Carbon methyl propiolate

A more conventional cycloaddition occurs with activated acetylenes, however, the intermediate cyclobutene adducts undergo rearrangement to give insertion of two carbon atoms into the enamine chain (55). Thus the enamine (16) reacted with methyl propiolate to give the dienamino ester (73), presumably via the cycloaddition product (65a). 

FIGURE 8.20 Peptides activated at an IV-methylamino-acid residue are postulated to epimer-ize because of the formation of the oxazolonium ion. Evidence for the latter resides in spectroscopic studies,96 and the isolation of a substituted pyrrole that was formed when methyl propiolate was added to a solution of Z-Ala-MeLeu-OH in tetrahydrofuran 10 minutes after dicyclohexylcarbodiimide had been added.95 The acetylenic compound effected a 1,3-dipolar cycloaddition reaction (B), with release of carbon dioxide, with the zwitter-ion that was generated (A) by loss of a proton by the oxazolonium ion. 

The meso-ionic l,3>2-oxathiazol-5-ones (169) show an interesting range of reactions with nucleophiles including ammonia, primary amines, and aqueous alkali. They also react with l,3-dipolarophiles, including dimethyl acetylenedicarboxylate and methyl propiolate, yielding isothiazoles (171) and carbon dioxide. 1,3-Dipolar cycloaddition reactions with alkenes such as styrene, dimethyl maleate, and methyl cinnamate also lead to isothiazoles (171) directly. BicycUc intermediates (cf. 136) were not isolable these cycloaddition reactions with alkenes giving isothiazoles involve an additional dehydrogenation step. 

Dumitrascu and co-workers (52) transformed 4-halosydnones into 5-halopyr-azoles by cycloaddition with DMAD and methyl propiolate followed by retro-Diels-Alder loss of CO2. Turnbull and co-workers (194) reported that the cycloadditions of 3-phenylsydnone with DMAD and diethyl acetylenedicarboxylate to form pyrazoles can be achieved in supercritical carbon dioxide. Nan ya et al. (195) studied this sydnone in its reaction with 2-methylbenzoquinone to afford the expected isomeric indazole-4,7-diones. Interestingly, Sasaki et al. (196) found that 3-phenylsydnone effects the conversion of l,4-dihydronaphthalene-l,4-imines to isoindoles, presumably by consecutive loss of carbon dioxide and A-phenylpyrazole from the primary cycloadduct. Ranganathan et al. (197-199) studied dipolar cycloadditions with the sydnone 298 derived from A-nitrosoproline (Scheme 10.43). Both acetylenic and olefinic dipolarophiles react with 298. In... 

The reaction of the quaternary compound (16) with carbon nucleophiles results in attack at sulfur leading to an open-chain intermediate that recyclizes to ring-expanded compounds (79TL1281). Reaction of (16) with one equivalent of cyanide ion proceeds according to Scheme 4 to produce (17) in high yield. When an excess of cyanide ion is employed, (17) reacts further to form 80% of a compound whose structure is represented by either (18) or (19). The reaction of (16) with methyl propiolate anion produces (20) via a similar process. 

Methyl propiolate and DMAD add to carbon diselenide under high pressure to give 1,4,5,8-tetraselenafulvalenes (101) and (102). The dimerization of a l,3-diselenole-2-carbene is implicated (81CC669). The alkynes function as the two-atom unit while carbon diselenide is the three-atom unit. 

Reaction of l-amino-3-benzyloxypyridinium mesitylenesulfonate 755 with methyl propiolate in the presence of potassium carbonate in DMF at room temperature gave a mixture of methyl 4-benzyloxy- 756 and 6-benzyloxypyr-azolo[l,5- ]pyridine-3-carboxylates 757 (Scheme 95) <1996H(43)2249>. Treatment of 756 and 757 with 48%... 

Several uncatalyzed [2+2] cycloadditions of allylsilanes to highly activated carbon-carbon and carbon-heteroatom bonds were reported before and during 1990 [493]. The first example of Lewis acid-promoted [2+2] cycloaddition of allyltrimethylsilane was introduced by Snider et al. in 1979 [494]. They reported fhat the AICI3-promoted reaction of methyl propiolate with allyltrimefhylsilane forms a cyclobutene. In fhe last decade similar cycloadditions to a variety of electron-deficient unsaturated bonds have been developed for efficient syntheses of cyclobutanes, cyclobutenes, oxetanes, and azetidines, as described below. 

Pyrone reacts readily as a diene in Diels-Alder additions, but the initial adduct often loses carbon dioxide, generating a second diene that then adds a second mole of the dienophile reaction with maleic anhydride, shown below, is typical - a monoadduct can be isolated, which under more vigorous conditions loses carbon dioxide and undergoes a second addition. When the dienophile is an alkyne, methyl propiolate for example, benzenoid products result from the expulsion of carbon dioxide. Primary adducts, which have not lost carbon dioxide, can be obtained from reactions conducted at lower temperatures under very high pressure or in the presence of lanthanide catalysts. A useful example is the reaction of 2-pyrone and substituted derivatives with alkynyl boronates leading to aryl boronates 2-pyrone itself reacts in 86% yield with trimethylsilylethynyl boronate. ... 

Potassium carbonate and triethylamine converts 2-methoxycarbonylmethyl-3-methylthiazolo[3,2-c][l,2,3]triazolium bromide (160) into the yellow azomethine ylide (161) which reacts with methyl propiolate to give a mixture of (2E,4Z) and 2E,AE) isomers of methyl 4-methoxycarbonyl-5-(thiazol-2-yl)-2,4-hexadienoate (162) and (163) beside traces of 6-methoxycarbonyl-5-methoxy-carbonylmethyl-7-methylpyrrolo[2,l-i]thiazole (164) (Scheme 12) <94H2017>. 

The five-coordinate hydride-dihydrogen complex [OsH(T)2-H2) (CO)(P Pr3)2]BF4 acting as a template for the carbon-carbon coupling between methyl propiolate and 1,1-diphenyl-2-propyn-l-ol... 

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