Selenolic acid esters carboxylic acids

Selenolic acid esters from carboxylic acid chlorides COCl -> COSeR... 

Example 2, in addition to oxyselenide formation, carbo- and heteroseleno cycliza-tion, A -PSP can be used to generate selenides from alcohols and selenol esters from carboxylic acids, respectively, in the presence of a stoichiometric amount of n-Bu,P. ... 

Alkyl phenyl setenides selenol esters. N-PhcnylscIcnophthalimidc is superior to aryl selenocyanates for conversion of alcohols to alkyl phenyl selenides (6, 252-253) and of carboxylic acids to selenol esters (7, 396-397). When conducted in the presence of an amine the latter reaction provides amides in high yield (equation l). ... 

Selenolate 77, prepared from diselenides with sodium borohydride, is also not reactive enough for reactions with esters or lactones. Only under higher reaction temperatures, lactones 90 can be ring opened with selenolates to the corresponding carboxylic acids 91.173,174 The selenium moiety can then be used for further manipulations. Using similar reaction conditions, esters 92 can be converted to the corresponding carboxylic acids 93 and selenides 94 (Scheme 21).149... 

Selective activation of carboxylic acids. Carboxylic acids add exclusively to the triple bond of 1 to form an adduct (a) that rearranges to the (Z)-enol ester 2. Hydroxyl, phenolic, amino, and mercapto groups do not react with 1 under the same conditions. The esters (2) react with alkali metal salts of thiols and of selenophenol in THF at 0° to form thiol and selenol esters (3). 

Selenolate 1 [1,2], prepared from diphenyl diselenide by reduction with NaBH4 in ethanol, is not reactive enough towards esters and lactones. However, application of more rigorous conditions, i. e. at 110-120 °C in dry DMF for lactones 15, affords the corresponding ring-opened products, cu-phenylselenyl carboxylic acids 16, in good yields [44]. Compounds 16 can be easily converted to co-ole-finic methyl esters 17 by treatment with diazomethane followed by oxidative elimination of the phenylseleno group (Scheme 25). By contrast, the uncomplex-... 

It has been reported that some selenols are directly acylated by carboxylic acids to give selenol esters. " For example, heating of 4-hydroselenobutyric acid at about 160 C resulted in ring closure to give the corresponding y-lactone (equation 1). ... 

A mild and convenient method has been attained by using the imidazolide (8 equation 6) or triazolide (9 equation 7) of carboxylic acids as a key intermediate. Treatment of an imidazolide of carboxylic acid with 1.2 equiv. of benzeneselenol and 0.02 equiv. of sodium phenoxide provided the selenol ester in a quantitative yield. In the case of the triazolide of carboxylic acids, the reaction proceeded in the absence of base.2 ... 

Reaction of some vinyl esters (10 Scheme 3) of carboxylic acids with selenolate gave the corresponding selenol esters in high yields because of the good leaving ability of enolate. ... 

Reaction of carboxylic acids with phenyl dichlorophosphate, followed by the addition of bensenesele-nol to the mixture afforded selenol esters (Scheme 4). The reaction is assumed to proceed via the penta-covalent oxyphosphorane intermediates (11a) and (11b). 

It has been reported that aryl selenocyanate (25 Scheme 7) reacts with carboxylic acids in the presence of tributylphosphine under mild conditions, giving rise to selenol esters in good yields. The process may involve the reaction of carboxylic acids with selenophosphonium salt (26), which is the key intermediate. 

Diaryl diselenides reacted with carbon monoxide (5-100 atm) at 100-200 °C, in the presence of Co2(CO)s as a catalyst, to give the corresponding selenol esters of aromatic carboxylic acids in 21-96% yields (equation 14)P... 

A new method for the transformation of —CO2H to —H has been attained by formation of the selenol ester from carboxylic acid, followed by its reduction. Owing to high chemoselectivity and mild reaction conditions, this method is often utilized for the synthesis of natural products (equation 21). ... 

