Thioester, olefination

Methyl 4-[2-(ethylthiocarbonyl)ethenyl]cinnamate (3 SMe) crystallizes into a typical a-translation-type packing structure in which the distances between the ethylenic double bonds are 3.988 A and 4.067 A, respectively. However, the 3 SMe crystal is entirely photostable even though it should be photoreactive based on the topochemical rule (Sukegawa, 1991). Several examples of exceptionally photostable diolefin crystals have been found in compounds having a thioester moiety. Such anomalous behaviour of crystals such as 2 OMe and 3 SMe cannot be explained simply in terms of the topochemical rule since this rule involves only the positional relationship between the reactive olefin pair. 

CPv. / Ti Al Tebbe reagent methylenation of aldehydes, ketones, esters, thioesters, amides, carbonates can also induce olefin metathesis in situ preparation [711-713]... 

Sex pheromones in the Lepidoptera are multi-component mixtures consisting mostly of olefinic compounds possessing a terminal aldehyde, alcohol, or acetate moiety. Besides functional group differences, the constituents of lepidopteran sex pheromones vary in hydrocarbon chain length and in the specific number, location, and geometry of double bonds. These chemical structures are formed in biosynthetic pathways involving a limited number of enzymatic steps believed to use fatty-acyl thioesters of coenzyme A (acyl-CoA) as substrates. Key reactions are desaturation, limited [3-oxidation, and a small number of terminal functional group modifications (reviewed in Chapter 3). 

Polyketide and fatty acid biosyntheses begin with condensation of the coenzyme A thioester of a short-chain carboxylic acid starter unit such as acetate or propionate with the coenzyme A thioester of a dicarboxylic acid extender unit such as malonate or methyl malonate. The driving force for the condensation is provided by the decarboxylation of the extender unit. In the case of fetty acid synthesis, the resulting -carbonyl is completely reduced to a methylene however, during the synthesis of complex poly-ketides, the -carbonyl may be left untouched or variably reduced to alcohol, olefinic, or methylene functionalities depending on the position that the extender unit will occupy in the final product. This cycle is repeated, and the number of elongation cycles is a characteristic of the enzyme catalyst. In polyketide biosynthesis, the full-length polyketide chain cyclizes in a specific manner, and is tailored by the action of additional enzymes in the pathway. 

Optically active 1,2-diol units are often observed in nature as carbohydrates, macrolides or polyethers, etc. Several excellent asymmetric dihydroxylation reactions of olefins using osmium tetroxide with chiral ligands have been developed to give the optically active 1,2-diol units with high enantioselectivities. However, there still remain some problems, for example, preparation of the optically active anti-1,2-diols and so on. The asymmetric aldol reaction of an enol silyl ether derived from a-benzyloxy thioester with aldehydes was developed in order to introduce two hydroxyl groups simultaneously with stereoselective carbon-carbon bond formation by using the chiral tin(II) Lewis acid. For example, various optically active anti-a,p-dihydroxy thioester derivatives are obtained in good yields with excellent diastereo-... 

These tellurium-containing polymers were checked for their catalytic activity in the ep-oxidation of olefins and as oxidizing agents. The polymeric 4-methoxyphenyl tellurium oxide did not react with amines, amides, alcohols, or phenols, but oxidized hydroquin-ones to quinones, thiols to disulfides, thioketones to ketones, thioesters to esters, and thiobenzamides in organic solvents to cyanobenzenes and in acetic acid to 2,5-diaryl-4,l, 3-thiadiazoles. ... 

Intermediate 113 was transformed into the trimethylsilyl methyl ketone 119 in quantitative yield via the acid chloride, followed by the addition of trimethylsilylmethyl lithium (Scheme 2.13). Subsequent Peterson olefination of aldehyde 108 with 119 resulted in the required unsaturated ketone 120 in 95% yield. Subsequent desilylation and thioester hydrolysis afforded a 97% of the seco acid 121. Lactonization was achieved in 32% yield via the phosphoric acid-mixed anhydride, however this procedure also formed about 25% of the dimeric bis lactone. Following removal of the acetonide under the action of acid, a nonselective oxidation with RuCl2(Ph3P)3 produced a 1 1 mixture of the natural... 

The two segments were then connected via a Peterson olefination involving the lithium anion of 344 and aldehyde 332 to give the required ( , )-dienone. Thioester cleavage followed by desilylation gave seco acid 345 in 50% overall... 

Vinyl chloride,29 vinyl acetate,30 oc-nitro olefins,31 and azlactones32 also add alkanethiols. The reaction of azlactones is accompanied by ring fission to yield V-acyl / -alkylthio oc-amino thioesters, this being a good preparative route to such compounds ... 

The combination of lactic acid and tartaric acid has been used in the synthesis of (+ )-polyoxamic acid (435), the unusual amino acid component of polyoxin B (Scheme 60). The lactic acid component, ylide 429, is available from 427 by hydrolysis, conversion to thioester 428, and reaction with excess methylenetriphenylphosphorane. Wittig olefination with L-tartrate-derived aldehyde 430 gives the (E)-enone 431. Reduction to syn-alcohol followed by treatment with trifluoroacetonitrile affords 432. 

Reacting thiobenzoic acids with olefins in the presence of a clay catalyst (Montmorillonite K 10) gives the Markovnikov product 17 regioselectively (Scheme 10) [37]. In the absence of a clay catalyst, the addition proceeds in an anti-Markovnikov manner to afford the thioester 18. 

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