Trimethylsilyl dienol ethers

Another Japanese group developed the Baccatin III synthesis shown in Scheme 13.58. The eight-membered B-ring was closed early in the synthesis using a Lewis acid-induced Mukaiyama reaction (Step B-l), in which a trimethylsilyl dienol ether served as the nucleophile. 

TABLE 2. Regioselective preparation of trimethylsilyl dienol ethers... 

Trimethylsilyl dienol ethers. Reaction ot cyclic enones with 1 equiv. of this activated Fe(0) and ClSi(CH,),/N(C2H,)i results in predominant formation of the exocyclic through-conjugated dienol ether, rather than the. ross-conjugated (kinetic) isomer, which is formed preferentially by deprotonation with I DA. 

Electrophilic Trifluoromethylation with Umemoto s Reagents A.8.1 Trifluoromethylation of the Trimethylsilyl Dienol Ether 30... 

The reaction of trimethylsilyl dienol ethers with PdCl2(NCMe)2 affords palladium 7 -allyls with an aldehyde functionality (Equation (38)). The actual mechanism of the reaction was not discussed but the rearrangement of a palladium enolate transferred from the siloxane moiety seems plausible. A related rearrangement has been observed in a Pd aryloxide that leads to a bis 77 -allylic Pd complex, as was discussed in Section 8.06.3. - ... 

The authors assumed that the catalytically active species might be a copper(I) complex originating from reduction by the silyl dienolate 214. As a consequence, the aldol reaction was performed with the chiral copper(I) complex [Cu(OfBu)-(S)-270], and identical results in terms of the stereochemical outcome were obtained. In addition, the reaction was followed by react IR. The study led to evidence of a copper(I) enolate as the active nucleophile, and the catalytic cycle also shown in Scheme 5.77 was proposed. The reaction of the copper(I) complex Cu(OiBu)-(S)-270 with silyl dienolate 214 represents the entry into the catalytic cycle. Under release of trimethylsilyl triflate, the copper enolate 272 forms, whose existence is indicated by in situ IR spectroscopy. Its exact structure remains unclear, but the description as O-bound tautomer is plausible. Upon reaction with the aldehyde, the copper aldolate 273 is generated, which is then silylated by means of the silyl dienol ether 214 to give the (isolable) silylated alcohol 274 from which the aldol product 271 is liberated during the acidic workup [132b]. 

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