Alkynyl carboxylates synthesis

More recently we have reported the preparation of alkynyl esters by the reaction of lithium alkynolates with the corresponding acid chlorides (equations 14 and 15, Section II.B.2). This method works well for the synthesis of alkynyl phosphates, however, it has only limited applicability in the preparation of alkynyl carboxylates. ... 

Scheme 3.24 Cu-catalyzed decarboxylative coupling of alkynyl carboxylic acids (a) and decarboxylative furan synthesis (b), as described by Xue and coworkers [41].

The authors reported also one example that demonstrated the suitability of the method also for the synthesis of enol lactones starting from alkynyl carboxylic acids. Also in this case, due to the mechanism involving a Rh-vinylidene complex, the approach is limited to terminal alkynes. 

The heteroatom-substituted carbene complexes most frequently used in organic synthesis are carbonyl complexes of the type (CO)5M=C(X)R (M Cr, Mo, W X OR, NR2 R H, alkyl, aryl, vinyl, alkynyl, etc.). To some extent such complexes behave as carboxylic esters or amides, the (CO)5M=C group having electronic properties similar to those of a carbonyl group (Figure 2.16). 

In addition, iodine snccessfnlly catalyzed the electrophilic snbstitntion reaction of indoles with aldehydes and ketones to bis(indonyl)methanes [225], the deprotection of aromatic acetates [226], esterifications [227], transesterifications [227], the chemoselective thioacetalization of carbon functions [228], the addition of mercaptans to a,P-nnsatnrated carboxylic acids [229], the imino-Diels-Alder reaction [230], the synthesis of iV-Boc protected amines [231], the preparation of alkynyl sngars from D-glycals [232], the preparation of methyl bisnlfate [233], and the synthesis of P-acetamido ketones from aromatic aldehydes, enolizable ketones or ketoesters and acetonitrile [234],... 

A synthesis of [3]-fused furans involving a ring enlargement can be effected by the treatment of a-alkynyl-a-cyclopropylcycloalkanones with an electron-rich Au(l) catalyst in the presence of a suitable nucleophile (Equation 18) <2006AGE6704>. The nucleophiles that can be used include alcohols, phenols, carboxylic acids, indole, and 2-pyrrolidone. Open-chain ketones as well as other ring sizes react with comparable yields. Silver and lanthanide triflates are also effective catalysts for this transformation. 

A concise synthesis of highly substituted furans, pyrroles, butenolides, and 2-butene-4-lactam esters starts from alkynyl adducts of a Fischer carbene complex 21 (Scheme 27) < 1998JOC3164>. Incorporation of an aldehyde yields a reactive vinyl tungstencarbonyl complex 22 that can be oxidatively transformed to an ester group, furnishing the furan carboxylic ester 23. 

Alkynylepoxides [123,142,143 Eq. (68) 142] and alkynyl propiolactones [Eq. (69) 144] afforded allenyl-alcohols or allenyl-carboxylic acids. Diastereoselective ring opening of alkynylepoxides has been studied [143,145]. The use of optically active propargyl substrates enables the synthesis of optically active allenes [Eq. (70) 146] [10,140,145-147]. A subtle change of the reaction medium may drastically change the degree of chirality transfer, which has been systematically examined [145]. 

For the synthesis of the 2-alkynyl derivatives, three different approaches have been used, owing to different reactivity of the side chains or separative problems during purification. Briefly, from the common intermediate, the 5 -carboxyl-2, 3 -isopropyliden derivative, the two carboxamido derivatives 1 and 5 were obtained as starting material for the synthetic routes a-d depicted in Scheme 1. In any case the introduction of the alkynyl chain was carried out by a modification of the classical cross-coupling reaction catalysed by palladium. 

A-tosylhydrazones (equation 2) [52]. The reaction can also be executed in one pot from arylhalide, aldehyde, and tosyl hydrazine. A novel 2-arylindole synthesis that was discovered by Rashinkar entails the Pd-catalyzed reaction of o-nitrobenzyl cyanides with arylboronic acids (equation 3) [53]. Tobisu and Chatani accomplished the direct Pd-catalyzed alkynylation of anihdes leading to indoles (equation 4) [54], Lee and colleagues induced nitriles into becoming indole-3-carboxylates through the Blaise reaction (equation 5) [55]. 

Iodine-catalyzed and solvent-controlled selective method for the synthesis of iodopyrano[4,3-6]quinolines and o-alkynyl esters from o-alkynyl aldehydes in mild reaction conditions is developed for the first time by Verma et al. This novel oxidative esterification provides a powerful tool for the preparation of a wide range of functionalized pyranoquinolinones as well as isocoumarins, and it is applicable for a variety of functional groups including primary alcohol, carboxyl, and methoxy groups. 

The enantioselective synthesis of axially chiral hydroxy carboxylic acid derivatives 42 was accomplished by the cationic rhodium(I)/BINAP complex-catalyzed [2 + 2 + 2] cycloaddition of a,w-diynes 40 with 2-alkoxynaphthalene-derived alkynyl esters 41 with high yields and ee values (Scheme 9.15) [17],... 

In 2006, Asao and Sato developed the synthesis of 9-acylanthracenes 60 by the gold(I)-catalyzed reaction of ( -alkynyl(oxo)arenes 58 with benzyne, generated from benzenediazonium 2-carboxylate 59 (Scheme 28.22) [33]. The reaction proceeds through [4 - - 2] cycloaddition between benzyne and benzopyrylium auricate complex 61, arising from the gold-induced cyclization of 58. 

---