Allyl esters, carboxylic acids

Moreover, in 1998 Ube Industries, Ltd. discovered that PC decomposition is suppressed by small quantities of additives (carboxylic acid vinyl esters, such as vinyl acetate (7) and divinyl adipate (8) vinyl carbonates, such as methyl vinyl carbonate (9) [50] carboxylic acid allyl esters, such as allyl acetate (10) allyl carbonates, such as allyl methyl carbonate (11) [51] and cyclic vinyl esters, such as a-angelica lactone (12) [52]). 

CsHsOs furan-2-carboxylic acid allyl ester 4208-49-5... 

SCHEME 38. Threo/erythro diastereoselectivity in the photooxygenation of allylic halides, sulphones, carboxylic acids and esters... 

Another interesting variant of Claisen rearrangement has been introduced by Ireland [149], and used by his group in carbohydrate chemistry. The starting compound is again an allylic alcohol that is esterified by a suitable carboxylic acid. This ester is enolized in basic medium, and quenching of the intermediate enolate at low temperature gives a ketene silyl... 

Chiral homoallylamines are valuable synthons for the preparation of biologically active components including P-amino carboxylic acids or esters, obtained by oxidation of the ally lie functionality.1-29 Because removal of the chiral auxiliary by hydrogenation leads to the loss of the allylic functionality, we developed alternative routes for the conversion of the adduct into the unprotected homoallylamines. As a typical example, (f ,f )-PGA-homoallylamine derived from isobutyraldehyde Hi was used to develop the so-called mroStrecker and the decarbonylation method for the conversion of (R)-phenylglycine amide protected homoallylamines into /V-benzylidene protected homoallylamines 15 (Scheme 25.7). 

Substituted 7-oxo-7//-pyrido[l,2,3-de]-l,4-benzoxazine-6-carboxylic acids and esters (197) were prepared when l-(l-substituted allyl)-l,4-dihy-... 

Preparation of 8-allyl-4-oxo-7-(2,2,2-trifluoro-acetylamino)-4H-chromene-2-carboxylic acid ethyl ester... 

Allyl-7-amino-4-oxo-4H-chromene-2-carboxylic acid ethyl ester (32 mmol) dissolved in 400 ml of CH2C12 was treated first with A.IV-diisopropylethylamine (50 mmol), then trifluoroacetic anhydride (50 mmol) while cooling the mixture in an ice bath. The mixture was stirred 1 hour at ambient temperature, then washed with 200 ml apiece 2M HC1, saturated NaHC03 solution, and brine, dried with Na2S04, and filtered. The material was concentrated and 12.2 g product isolated as a pale yellow solid, mp = 136-137°C. 

It is noteworthy that Takeda and coworkers (Ref. 154) recently proposed allyl isopropenyl dicarbonate made from isopropenyl chloroformate and sodium allyl carbonate as a convenient reagent for the preparation of allyl esters of carboxylic acids. Allyl isopropenyl dicarbonate reacts with carboxylic acids in the presence of DMAP under mild neutral conditions to give allyl esters in high yields. Allyl esters which could be deprotected by palladium catalysts are especially useful in the case of unstable compounds under acid or basic conditions, for example O-glycopeptides, penicillin derivatives, etc. 

In the laboratory of B.M. Trost, the second generation asymmetric synthesis of the potent glycosidase inhibitor (-)-cyclophellitol was completed using a Tsuji-Trost allylation as the key step. The synthetic plan called for the conversion of the a-nitrosulfone allylation product to the corresponding carboxylic acid or ester. Numerous oxidative Nef reaction conditions were tested, but most of them caused extensive decomposition of the starting material or no reaction at all. Luckily, the nitrosulfone could be efficiently oxidized with dimethyidioxirane under basic conditions (TMG) to afford the desired carboxylic acid in high yield. 

In order to treat influenza infections, the development of neuraminidase inhibitors is required. The currently available compounds are not potent enough, and they have a number of side effects. The stereoselective total synthesis of one potent inhibitor, BXC-1812 (RWJ-270201), was achieved by M.J. Muller and co-workers. The key intermediate substituted nitromethane was prepared via a Pd-catalyzed allylation of nitromethane under basic conditions. The transformation of this nitroalkane to the corresponding carboxylic acid methyl ester was carried out in two steps. The Nef reaction was conducted in DMF instead of the usual DMSO because DMSO as the solvent caused extensive epimerization of the product. The initially formed carboxylic acid was then esterified. 

An alternate route to fluoroolefins relies upon the ease of reduction of difluoroolefins(18). Reduction of 114 with sodium bis(2-methoxyethoxy)aluminum hydride (Scheme 35) afforded the fluoroolefins 115 and 116 considerably enriched with the (E)-isomer 116. In a complementary reaction, reduction of the allylic alcohol 117 with LiAlH4 afforded selectively the (Z)-isomer 118. The difluoromethacrylic acid (121) was prepared in similar manner from 120 (Scheme 36) (53 for related examples see references 75 and 76). Under more forcing conditions, further reduction afforded 3-fluoromethacrylic acid 122. Of more general use is the reaction of 120 with Grignard reagents whereupon the 1,4-addition elimination mechanism offers an entry into a-difluoromethylene substituted aliphatic and aromatic carboxylic acids 123. Ester enolates (125) have been shown to add to trifluoropropene (124) forming the difluoroolefins (126) (Scheme 37) (54). 

In the Ireland-Claisen rearrangement (equation 11.17), an allylic ester is converted to an enolate that reacts with trimethylsilyl chloride to produce an allyl trimethylsilyl ketene acetal, which then imdergoes rearrangement. Depending on the reaction conditions, the product may be a y,S-unsaturated carboxylic acid or ester. ... 

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