Silyl hydroperoxides preparation

Silicon and germanium peroxides TABLE 1. Preparation of silyl hydroperoxides 1... 

SCHEME 12. Synthesis of hydroperoxides from silyl enol ethers TABLE 3. Preparation of alkyl hydroperoxides via singlet oxygen oxygenation... 

Silyl alkyl and silyl aryl peroxides 7 are prepared by reaction of alkyl, aryl or aralkyl hydroperoxides with halosilanes (equation 12). Such reactions are carried out in an inert solvent in the presence of an acid acceptor, such as pyridine, ammonia or a tertiary amine in ether or petroleum ether (Table 3) . ... 

Alkyl hydroperoxides can form 2 1 adducts with DABCO. Both nitrogens of DABCO are involved and the resulting adduct contains 2 mol of hydroperoxide per mol of DABCO. Table 4 lists the silyl alkyl peroxides prepared using the DABCO-hydroperoxide adduct techniques. 

Alkyl(chloro)silyl peroxides 8 and alkyl alkoxysilyl peroxides are prepared by the alkyl hydroperoxidation of dichlorodiorganosilane (equations 13-15). 

In the total synthesis of (+)-trienomycins A and F, Smith et al. used an Evans aldol reaction technology to construct a 1,3-diol functional group8 (Scheme 2.1i). Asymmetric aldol reaction of the boron enolate of 14 with methacrolein afforded exclusively the desired xyn-diastereomer (17) in high yield. Silylation, hydrolysis using the lithium hydroperoxide protocol, preparation of Weinreb amide mediated by carbonyldiimidazole (CDI), and DIBAL-H reduction cleanly gave the aldehyde 18. Allylboration via the Brown protocol9 (see Chapter 3) then yielded a 12.5 1 mixture of diastereomers, which was purified to provide the alcohol desired (19) in 88% yield. Desilylation and acetonide formation furnished the diene 20, which contained a C9-C14 subunit of the TBS ether of (+)-trienomycinol. 

The procedure, based on the phosphoramidite method, is illustrated in Scheme 7.11. Nn-Fmoc-L-tyrosine was temporarily protected as its ferf-butyldimethylsilyl ester (see section 6.6). Phosphitylation with dimethyl tyN-diethylphosphorami-dite followed by in situ oxidation with /erf-butyl hydroperoxide gave the phos-phodiester 11 3 The labile silyl ester hydrolysed during the sodium metabisulfite workup used to destroy excess /erf-butyl hydroperoxide to give 11.4 in 57% overall yield, By the same procedure, the dkerf-butyl phosphate 11.5, dibenzyl phosphate 11.6 and diallyl phosphate (not shown) were prepared. 

Sensitized photooxidation of silyl enolates with singlet oxygen followed by reduction of the hydroperoxides with PPhs in methanol has been used for the preparation of chiral and achiral ketones such as (/f)-6-methyl-2-cyclohexen-l-one starting from R)-2-methy Icy clohexanone. ... 

Low-temperature autoxidation of 3,4-dihydro-2//-pyrazoles (e.g. 10, R = Me) provides unstable a-azo hydroperoxides (Scheme 30) [61a,bj 3,4-dihydro-2//-pyrazoles that are inert towards autoxidation (cf. 10, R = Ph) can be converted to hydroperoxides by reaction with singlet oxygen (photooxygenation) at 0- 5 °C [61b], a-Azo hydroperoxides readily decompose at room temperature to -keto radicals which can be entrapped with oxygen to furnish 3-hydroxy-1,2-dioxolanes (e.g. 11 —> 12, Scheme 30) [61cj. The preparation and thermal decomposition of several ether, silyl ether and ester derivatives of 3-hydroxy-1,2-dioxolanes have been reported [62]. 

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