Dimethylacetylene carboxylate

The treatment of azocine 44 (R1 = R2 = Me) with potassium followed by dichloromethane, afforded homoazocines 49 and 50. In a similar manner, 137 and 138 yielded 142 and 141, respectively.71 The reaction of the 1,4-dihydropyridine 214 with two equivalents of dimethylacetylene carboxylate gave the cyclobutenoazocine 215.403... 

The polysulfide species [Mo=S(S4)2] (20 in Scheme 2.19) was reported to react with an alkyne producing a metal dithiolene unit in situ. The metal insertion reaction proceeds via electrophilic attack by dimethylacetylene-carboxylate (DMAC). It was observed that replacing the sulfido ligand with an 0X0 makes the tetrasulfide ligand less reactive towards the electrophilic attack by DMAC and changes the product of the reaction of DMAC and complexes possessing a Mo(S4) as shown in Scheme 2.19. 

In an extension of earlier work, Buigada et al. have also reported on the reaction of the cyclic phosphite (66) with dimethylacetylene dicarboxylate (58) in the presence of proton sources such as carboxylic acids, amide N-H bonds in succinimide or phthalimide and amine N-H bonds in p UTole or indole. With carboxylic acids (67) a mixture of the ylid (68) and the cyclic phosphorane (69) was obtained and in some instances (e.g. with 2,4,6- trimethylbenzoic and p-methoxybenzoic acids) the ylid and phosphorane were shown to be in equilibrium. With amides as the proton source, ylids were generally formed although with N-methylbenzamide (PhCONHMe)a signal attributed to (70) was observed at = - 52 p.p.m. which had disappeared by the end of the reaction through rearrangement to (71). With amines (e.g. pyrrole) the products were again a mixture of ylid (72) and phosphorane (73) and the entire set of results was rationalised in terms of HSAB theory and the symbiotic effect around phosphorus. 

A number of investigators have synthesized benzazocine derivatives by treating reduced quinolines and isoquinolines with dimethylacetylene di-carboxylate (DMA) or with other acetylenes (Eqs. 6-9).274-277... 

Synthesis of the acyclo C-nucleoside 147 was achieved by [3+2] cycloaddition of thiazolo[3,4-c]oxazole C-nucleoside 145 onto dimethylacetylene di-carboxylate (94M189) (Scheme 44). 

The geometrical characteristics, determined by X-ray diffraction, for systems —C=C—in which acetylene is directly bonded to R = C=C (ethylenic), C==C (aromatic), C=0 (ketones and carboxylic acids), C=N and to other C=C bonds are collected in Table 5. In Table 6, we summarize the results of accurate ED studies of dimethylacetylene , vinylacetylene, propynaP and diacetylene which were designed to study the effects of conjugation in these systems. 

Palladium catalysts have been used for cycloaddition of dimethylacetylene di-carboxylate (DMAD) to polycyclic arynes 3, 77 and 79 (Schemes 34-36). All these reactions exhibit the same reactivity pattern as is observed in the [2+2+2] cycloaddition of benzyne to DMAD (see Sect. 3.1) Pd2(dba)3 leads selectively to the cocycloaddition of one molecule of aryne and two molecules of DMAD, while Pd(PPh3)4 induces the reaction of two molecules of aryne with one molecule of DMAD. Both reactions afford the corresponding polycyclic aromatic hydrocarbons in good yields and with high chemoselectivity, constituting a novel and versatile method for the synthesis of functionalized PAHs under mild reaction conditions [70-72] (Scheme 34). 

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