Methyl propynoate

The Diels-Alder cycloadclition reaction occurs most rapidly if the alkene component, or dienophile ("diene lover"), has an electron-withdrawing substituent group. Thus, ethylene itself reacts sluggishly, but propenal, ethyl propenoate, maleic anhydride, benzoquinone, propenenitrile, and similar compounds are highly reactive. Note also that alkynes, such as methyl propynoate, can act as Diels-Alder dienophiles. 

In the case of the reaction of 2-vinylindole (83, R = Ri = H) with methyl propynoate, a diester is obtained by a multiple one-pot process involving two molecules of the dienophile and the extrusion of ethene (Equation 2.23). 

Scheme 10.2 gives some examples of ene and carbonyl-ene reactions. Entries 1 and 2 are thermal ene reactions. Entries 3 to 7 are intermolecular ene and carbonyl-ene reactions involving Lewis acid catalysts. Entry 3 is interesting in that it exhibits a significant preference for the terminal double bond. Entry 4 demonstrates the reactivity of methyl propynoate as an enophile. Nonterminal alkenes tend to give cyclobutenes with this reagent combination. The reaction in Entry 5 uses an acetal as the reactant, with an oxonium ion being the electrophilic intermediate. 

Amouri and coworkers also demonstrated that the nucleophilic reactivity of the exocyclic carbon of Cp Ir(T 4-QM) complex 24 could be utilized to form carbon -carbon bonds with electron-poor alkenes and alkynes serving as electrophiles or cycloaddition partners (Scheme 3.17).29 For example, when complex 24 was treated with the electron-poor methyl propynoate, a new o-quinone methide complex 28 was formed. The authors suggest that the reaction could be initiated by nucleophilic attack of the terminal carbon of the exocyclic methylene group on the terminal carbon of the alkyne, generating a zwitterionic oxo-dienyl intermediate, followed by proton transfer... 

Zirconium tetrachloride promotes a tandem nucleophilic addition and aldol-type condensation reaction of methyl propynoate, or /V,/V-dimethylpropynamidc, with aldehydes, or ketones, in the presence of tetra-n-butylammonium iodide (Scheme 6.13) [8] with a high selectivity towards the formation of Z-isomers. A similar reaction occurs between aliphatic and aromatic aldehydes and penta-3,4-dien-2-one to yield 1-substituted 2-acetyl-3-iodobut-3-enols (50-75%) [9]. 

Methyl propynoate adds to 5,6-dimethylidenebicyclo[2.2.1]heptan-2-one (1) with... 

A variant on the traditional method is to use a phenylhydroxylamine instead of a phenylhydrazine. For example, A-(benzyloxycarbonyl)-phenylhydroxylamine can be reacted with methyl propynoate to give an adduct that spontaneously undergoes a [3,3]-sigmatropic shift and eventually yields l-(benzyloxycarbonyl)-3-(methoxycarbonyl)indole (Scheme 7.15). 

Section IV,A,2 Competition between van Alphen-Huttel rearrangement and ring opening to a vinyldiazo compound is found to be substituent dependent for transient spiro-3//-pyrazoles formed from methyl propynoate and 4-diazopyrazolones.177... 

N-Substituted arylhydroxylamines add to methyl propynoate and rearrangement occurs to give indolc-3-carboxylate esters[3]. With unsubstituted... 

Another remarkable synthesis of 2,4-dicarboxythiophenes in high yield involves a unique dimethylsulfonium butadiene (34), which could be cyclized to 2,4-dimethoxycar-bonylthiophene (35) in 91% yield by standing overnight in thionyl chloride (66CB1558). The crystalline salt (34) was obtained in satisfactory yields by refluxing two equivalents of methyl propynoate with one equivalent of dimethyl sulfoxide in ethanol. 

A synthesis of the 3-methylthiopyran-2-one (337) is based on the formation of a 2 1 adduct (336) between methyl propynoate and DMSO which occurs at high ester concentrations (Scheme 102) (66CB1558). Upon heating, cyclization occurs with the overall loss of methoxymethane. Only a small amount of dimethyl furan-2,4-dioate is formed in this reaction, but a furan is the sole product from dimethyl butynedioate and DMSO. 

Methyl-5-propyl-1,2-4-trioxolane, see trans-2-Hexene ozonide, 2507 f Methyl propynoate, Methyl propargylate, see Methyl propiolate, 1438... 

Water is essential for this reduction. This system reduces alkynes to rij-alkenes with high stereoselectivity. Addition of methyl propynoate (10 mole %) increases the reactivity and can effect reduction of alkynes to alkanes. 

Irradiation of a mixture of hexafluorobut-2-yne (10) and dimethyl disulfide (II) yields the addition product 12 as a mixture of E- and Z-isomers.51 In contrast, when trifluoromethancthiol (14) reacts with methyl propynoate (13) under photochemical conditions, the Z-isomer is formed preferentially.52... 

An analogous process for stereospeeific generation of 1,4-dienes using allylcopper reagents has also been reported. Thus reaction of 2 eq. of allylcopper in ether at - 78° under Nj with methyl propynoate (6) gives methyl rrani-2,5-hexadienoale (7). 

Prepared in a single step by sequential treatment of methyl propynoate in THF at -78° with -butyllithium. hexanal, and irimcthylchlorosilane (71 % yield). 

Vicinal diols in sugar substrates can also be protected as their 2-(ferf-butoxycarbonyl)-ethylidene ( Bocdene ) or 2-(methoxycarbonyl)-ethylidene ( Mocdene ) derivatives in the reaction with ferf-butyl or methyl propynoate. The acetal-like structures of these protecting groups is of interest because they are stable under acidic conditions, which allows their selective deprotection versus other acetals, and can be removed under basic conditions via an addition-elimination mechanism (O Scheme 21) [140]. The procedure is not suitable for 1,3-or 1,4 diols. 

Maleic anhydride Benzoguinone Propenenitrile (Acrylonitrile) Methyl propynoate... 

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