Methyl 3-propynoate, reaction

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]. 

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. 

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). 

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. 

Tetracyanoethene, dimethyl acetylenedicarboxylate, methyl propynoate, maleic anhydride, 4-methyl- and 4-phenyl-4//-l,2,4-triazole-3,5-diones, are the most frequently used dienophiles in the application of the homo-Diels-Alder reaction. 

The reaction of norbornadiene with methyl propynoate was also performed at room temperature in the presence of aluminum trichloride and benzene. The major product under these conditions was the exo [2 + 2] cycloadduct 4. - ... 

The homo-Diels-Alder adduct of two molecules of norbornadiene to methyl propynoate 6 was isolated in very low yield (3%) in the above reaction it is however possible, by the use of high-pressure conditions, to effect this second cycloaddition with a yield of 60%. ... 

When complexes 37a,b reacted in pentane solution at — 78°C under an atmosphere of CO with dmad (Scheme 8), the butenolide complexes 38a,b were formed in clean reactions and could be isolated in 85 and 65% yields, i.e. the reaction proceeded with complete chemoselectivity for the Fe-0=C fragment. When the same reaction was performed at — 50 °C and — 30°C, respectively, with methyl propynoate (mp) as dipolarophile, the butenolide complexes 39a,b with the hydrogen next to the inserted carbonyl group were formed with complete chemo- and regio-selectivity. Complexes that had incorporated two moles of the alkyne (40a,b) were observed as minor side-products. In the absence of CO, and with two equivalents of mp, the tricyclic complexes 40a,b were formed exclusively in moderate yields. Complexes 40a,b can also be prepared in almost quantitative yields by irradiation of the corresponding complexes 39a,b in the presence of an excess of mp at room temperature, an observation that strongly supports the pathway indieated in Scheme 8. X-Ray structural analysis of 40b has confirmed that, of the possible regioisomers, only the one shown in Scheme 8 is formed. 

Investigation of [2 -l- 2] photocycloaddition of enones to monosubstituted alkynes indicates that the reaction proceeds with an opposite regioselectivity compared to that of alkenes [71]. Generally, head-to-head adducts are major products except when the group substituted on the alkyne is -CO2R or -OR (see Scheme 17). Thus, methyl propynoate (60, R = CO2CH3) photoadds to cyclopentenone 59 to give 1 1 HH and HT products. Cycloaddition of cyclohexenone to 1-hexyne has also been studied and the HH HT ratio varies from 2 1 to 7 1 as a function of substituents at the enone 3-position. It... 

Z)-3-lodo-2-(hydroxyalkyl)acrylates. ZrCl mediates the reaction of methyl propynoate and a carbonyl compound in the presence of Bu NI. This process is analogous to the Baylis-Hillman reaction, with the difference being that iodine is incorporated. 

A sequence of Diels-Alder and homo-Diels-Alder reaction occurs to furnish the cage compounds 81a -i when a solution of 11a -e in toluene is subjected to reaction with alkynes. Suitable alkynes are acetylene itself, phenylacetylene, methyl propynoate, and cyclooctyne [70]. 

The reaction of acetone, cyclopentanone, and cyclohexanone oximes with methyl propynoate (MeOH, 55°C-60°C) affords a mixture of products among which... 

The Pechmann and Knoevenagel reactions have been widely used to synthesise coumarins and developments in both have been reported. Activated phenols react rapidly with ethyl acetoacetate, propenoic acid and propynoic acid under microwave irradiation using cation-exchange resins as catalyst <99SL608>. Similarly, salicylaldehydes are converted into coumarin-3-carboxylic acids when the reaction with malonic acid is catalysed by the montmorillonite KSF <99JOC1033>. In both cases the use of a solid catalyst has environmentally friendly benefits. Methyl 3-(3-coumarinyl)propenoate 44, prepared from dimethyl glutaconate and salicylaldehyde, is a stable electron deficient diene which reacts with enamines to form benzo[c]coumarins. An inverse electron demand Diels-Alder reaction is followed by elimination of a secondary amine and aromatisation (Scheme 26) <99SL477>. 

To the ketene silyl (thio)acetal (1 equiv.) was added at room temperature neat ethyl propynoate, dimethyl acetylenedicarboxylate or etliynyl methyl ketone (1 equiv.). The mixture was stirred for 5 h at room temperature. The volatile products were removed at room temperature in vacuo (0.1 Torr) for 30 min. Purification of the crude reaction mixture by silica gel column chromatography (ethyl acetate-hexane, 5 95) afforded cycloadducts. 

Toward this goal, a furane ring was included in the carbonyl or amine component, since this moiety will furnish a highly reactive diene for the following IMDA. In most cases 2-furaldehyde (or the corresponding 5-methyl derivative) was employed. The acid component was chosen in order to introduce an activated dienophile suited for the IMDA and was in turn a fumaric acid monocarboxyamide [82, 84], a maleic or fumaric acid monoester [84] or a 3-substituted propynoic acid [83]. Benzylamine (or a para-substituted derivative) [81-83] or t-butylamine [83] have been chosen as amine component for the Ugi reactions. 

The reaction of triethyl phosphite with several substituted 2-bromoacrylates has been investigated. (Z)-2,3-Dibromopropenoate reacts with triethyl phosphite to give diethyl 2-bromo-2-(ethox-ycarbonyl)vinylphosphonate in 58% yield. This, on treatment with Et N in refluxing Et2O, produces 2-propynoate in 73% yield. Methyl 2-bromoacrylate reacts with triethyl phosphite to give diethyl 2-(methoxycarbonyl)vinylphosphonate in 68% yield, which, by hydrogenation in the presence of Raney-Ni, gives in almost quantitative yield 2-(methoxycarbonyl)ethylphosphonate. Alkyl... 

Another case where the formation of the phosphane arm is the result of a Cp methyl C.H activation process is the reaction of bis(trimethylsilyl)derivative 240, which is closely related to 232, with 2 equiv of methyl or ethyl propynoate. The two propynoate units are coupled, and the unusually complex structures 243 and 244 are formed (Scheme 45). 243 has been the subject of an X-ray crystallographic investigation. Although the authors do not specifically comment on the stereochemistry, the fact that both compounds show one singlet in the P NMR spectrum indicates that 243 and 244 are formed diaste-reoselectively, presumably via 241 and 242. 

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