Tandem Tamao oxidation

One of the important advantages of the intramolecular alkene silylformylation reaction as an aldol equivalent is that the products are masked 3,5-dihydroxyalkanals, and therefore that no manipulations are required prior to iteration of the process by aldehyde al-lylation to set up the next intramolecular silylformylation. Given that allylsilanes are well-known aldehyde allylation reagents, intramolecular silylformylation employing a diallylhydrosilane would, in principle, allow for the possibility of a tandem silylformyla-tion/allylsilylation reaction. This has been reduced to practice the diaUylsilyl ethers 60 were subjected to the previously developed silylformylation conditions and the unpuri-fied reaction mixtures were subjected to the Tamao oxidation ]36] to provide triols 61... 

Fraser-Reid s stereocontrolled synthesis of the Woodward reserpine precursor 195 relied upon a tandem 5-exol6-exo radical cyclization of pyranose-derived dienes [76-77]. As outlined in Scheme 36, a,P-unsaturated ester 188 was prepared by free radical coupling of iodide 187 with a tin acrylate. After hydrolysis of 188 (MeONa, MeOH, 100%) to give primary alcohol 189, the silicon tethered diene 190 was installed by silylation. Treatment of 190 with n-BujSnH led to the desired cage molecule 192 in high yield via a 5-exo-trig cyclization to intermediate 191 followed by a 6-exo cyclization. Tamao oxidation of tricycle 192 led to diol... 

Malacria and co-workers developed a synthetic route to linear triquinanes by transannular radical cyclizations of the , -cycloundeca-4,8-dien-l-yne 114. Upon radical initiation, the primary radical 115 underwent the 5-exo-dig cycli-zation to give 116 (Scheme 20.31), which in turn participated in tandem transannular radical cyclzations to give a single diasteromeric triquinane 119. This was followed by the Tamao oxidation to give 120 in 60% yield. 

Bis(allyl)homoallyloxysilanes 56a and 56b are designed for a tandem intramolecular silylformylation-allylsUylation reaction, which has turned out to be an efficient approach to construct polyol and polyketide frameworks [21], For example, heating a solution of 56 in benzene at 60 °C in the presence of Rh(acac)(CO)2 under CO atmosphere followed by the Tamao oxidation gives syn,syn-triols 59 stereoselectively via oxasilacyclopentanes 57 and 58 (Scheme 5.14). Bis(ds-cro-tyl)silane 56b is readily prepared by double Pd-catalyzed 1,4-hydrosilylation of 1,3-butadiene with dichlorosilane followed by reduction with UAIH4 and alcoholysis with the corresponding homoallylic alcohol. 

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