Dienes, esterification with

The common nonenolide core of ascidiatrienolide and the didemnilactones has been formed as shown in Scheme 5 (22). Specifically, a tin-mediated, ultrasound-promoted addition of allyl bromide to unprotected glyceraldehyde 37 furnished a mixture of the corresponding homoallyl alcohols 38 which were subjected to acetalization and esterification with 5-hexenoic acid under standard conditions. At that stage, the major jy/i-isomer 40 can be purified by flash chromatography. Exposure of this diene to a refluxing solution of the ruthenium... 

The Diels-Alder cycloaddition reaction of 2,6-dimethyl-1,4-benzoquinone with methyl (ii)-3,5-hexadienoate, carried out in toluene as solvent, gives only traces of the cycloadduct shown in Eq. (5-160), even after seven days. However, when the solvent is changed to water and sodium ( )-3,5-hexadienoate is used as the diene, 77 cmol/mol of the desired cycloadduct is obtained after one hour and esterification with diazomethane [714] f Again, hydrophobic interactions between diene and dienophile in the aqueous medium seem to be responsible for this remarkable and synthetically useful rate acceleration. 

Isomerizations. A convenient method for the conversion of alkynes to conjugated dienes is by treatment with Ph P. The synthetic application is shown in the preparation of 2,4-alkadienols from 2-alkynoic acids involving esterification with pentafluorophenol, isomerization with PhjP (PhMe, 50°), and reduction with DIBAL-H. Even propargyl bromide can be isomerized to give 1-bromopropadiene, albeit in 29% yield. Conjugated alkadienoic esters and amides are obtained in one step from the pentafluorophenyl alkynoates on reaction with alcohols and amines, respectively, after treatment with catalytic amount of PhjP. 

Removal of the unreacted diene, bp 45 °C/20 torr, followed by distillation, bp 123 °C/0.2 torr, gave /-menthyl chrysanthemate (4.7 g, 76%) whose GC analysis showed the following composition d-trans, 89.9% l-trans, 2.7%, and the cis isomers, 7.4%. The cis/trans ratio was 7/93 and ee of the trans isomer was 94%. Complete hydrolysis of the /-menthyl ester with potassium hydroxide in aqueous ethanol followed by esterification with d-2-octanol in the presence of thionyl chloride and pyridine gave the corresponding d-2-octyl ester. GC analysis revealed the following composition d-trans, 90.4% l-trans, 4.7% d-cis, 3.6%, and... 

Two other related compounds were isolated from a different colony of the same species growing in a separate district. Endiandric acid B, ( )-4-(6 -phenyl-tetracyclo-[5,4,2,0 ]trideca-4, 6 -dien-l r-yl)but-2-enoic acid (116), was purified from the small amount of co-existing endiandric acid A (115) by esterification with diazomethane, separation, and subsequent hydrolysis (4). Chemical and spectroscopic evidence proved that endiandric acid B was a vinylog of endiandric acid A. The structure of the other compound, abbreviated as acid C, was determined by H-NMR spectroscopy and also by X-ray crystallography on a Diels-Alder adduct with A-methyl-maleimide as 4-[(E, E )-5 -phenylpenta-2, 4 -dien-r-yl]tetracyclo-[5,4,0,0 , 0 ]undec-10-ene-8-carboxylic acid (117) (6). 

The photochemical fragmentation of vinyl-substituted 1,2k5-oxaphosphetanes, representing a step of a photochemical variant of the Wittig reaction with methyl-eneoxophosphoranes, has been examined as a model in the case of 22b20). Photolysis of this compound in methanol affords the 1,3-diene 24b as well as the highly reactive dioxophosphorane 23 which is trapped by the solvent subsequent esterification of the half-ester 62, formed as a primary product, with diazomethane to give the diester 63 was undertaken solely for preparative reasons 20). 

BASIC PROTOCOL I PREPARATION OF FATTY ACID METHYL ESTERS FROM LIPID SAMPLES CATALYZED WITH BORON TRIFLUORIDE IN METHANOL In this method, lipid samples are first saponified with an excess of NaOH in methanol. Liberated fatty acids are then methylated in the presence of BF3 in methanol. The resulting fatty acid methyl esters (FAMEs) are extracted with an organic solvent (isooctane or hexane), and then sealed in GC sample vials for analysis. Because of the acidic condition and high temperature (100°C) used in the process, isomerization will occur to those fatty acids containing conjugated dienes, such as in dairy and ruminant meat products, that contain conjugated linoleic acids (CLA). If CLA isomers are of interest in the analysis, Basic Protocol 2 or the Alternate Protocol should be used instead. Based on experience, this method underestimates the amount of the naturally occurring cis-9, trans-11 CLA isomer by -10%. The formulas for the chemical reactions involved in this protocol are outlined in Equation D1.2.1 Saponification RCOO-R + NaOH, RCOO-Na + R -OH v 100°C DC Esterification RCOO-Na + CH,OH r 3 v RCOO-CH, + NaOH ioo°c ... 

The initial strategy to fix both side chains containing the Diels-Alder reactants to a sp center was maintained. Compound 63 was synthesized by alkylation and esterification. The second chain with the diene unit was introduced by a Grignard reaction. Ketalization and transformation of the vinyl bromide with tert-... 

Asymmetric Dieh-Alder Reactions. The commercial availability of either enantiomer of camphorsulfonic acid has made it quite useful in asymmetric Diels-Alder reactions. Reaction of the sultone (generated from CS A) with Lithium Diisopropylamide followed by esterification and (3-elimination yields the crystalline acrylate (eq 14). The Lewis acid-catalyzed [4 + 2] cycloaddition of 1,3-dienes with this acrylate affords the corresponding scalemic adduct which can be reduced with Lithium Aluminum Hydride to yield an enantiomerically pure alcohol (eq 15). ... 

More recently, Danishefsky reported a fully synthetic route to tunicamin-yluracil (274) derived from tunicamycin (85JA7761) and hikosamine (284) (85JA7762). Cyclocondensation of the ribosederived aldehyde (260) (84JOC1955) (Scheme 35) with diene 259 under catalysis by Eu(fod)3 (83JA3716) afforded an 86% yield of the carbon-linked disaccharide 261. Ozonolysis of 261, followed by oxidative treatment and esterification, furnished the /3-hydroxy ester 262 and its benzyloxymethyl ether 263. 

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