Condensations Mukaiyama redox condensation

Scheme 8 summarizes the introduction of the missing carbon atoms and the diastereoselective epoxidation of the C /C double bond using a Sharpless asymmetric epoxidation (SAE) of the allylic alcohol 64. The primary alcohol 62 was converted into the aldehyde 63 which served as the starting material for a Horner-Wadsworth-Emmons (HWE) reaction to afford an E-configured tri-substituted double bond. The next steps introduced the sulfone moiety via a Mukaiyama redox condensation and a subsequent sulfide to sulfone oxidation. The sequence toward the allylic alcohol 64 was com-... 

The sulfonyl hydrazide D is obtained through a Mukaiyama redox condensation while consuming compounds A-C (cf. Figure 2.38). 

In six more steps alkyne 22 is transformed into sulfone 24 (building block III) for the final coupling reaction. These steps include TBS deprotection (75 %, over 2 steps from 20), palladium-catalyzed addition to methoxy tetrolate (61 %), DIBAL reduction (91 %), Mukaiyama redox condensation (86 %), acetylation (97 %) and (NH4)6Mo7024-catalyzed oxidation with H2O2 (99 %). 

Starting from (+)-diethyl tartrate (2), bromobutenolide 18 was obtained in nine steps. Three of the four C=C double bonds were built up using a Wittig reaction (11—>12), an Ando- y Q Horner-Wadsworth-Emmons reaction (13— 15) and (3-elimination (16 18). From (-)-actinol (3) stannane 23 and sulfone 24 were synthesized in 9 and 13 steps, respectively. Their common intermediate, alkyne 22, was synthesized using methoxycarbonylation. Sharpless asymmetric epoxidation and Ci-elongation with lithio trimethylsilyldiazomethane. Stannane 23 was obtained upon hydrostannylation and TBS deprotection. Sulfone 24 was obtained after addition to methyl tetrolate, reduction, Mukaiyama redox condensation, acetylation and catalytic oxidation. 

Fig. 2.36. Preparatively important redox condensations according to Mukaiyama, and related reactions.

Another efficient method seems to be Mukaiyama s redox condensation, which has found widespread application in total syntheses of natural products. Originally 5-(2-pyridyl)carbothioates (18), obtained from carboxylic acids, 2,2 -dipyridyl disulfide and triphenylphosphine (equation 8), were used in follow-up reactions. The use of (18) has been reviewed in the literature. - ... 

Mukaiyama reaction, a redox condensation approach to peptide synthesis. A disulfide (2,2 -dipyridyldisulfide) reduction combined with a phosphine (triphenylphos-phine) oxidation provides the driving force for the condensation of the carboxy component with the amino component [T. Mukaiyama et al., in The Peptides Analysis, Synthesis, Biolc, Volume 2, E. Gross,... 

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