Mesylates elimination

This finding is also in agreement with another three-component Michael/aldol addition reaction reported by Shibasaki and coworkers [14]. Here, as a catalyst the chiral AlLibis[(S)-binaphthoxide] complex (ALB) (2-37) was used. Such hetero-bimetallic compounds show both Bronsted basicity and Lewis acidity, and can catalyze aldol [15] and Michael/aldol [14, 16] processes. Reaction of cyclopentenone 2-29b, aldehyde 2-35, and dibenzyl methylmalonate (2-36) at r.t. in the presence of 5 mol% of 2-37 led to 3-hydroxy ketones 2-38 as a mixture of diastereomers in 84% yield. Transformation of 2-38 by a mesylation/elimination sequence afforded 2-39 with 92 % ee recrystallization gave enantiopure 2-39, which was used in the synthesis of ll-deoxy-PGFla (2-40) (Scheme 2.8). The transition states 2-41 and 2-42 illustrate the stereochemical result (Scheme 2.9). The coordination of the enone to the aluminum not only results in its activation, but also fixes its position for the Michael addition, as demonstrated in TS-2-41. It is of importance that the following aldol reaction of 2-42 is faster than a protonation of the enolate moiety. 

The CD fragment 1s synthesized starting with resolved bicyclic acid 129. Sequential catalytic hydrogenation and reduction with sodium borohydride leads to the reduced hydroxy acid 1. The carboxylic acid function is then converted to the methyl ketone by treatment with methyl-lithium and the alcohol is converted to the mesylate. Elimination of the latter group with base leads to the conjugated olefin 133. Catalytic reduction followed by equilibration of the ketone in base leads to the saturated methyl ketone 134. Treatment of that intermediate with peracid leads to scission of the ketone by Bayer Villiger reaction to afford acetate 135. The t-butyl protecting... 

Mercuric acetate, 289, 328 Mercuric oxide, 402 Mesylates, elimination, 107 —, nucleophilic substitution, 42-... 

A mesylate elimination was also used to prepare sulfone 11, l-methyl-4-[(methylenecycloprop-yl)sulfonyl]benzene, using potassium tert-butoxide in tert-butyl alcohol as the base. The methylenecyclopropane was contaminated with a small amount of the corresponding sulfonyl-bicyclobutane 12. 

A double mesylate elimination using potassium /ert-butoxide in tetrahydrofuran was attempted as a means of preparing 7,7-dichloro-2,3-bis(methylene)bicyclo[4.1.0]heptane (14, X = Cl) and its 7,7-dibromo analog from the corresponding diols. However, only low yields of the dienes... 

The enone 3 was further functionalized via tandem reaction by Michael addition of methanol to the conjugate system at C-5, followed by base catalyzed nitromethane addition to the keto function at C-2 and base catalyzed (TMG -tetramethylguanidine) mesylation/elimination with the formation of new a-nitroenone as depicted in Scheme 7. The intermediate a-nitroenone functionalized at C-2 as a conjugate system is indeed an excellent Michael acceptor of reactive nucleophiles, including 1-thio-P-D-glucose. The conjugate addition of this reactive thiol was performed in the same fashion as before (2, 3) with the stereoselective formation of the first representative example of highly functionalized and previously unknown class of C-nitro-5-thiodisaccharide derivatives. 

Stereochemical control was achieved by enzymatic desymmetrization of propanediol 118, whereas the tetronic core was introduced via an aldol condensa-tion/mesylation/elimination sequence. 

Recently, a Peterson-type olefination variant of this strategy was explored by Parrain and coworkers [203]. By incorporating a trimethylsUyl group in the pentadienyl anion equivalent 246, alcohols 248 that readily undergo Lewis-acid-catalyzed y-elimination were formed as addition products of aldehydes 247 (Scheme 1.42). The one-step, facile elimination is an improvement on the mesylation/elimination approach of Fallis. Interestingly, while alcohols of the type 248 and 251 bearing different, substituted alkenyl substituents have been... 

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