Aldehydes oxidation reactions, silyl enol ether derivatives

Given this problem, the attachment of the butanone synthon to aldehyde 74 prior to the methyl ketone aldol reaction was then addressed. To ovenide the unexpected. vTface preference of aldehyde 74, a chiral reagent was required and an asymmetric. syn crotylboration followed by Wacker oxidation proved effective for generating methyl ketone 87. Based on the previous results, it was considered unlikely that a boron enolate would now add selectively to aldehyde 73. However, a Mukaiyama aldol reaction should favour the desired isomer based on induction from the aldehyde partner. In practice, reaction of the silyl enol ether derived from 87 with aldehyde 73, in the presence of BF3-OEt2, afforded the required Felkin adduct 88 with >97%ds (Scheme 9-29). This provides an excellent example of a stereoselective Mukaiyama aldol reaction uniting a complex ketone and aldehyde, and this key step then enabled the successful first synthesis of swinholide A. 

Six-membered chiral acetals, derived from aliphatic aldehydes, undergo aldol-type coupling reactions with a-silyl ketones, silyl enol ethers," and with silyl ketene acetals " in the presence of titanium tetrachloride with high diastereoselectivities (equation 41) significant results are reported in Table 20. This procedure, in combination with oxidative destructive elimination of the chiral auxiliary, has been applied... 

Dihydropyran derivatives can be synthesized facilely by a smooth oxidative Mukaiyama-Michael addition followed by a cyclization with silyl enol ethers in the presence of Dess Martin periodinane (DMP) and pyridine under mild reaction conditions from MBH adducts in a one-pot process (Scheme 4.95). Notably, these dihydropyrans were obtained exclusively as cw-isomers in good yields. Moreover, all the reactions worked very well, irrespective of whether MBH adducts were derived from aliphatic or aromatic aldehydes, and silyl enol ethers were derived from acetophenone, cyclohexanone or cyclopentanone. 

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