Boron and Silicon Lewis Acids for Mukaiyama Aldol Reactions

2008 ◽  
pp. 25-68 ◽  
Author(s):  
Kazuaki Ishihara ◽  
Hisashi Yamamoto
Keyword(s):  
Lewis Acids ◽  
Aldol Reactions ◽  
Mukaiyama Aldol

Boron and Silicon Lewis Acids for Mukaiyama Aldol Reactions

ChemInform ◽  
2005 ◽  
Vol 36 (30) ◽  
Author(s):  
Kazuaki Ishihara ◽  
Hisashi Yamamoto
Keyword(s):  
Lewis Acids ◽  
Aldol Reactions ◽  
Mukaiyama Aldol

scholarly journals Divergent Asymmetric Total Synthesis of All Four Pestalotin Diastereomers from (R)-Glycidol

Molecules ◽  
2020 ◽  
Vol 25 (2) ◽  
pp. 394 ◽  
Author(s):  
Mizuki Moriyama ◽  
Kohei Nakata ◽  
Tetsuya Fujiwara ◽  
Yoo Tanabe
Keyword(s):  
Total Synthesis ◽  
Lewis Acids ◽  
Alder Reaction ◽  
Diels Alder ◽  
Aldol Reactions ◽  
Asymmetric Total Synthesis ◽  
High Chemical ◽  
Diels Alder Reaction ◽  
Mukaiyama Aldol ◽  
Optical Rotations

All four chiral pestalotin diastereomers were synthesized in a straightforward and divergent manner from common (R)-glycidol. Catalytic asymmetric Mukaiyama aldol reactions of readily-available bis(TMSO)diene (Chan’s diene) with (S)-2-benzyloxyhexanal derived from (R)-glycidol produced a syn-aldol adduct with high diastereoselectivity and enantioselectivity using a Ti(iOPr)4/(S)-BINOL/LiCl catalyst. Diastereoselective Mukaiyama aldol reactions mediated by catalytic achiral Lewis acids directly produced not only a (1′S,6S)-pyrone precursor via the syn-aldol adduct using TiCl4, but also (1′S,6R)-pyrone precursor via the antialdol adduct using ZrCl4, in a stereocomplementary manner. A Hetero-Diels-Alder reaction of similarly available mono(TMSO)diene (Brassard’s diene) with (S)-2-benzyloxyhexanal produced the (1′S,6S)-pyrone precursor promoted by Eu(fod)3 and the (1′S,6R)-pyrone precursor Et2AlCl. Debenzylation of the (1′S,6S)-precursor and the (1′S,6R)-precursor furnished natural (−)-pestalotin (99% ee, 7 steps) and unnatural (+)-epipestalotin (99% ee, 7 steps), respectively. Mitsunobu inversions of the obtained (−)-pestalotin and (+)-epipestalotin successfully produced the unnatural (+)-pestalotin (99% ee, 9 steps) and (−)-epipestalotin (99% ee, 9 steps), respectively, in a divergent manner. All four of the obtained chiral pestalotin diastereomers possessed high chemical and optical purities (optical rotations, 1H-NMR, 13C-NMR, and HPLC measurements).

scholarly journals Syn-selective silicon Mukaiyama-type aldol reactions of (pentafluoro-λ6-sulfanyl)acetic acid esters with aldehydes

2018 ◽  
Vol 14 ◽  
pp. 373-380 ◽  
Author(s):  
Anna-Lena Dreier ◽  
Andrej V Matsnev ◽  
Joseph S Thrasher ◽  
Günter Haufe
Keyword(s):  
Acetic Acid ◽  
Aldol Condensation ◽  
Aldol Reactions ◽  
Complex Structures ◽  
Bond Forming ◽  
Hydroxyalkanoic Acid ◽  
Mukaiyama Aldol ◽  
Substituted Benzaldehydes ◽  
Acetic Acid Esters ◽  
Acid Esters

Aldol reactions belong to the most frequently used C–C bond forming transformations utilized particularly for the construction of complex structures. The selectivity of these reactions depends on the geometry of the intermediate enolates. Here, we have reacted octyl pentafluoro-λ6-sulfanylacetate with substituted benzaldehydes and acetaldehyde under the conditions of the silicon-mediated Mukaiyama aldol reaction. The transformations proceeded with high diastereoselectivity. In case of benzaldehydes with electron-withdrawing substituents in the para-position, syn-α-SF5-β-hydroxyalkanoic acid esters were produced. The reaction was also successful with meta-substituted benzaldehydes and o-fluorobenzaldehyde. In contrast, p-methyl-, p-methoxy-, and p-ethoxybenzaldehydes led selectively to aldol condensation products with (E)-configured double bonds in 30–40% yields. In preliminary experiments with an SF5-substituted acetic acid morpholide and p-nitrobenzaldehyde, a low amount of an aldol product was formed under similar conditions.

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