130], dehydrogenative aroma-tization of 2-eyclohexen-l-ones [131], allylic oxidation of oc,/ -unsaturated carbonyl compounds [132], decarboxylative oxidation of a-amino acids [133], oxidative desilylation of silyl enol ethers [134], allylic silanes, and benzylic silanes [135]. 

The functionalized [4]radialene 86 offers opportunities for further transformations by hydrolytic cleavage of the O-silylenol moieties and by oxidative desilylation (Scheme 16). Base- and acid-catalyzed hydrolyses lead to different products (130 and 131, respectively)60. By analogy with the formation of 1,4-diketones by oxidative coupling of two siloxyalkene molecules, treatment of 86 with the iodonium salt Phl+—O—+I—Ph BF4 in dichloromethane leads to 132 which is immediately... 

Diels-AUer reactions. This diene can serve as a precursor to the highly oxygenated cyclohexane derivative shikimic acid (3), as shown in Scheme 1. Oxidative desilylation of the Diels-Alder adduct 2 could not be effected with peracids, but was effected by cis-dihydroxylation (Upjohn procedure, 7, 256-257) followed by p-elimination of (CH3)3SiOH with TsOH. Introduction of the 4a,5P diol system was effected indirectly from the 4a,5a-epoxide in several steps, since direct hydrolysis of the epoxide resulted in a mixture of three triols.1... 

Entry Starting Material Hydrosilylation Catalyst5 Oxidation/ Desilylation Conditions Major Product d.r. Yield (%)... 

Hydrosilylation. Chiral a-arylethanol can be synthesized from styrenes via hydrotri-chlorosilylation and oxidative desilylation. The first step is accomplished with a Pd catalyst containing ligand 6. ... 

Oxidative desilylation. An allylsilane moiety is rendered electrophilic by Li2PdCl4-CuCl2. Thus, cyclization occurs when the molecule is hydroxylated at a proper position. 

Hydroxymethylation. The organolithium reagent is obtained by lithiation of 2-trimethylsilylpyridine. Its alkylation with RX and oxidative desilylation to provide RCH2OH are quite strightforward. 

Propargylic alcohols can be syntl ifid oxidative desilylation. This reac ne silyl group to a prolinol methyl ei... 

Hetero allylboranesP The 3-amino- and 3-silylallyl derivatives are very valuable reagents for the synthesis of anti-3-amino-l-alken-4-ols and anfi -l-alkene-3,4-diols, respectively, by condensation with aldehydes. In the latter cases, an oxidative desilylation is required. 

Oxidative desilylation. From silanes bearing an electron-withdrawing substituent (e.g., Ph, OR), the method provides access to alcohols with retention of configuration. A double bond in the same molecule is retained. Vinylsilanes furnish ketones. ... 

Enones. Oxidative desilylation of cyclic triisopropylsilyl enol ethers with CAN in DMF leads to enones. - ... 

Substituted allylic alcohoh. The synthesis from esters by a two-step branching homologation process involves nucleophilic attack of an (alkoxysilyl)methylmagnesium chloride (2 equiv.) and oxidative desilylation. 

Table 2. Reduction and oxidation with subsequent oxidative desilylation.

In 2008, Nicolaou andLi reported a synthesis of diversonol (932) (Scheme 13.14) (635). The synthesis involved the nucleophilic addition of a lithiated cyclohexene species derived from bromide 938 with the allyl-protected aldehyde 939, followed by oxidation, desilylation, deallylation, and spontaneous xanthone-ring closure of the intermediate phenol (not shown). As in the Brdse synthesis, the enol moiety is oxidized and the C-ring ketone reduced with NaBH4 to generate diversonol (932), which was obtained in eight steps from cyclohexenone 937. 

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