- Highly diastereoselective synthesis of 2-(1-N-Boc-aminoalkyl)thiazole-5-carboxylates by reduction of tert-butylsulfinyl ketimines
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Positional isomers of naturally occurring peptide subunits were synthesized via highly diastereoselective reduction of tert-butylsulfinyl ketimines as a key reaction. While NaBH4 reduction of ketimines derived from 2-thiazolyl ketones afforded the (RS,R)-isomer with moderate diastereoselectivity, L-Selectride reduction afforded the (RS,S)-isomer as the sole product. In contrast, ketimines derived from tert-butyl 2-thiazolyl ketone afforded the (RS,R)-isomer with low diastereoselectivity by both NaBH4 and L-Selectride reduction. Stereochemistry of the reaction was discussed based on calculation of the conformational energies for ketimines.
- Magata, Takuji,Hirokawa, Yoshimi,Furokawa, Aya,Takeuchi, Kazuhisa,Ohtomo, Yoshiaki,Kino, Toshitaka,Kominami, Jun,Nakai, Yuto,Kitamura, Maria,Maezaki, Naoyoshi
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p. 416 - 422
(2018/04/09)
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- Synthesis of (Trimethylsilyl)thiazoles and Reactions with Carbonyl Compounds. Selectivity Aspects and Synthetic Utility
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Synthetic routes to all possible regioisomeric mono- and bis(trimethylsilyl)thiazoles as well as to the tris(trimethylsilyl) derivative via lithiation-silylation sequences of the thiazole ring followed by selective protodesilylation in some cases are described. (Trimethylsilyl)thiazoles serve as thiazolyl donor synthons upon reaction with carbonyl compounds (ketenes, acyl chlorides, aldehydes) for the preparation of mono- and bis-substituted thiazoles in very good yields.Carbodesilylation occurs more readily at the 2- than 5-position, whereas no reaction takes place at the 4-position.A mechanism via a thiazolium 2-ylide as an intermediate is suggested for the carbodesilylation at the 2-position.
- Dondoni, Alessandro,Fantin, Giancarlo,Fogagnolo, Marco,Medici, Alessandro,Pedrini, Paola
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p. 1748 - 1761
(2007/10/02)
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- NEW PERSPECTIVES IN THIAZOLE CHEMISTRY
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Carbon-carbon bond forming reactions at C-2 of the thiazole ring have been carried using two strategies, one involving the addition of organometallic reagents (lithium carbanions of esters, Grignard salts, silyl enol ethers, silyl ketene acetals, silylazoles) to N-acylthiazolium salts; the other involving the addition of carbon electrophiles (ketenes, acyl chlorides, anhydrides, aldehydes) to N-acylthiazolium ylides generated in situ.The reactions have been applied to 1,3-thiazole and 2-trimethylsilyl-1,3-thiazole, the latter being more reactive than the former toward electrophiles.This methodology constitutes a new entry to a variety of functionalized thiazoles and thiazolines which are potential building blocks for the synthesis of natural compounds and analogues of biologically active molecules (penems, arylpropionic acids).Some ring transformations of thiazoles induced by carbon-sulfur bond cleavage are also described.The fundamental role played by the sulfur atom of the thiazole ring in the observed reactions is pointed out and briefly discussed.
- Dondoni, Alessandro
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- REACTIONS OF 2-TRIMETHYLSILYLYHIAZOLE WITH ACYL CHLORIDES AND ALDEHYDES SYNTHESIS OF NEW THIAZOL-2-YL DERIVATES
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2-Trimethylsilylthiazole (1) undergoes ipso-substitution of the silyl group with various acyl chlorides and ethyl chloroformate affording 2-acylthiazoles (2)-(5) but adds by the carbon-silicon bond to the carbonyl group of aldehydes yielding thiazol-2-yl-trimethylsiloxy-methane derivates (7).
- Medici, Alessandro,Fantin, Giancarlo,Fogagnolo, Marco,Dondini, Alessandro
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p. 2901 - 2904
(2007/10/02)
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