Reductive Esterification

Dioxepanes 63 were hydrolyzed with aqueous hydrochloric acid to the starting diol. A thionyl chloride promoted ring-opening of dioxepane 63 to intermediate 64 has been reported. When treated with base, compound 64 can be transformed into vinylic ether 65 in 58% yield (81ZOR1047) (Scheme 31). 3-Methylfurazan-4-acetic acid was converted to the vinyl derivative 66 via an esterification, reduction, mesylation, and base elimination sequence (81JHC1247) (Scheme 31). 

The classic method for controlling stereochemistry is to perform reactions on cyclic substrates. A rather lengthy but nonetheless efficient example in the prostaglandin field uses bicyclic structures for this purpose. Bisacetic acid derivative S is available in five steps from Diels-Alder reaction of trans-piperylene and maleic anhydride followed by side-chain homologation. Bromolactonization locks the molecule as bicyclic intermediate Esterification, reductive dehalogen-... 

Metallation of 3,4-dimethyl-l,2,5-thiadiazole (55) to the anion (56) was accomplished with the use of a nonnucleophilic base, lithium diisopropylamide <82JHC1247>. Nucleophilic attack at sulfur resulted in an alkyllithium reagent <70CJC2006>. The lithiomethyl derivative (56) was carboxylated to (57) with carbon dioxide and converted to the vinyl derivative (58) via an esterification, reduction, mesylation, and base elimination sequence (Scheme 12). 

Synthesis of aldohexoses from 422 (n = 2) telomers was achieved by way of cyanide intermediate s. On treatment with potassium cyanide, each of the dichloromethyl compounds 449 and 451 gave28 5 a pair of epimeric nitriles (463-466) that were converted, in moderate yield, into DL-galactose, DL-altrose, DL-idose, and DL-glucose by conventional procedures involving esterification, reduction, and final hydrolysis of the dichloromethyl group. 

The distribution of metabolites obtained after incubation of pineapple slices with keto acids and keto esters, potential precursors of the corresponding hydroxy compounds, is summarized in Table II. The metabolization steps comprise esterification, reduction to hydroxy compounds, formation of acetoxy esters, and cyclization to the corresponding lactones. Metabolization rate and distribution of formed products strongly depend on the structures of the precursors. The detection of these metabolites proves the enzymatic capability of pineapple tissue to catalyze these conversions, an aspect which might be interesting for future use of pineapple tissue cultures in the production of chiral compounds. 

Barton Esterification Reductive Decarboxylation. O-Acyl thiohydroxamates or Barton esters are useful precursors of carbon-centered radicals via thermolysis or photolysis. Several different methods are available for converting carboxylic acids into Barton esters (eq 1). These reactions generally proceed via the attack of a 2-mercaptopyridine-N-oxide salt on an activated carboxylic acid that has either been preformed (acid chloride, mixed anhydride) or generated in situ (with 1,3-dicyclohexylcarbodiimide or tri-n-butylphosphine + 2,2 -dithiodipyridine-l,r-dioxide). However, HOTT has the distinct advantages of (1) being easy to prepare and handle without the need for any special precautions, (2) facilitates efficient Barton esterification of carboxylic acids, and (3) simplifies subsequent work-up and purifications by avoiding the need to remove by-products like 1,3-dicyclohexylurea. 

Enzymes can be utilized to affect a number of transformations the broad spectrum of reactions, including amide bond formation, hydrolysis, esterification, reduction, oxidation, and carbon-carbon bond formation, has been reviewed elsewhere (114). 

The order of events in the synthesis is chosen to minimise unwanted reactions the free amino group in (23) might interfere with the esterification reduction is kept to the end. 

Therefore, it is always advisible to employ the previously cited reaction sequence rigidly viz., oxidation-esterification-reduction, in order to circumvent these aforesaid difficulties. Further, the commercial production of benzocaine is usually carried out by catalytic hydrogenation in place of using zinc dust. 

The introduction of mono-, di-, and oligosaccharide units on dendritic surfaces is usually carried out as the final synthetic step in monodendron and dendrimer synthesis. For this purpose, well-known polymer analogous/ organic conversion steps are used amidation, esterification, reductive amina-tion, nucleophilic substitution, addition/elimination, thiol-ene reaction, 1,3-dipolar cycloaddition, and others (Fig. 5.22). 

The unique reactivity of eleostearic acid enhances its participation in a variety of chemical reactions, such as carbon-carbon double bond addition, acid-base reactions, esterifications, reduction reactions, Diels-Alder reactions, and thermal polymerization. Recent descriptive examples of a few of these reactions, and how they can be applied to the production of various useful products, are listed in the following section. 

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