Tandem silylformylation/allylsilylation

The tandem silylformylation/allylsilylation reaction is particularly well suited to the synthesis of skipped polyol motifs such as are found in the oxopolyene macroHdes. The synthesis of protected triol 43 (an intermediate in the mycoticin A formal synthesis described above see Scheme 5.18) relied on an application of this methodology. Thus, homoallylic alcohol 76 was transformed into triol 77 in 55% overall yield and >10 1 diastereoselectivity (Scheme 5.27) [23]. Selective protection of the triol to give 43... 

The tandem silylformylation-allylsilylation of a diallylsilyl ether has been reported by Leighton, using [Rh(acac)(CO)2] as the catalyst (equation 11). This method was optimized and extended to propargylic systems where good diastere-oselectivity can be achieved using the isopropyl derivative. A mechanism is proposed for the stereoselectivity involving coordination of the silicon by both of the oxygen atoms (equation 12). 

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... 

---