Seleno-Carboxylic Acid Esters (Selenol Esters).Ill... 

Keywords Chalcogeno carboxylic acid ester Thiol ester Selenol ester Tellurol ester... 

Seleno-carboxylic acid esters (selenol esters) 2 are also prepared like thiol esters by the reaction of acyl halides with selenols, or diselenides as well as their alkali metal salts. Most of the preparative methods for thiol esters shown in Sect. 2.1 are applicable to the synthesis of selenol esters 2. Unique synthetic... 

Like selenol esters, tellurol esters can also serve as acyl transfer reagents, giving rise to the corresponding ketones, carboxylic acids, and esters. For example, tellurol esters react with lithium dialkylcuprates at -78 °C to give the corresponding ketones in high yields (Eq. 63) [117]. 

Selenol esters were also hydrolyzed to carboxylic acids, but thiol esters are inert under similar conditions. The nature of the copper salt has a dramatic influence on the reaction course. No hydrolysis products were obtained when tellurol esters were treated with copper sulfate or copper(l) chloride. 

Phenyl selenocyanate, CoHsSeCN. Mol. wt. 182.08, b.p. 125°/16 mm. Preparation. Selenol esters, RCOSeCeH. Carboxylic acids react with phenyl selenocyanate (1 equiv.) and tri-n-butylphosphine (2 equiv.) in methylene chloride or THF to form phenylselenol esters usually in high yield. Similarly, thiol esters,... 

Thiol and selenol esters. These useful intermediates in the synthesis of complex molecules can be prepared in good to high yields by activation of carboxylic acids with N,N -carbonyldiimidazole or N,N -carbonyldi-1,2,4-triazole (1, 116 2, 61). The products, without isolation, react with thiols or selenols to form the esters (equation I). ... 

TMol(selenol) esters. Activated enol esters (2) of carboxylic acids can be prepared as shown in equation (I). They can be converted into thiol and selenol esters (3). 

Macrolactonization has been accomplished using Thiol and selenol esters can also be prepared in one pot from carboxylic acids using (1) reaction of the intermediate (2) with aromatic thiols or selenols is complete within a few minutes in DMF, while aliphatic thiols require a few hours. Formation of the phenylthiol ester of IV-Cbz-L-phenylalanine was accompanied by only slight racemization. N,N -Carbonyldi-sym-triazine can be used in place of (1), with similar results. 

Aliphatic nitriles react slowly with phenols and phenyl ethers in the presence of trifluoromethanesulphonic acid to give ketones after hydrolysis, in a variation of the Houben-Hoesch reaction. The crystalline complex of copper(i) triflate and benzene induces the acylation of aromatic substrates with selenol esters, affording a transition-metal mediated version of the Friedel-Crafts reaction. Aromatic carboxylic acids can be converted into symmetrical diaryl ketones in good yield by treatment of their 5-(2-pyridyl)thioesters with bis-(l,5-cyclo-octadiene)nickel [equation (15)]. In contrast to other methods for preparing symmetrical aromatic ketones, this method allows their preparation from a single starting material. 

Nucleophilic substitution, e.g. the preparation of thiocyanates from lipophilic alcohols, can be facilitated by substrate hydrophilation via ammonioethanesulfonic acid esters (betylates)i . Mercaptans can be easily prepared from alcohols with inversion of configuration via thiolic esters prepared with thioacetic acid in the presence of 2-fluoro-pyridinium salts . C-Sulfenylation of / -dicarbonyl compounds with mercaptans by air oxidation in the presence of tetraethylammonium fluoride has been reported . Activated thiolic and selenolic esters can be prepared at room temperature from carboxylic acids and aryl thiocyanates or selenocyanates in the presence of tri-n-butylphosphine i. Phenylselenolactones have been obtained under very mild conditions from unsaturated acids and benzeneselenyl chloride. ... 

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