Dimethyl acetylene dicarboxylate structures

Mesoionic 4-amino-l,2,3,5-thiatriazoles constitute the only class of mesoionic 1,2,3,5-thiatriazoles known. They are prepared by the reaction of l-amino-l-methyl-3-phenylguanidine with approximately 2 equivalents of thionyl chloride with pyridine as solvent (88ACS(B)63>. They are obtained as the yellow 1 1 pyridine complexes (17). The dark-violet mesoionic 1,2,3,5-thiatriazole (18) was liberated on treatment with aqueous potassium carbonate (Scheme 3). The structure is established on the basis of elemental analysis and spectroscopic data. In particular, the IR spectrum is devoid of NH absorptions. Compound (18) exhibits a long-wavelength absorption at 463 nm in methanol. When mixed with an equivalent amount of pyridinium chloride, complex (17) is formed and the absorption shifts to 350 mn. The mesoionic thiatriazoles are sensitive towards mineral acids and aqueous base and although reaction takes place with 1,3-dipolarophiles such as dimethyl acetylene-dicarboxylate, a mixture of products were obtained which were not identified. 

The [18]crown-6 (/) complexes with dimethyl acetylene dicarboxylate (1 1) U), malo-nodinitrile (1 2) 12), and benzenesulfonamide (1 2)13) were the first to be revealed by X-ray structural analyses. Figures 4-6 show the stereochemistry of these neutral complexes within the crystal1. In the first two complexes the CH3 and CH2 groups... 

Cycloaddition reactions were performed by heating of 60-62 with dimethyl acetylene dicarboxylate (DMAD) in toluene to reflux under a nitrogen atmosphere. The structures of the isolated products 63-69 are depicted in Fig. 9. Their yields are summarized in Table 1. 

In a related study,(101) was shown to give cycloadducts (103) when reacted with (102), and it gave (105) with hexafluoroacetone, (106) with phenylisothiocyanate and interestingly, (107) was obtained with dimethyl acetylene-dicarboxylate and water. The structures were all confirmed by X-ray crystallography. 

It is possible to compare the reactivity of some 1,3-dipoles inserted in cyclic structures with that of the same dipoles in open chains. This comparison, recalling that between cyclic and open-chain dienes (Section 4.1.3), is limited to two classes of 1,3-dipoles without a double bond , namely azomethine imines and oxides. For the former, there are data in Table 12 for the reaction with dimethyl acetylene dicarboxylate (iii) the cyclic azomethine imine (sydnone) is about 300 times less reactive than the open-chain cyanoazo-methine imine. In the case of nitrones, a typical comparison is. for reaction with ethyl crotonate in toluene at 100°C "... 

A common dipolarophile for the Pechmann pyrazole synthesis is dimethyl acetylene dicarboxylate (DMAD, 41), a highly electron-deficient alkyne. Spring and co-workers used the 1,3-dipolar cycloaddition between DMAD and a fluorous-tagged diazoacetate (40) as part of studies aimed at production of structurally diverse scaffolds. As expected, the reaction proceeded efficiently to produce 42 in high yield. 

Photochemistry.— The photochemical addition of dimethyl acetylene-dicarboxylate, methyl propiolate, or methyl phenylpropiolate to benzo[h]-thiophen and its 2- and 3-methyl and 2,3-dimethyl derivatives leads to cyclobutene derivatives of unexpected structures. From benzo[ >]-thiophen and dimethyl acetylenedicarboxylate (376) is obtained. Methyl propiolate adds in a direction opposite to that of methyl phenylpropiolate, suggesting that the excited state of benzo[h]thiophen is highly polarized. The mechanism of the addition is discussed, and several mechanistic alternatives are suggested. Only with diphenylacetylene, which reacts slowly, can the normal addition product (377) be obtained. The... 

Jurczak has shown that cycloaddition reactions involving furan could also be catalyzed by transfer RNA under high pressure [13]. Flence, kinetin 9 reacts with maleic anhydride and dimethyl acetylene dicarboxylate (DMAD) at lOkbar showing that tRNA is a true Diels-Alderase (Scheme 2). These products are not formed at high pressure without tRNA. It seems that a conformation of tRNA induced at high pressure meets structural requirements of a transition state of Diels-Alder reaction. It provides complementarity of size and shape of both substrates and is a driving force in molecular recognition. 

These Michael-type products are similar to structures obtained by Kotsuki [36] by cycloaddition reactions of N-sub-stituted pyrroles 94 with dimethyl acetylene dicarboxylate. If the substituent on the nitrogen is electron donating (R=Me), a primary 1 1 Diels-Alder cycloadduct 95 reacts further to give Michael-type reaction product 96 (Scheme 23). Described substituent influence on the susceptibility of 7-azabicyclo[2.2.1]hept-2-enes to Michael reaction is in good accord with results obtained by Scheeren [37] who has shown that the hi -pressure Diels-Alder reaction of 3-thiosubstituted N-carbomethoxypyrrole derivatives with electron-poor alkenes (12kbar, MeCN, 50°C, 16h) affords 2-thiosubstituted 7-azabicyclo[2.2.1]hept-2-enes in high yields. 

Interesting role of pyridine in dipolar cycloadditions was provided by Matsumoto [84]. High-pressure reaction of 2-halogenopyridines with dimethyl acetylene dicarboxylate provided 1 2 adducts 9aH-quinolizines 229 and 4H-quinolizines 230 (Scheme 55). The reaction mechanism includes [3 + 2] cycloaddition reaction in the first step nucleophilic attack of the nitrogen heterocycle form a 1,5-dipolar intermediate 228 which combines with the second molecule of the DM AD giving a cyclic product 229. In the case of fluorine substituent, 1 3 adduct of xmknown structure is formed in 5.3% yield. 

Suggest structure of anticipated products of the reaction of isotetralin with dimethyl acetylene dicarboxylate. 

Various Carbocyclo-fused Systems. - The adduct (337), obtained from 4,6-diphenyl-4H-cyclopenta[b]thiophen and dimethyl acetylene-dicarboxylate, yields (338) upon heating to 115°C. The structure of (338) was determined by X-ray crystallography. Further heating leads to isomerisation of (338) to (339) and (340). 

Selenourea and 1-aryl and 1,3-diaryIselenoureas reacted with acetylene-dicarboxylic acid and its dimethyl ester to give 3,4-dihydro-2-imino-2/f-l,3-selenazin-4-one-6-carboxylic acid derivatives, e.g., 220 and 221. The structure of 221 was deduced from that of its hydrogenation product 222. ... 

A further reaction of the starting cluster is the coordination of /7A(dimethyl)ace-tylene dicarboxylate, which again involves the unique bridging hydride. In this case, both of the cluster hydrides are transferred to the same acetylenic carbon of the alkyne, so that the coordination of the resulting dihydro-derivative is through a single carbon, giving the carbene-complex with the structure shown in Fig. 21. 

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