Methyl propargyl carbonate

Among several propargylic derivatives, the propargylic carbonates 3 were found to be the most reactive and they have been used most extensively because of their high reactivity[2,2a]. The allenylpalladium methoxide 4, formed as an intermediate in catalytic reactions of the methyl propargylic carbonate 3, undergoes two types of transformations. One is substitution of cr-bonded Pd. which proceeds by either insertion or transmetallation. The insertion of an alkene, for example, into the Pd—C cr-bond and elimination of/i-hydrogen affords the allenyl compound 5 (1.2,4-triene). Alkene and CO insertions are typical. The substitution of Pd methoxide with hard carbon nucleophiles or terminal alkynes in the presence of Cul takes place via transmetallation to yield the allenyl compound 6. By these reactions, various allenyl derivatives can be prepared. 

The alka-l,2,4-trienes (ailenylaikenes) 12 are prepared by the reaction of methyl propargyl carbonates with alkenes. Alkene insertion takes place into the Pd—C bond of the ailenyipailadium methoxide 4 as an intermediate and subsequent elimination of/3-hydrogen affords the 1,2,4-triene 12. The reaction proceeds rapidly under mild conditions in the presence of KBr. No reaction takes place in the absence of an alkali metal salt[4j. 

Organoboranes react with propargylic carbonates. Usually, addition of a base is indispensable for Pd-catalysed reactions of organoboranes with aryl, alkenyl and allyl halides. However, the reaction of organoboranes with methyl propargyl carbonates proceeds without addition of the base, because methoxide as the base is generated in situ from the carbonates. For example, the 1,2,4-alkatriene 127 is obtained by the reaction of alkenylboranes 126 with propargylic carbonate 125 under neutral conditions [32],... 

Organoboranes react with propargylic carbonates. Usually, addition of a base is indispensable for the palladium-catalyzed reactions of organoboranes with aryl, alkenyl, and allyl halides. But the reaction of organoboranes with methyl propargyl carbonates proceeds... 

Furthermore, in 1998 Ube Industries, Ltd. expanded their research from doublebond compounds to triple-bond compounds and discovered that alkyne compounds such as methyl propargyl carbonate (13), propargyl acetate (14), and 2-butyne-l,4-diol dimethyl dicarbonate (15) suppress the decomposition of PC [53]. In 1999, the same company discovered that a mixture of methyl propargyl carbonate (13) and VC is capable of improving battery performance even further [27, 54]. 

Unsubstituted methyl acetoacetate, bearing two active hydrogens, behaves differently. It reacts with methyl propargylic carbonate in a 1 1 ratio in THF at room temperature, giving an entirely different product (Scheme 25). In this case, at first C-alkylation of the central sp carbon of the allenylpalladium generates the 7r-allylpalladium intermediate bearing the... 

Carbonylation of propargylic carbonates proceeds under mild neutral conditions (50 °C, I-10 atm) using Pd(OAc)2 and Ph ,P as a catalyst, yielding the 2,3-alkadienoates 18 in good yields[9,10]. The 2.3-alkadienoates isomerize to 2,4-dienoates during the reaction depending on the solvents and reaction time. 2-Decynyl methyl carbonate is converted into methyl 2-heptyl-2,3-butadienoate (19) in 82% yield. 

Whereas triethyl (l-methyl-2-yl)indolyl borate (119) undergoes Pd-catalyzed coupling with propargyl carbonates in an 8 2 manner yielding 2-allenylindoles <96H(43)1591>, conducting this reaction in the presence of CO (10 atm) affords cyclopenta[fe]indoles 120 <96CC2409>. 

In 1985, Tsuji s group carried out a Pd-catalyzed reaction of propargyl carbonate with methyl acetoacetate as a soft carbonucleophile under neutral conditions to afford 4,5-dihydrofuran 109 [89-91]. The resulting unstable 109 readily isomerized to furan 110 under acidic conditions. In addition, they also reported formation of disubstituted furan 112 via a Pd-catalyzed heteroannulation of hydroxy propargylic carbonate 111 [92], Presumably, an allenylpalladium complex (c/. 114) was the key intermediate. 

Carbonylation of propargyl carbonates bearing an amino group yields lactams. The a-vinylidene /1-lactams 82 are prepared by the carbonylation of 4-benzylamino-2-alkynyl methyl carbonates 81 [20], The best results are obtained by using the cyclic phosphite (4-ethyl-2,6,7-trioxa-l-phosphabicyclo[2,2,2]octane) (83). The lactam formation is carried out in THF or MeCN as solvents at 50 °C under 1-10 atm of CO. 

Methyl-2-propynyl carbonate (176) reacted with 2 mol of malonate 177 to give 2,3-disubstituted propenes 181 and 182 under neutral conditions in boiling THF (Scheme 11-48). The carbanion 177 attacks the central sp-carbon of the allenylpalladium to generate 178, which picks up a proton from malonate to form the jr-allylpalladium intermediate 180. The intermediate 178 can be considered as a palladium carbene complex (179). The malonate anion attacks the 7r-allylpaUadium 180 as expected, to give 181. Migration of the double bond in 181 affords 182 [43,44]. Thus the propargylic carbonate 176 has two... 

Propargylic carbonates are converted to substituted allenyllithium species but I -alkynylsilanols undergo dilithiation (with r-BuLi-HMPA) and the subsequent reaction with electrophiles at the propargylic position. The doubly lithiated A-methyl aminals can be used in the preparation of Si-N- and P-N-containing heterocycles. ... 

In 1985, Tsuji s group carried out a Pd-catalyzed reaction of propargyl carbonate with methyl acetoacetate as a soft carbonucleophile under neutral conditions to afford... 

Dien-4-ynes 136 (R -R = alkyl) are produced from propargylic carbonates 135 and terminal alkynes in the presence of a palladium-phosphine complex and copper(I) iodide. The linear co-dimerization of terminal acetylenes and 1,3-dienes is catalyzed by ruthenium(cyclooctadiene)(cyclooctatriene)(trialkylphosphine) (alkyl = Et, Bu or octyl) thus 1-hexyne and methyl penta-2,4-dienoate give a mixture of the eneynes 137 and 138. Coupling of octa-l,7-diyne (139) with the acetylenic bromo acid 140 in aqueous THF-methanol containing butylamine, hydroxylamine hydrochloride and copper(I) chloride gave a mixture of the triynyl acids 141 and 142. ... 

In contrast to facile Pd(0)-catalyzed reactions of allyl esters with soft carbon nucleophiles via r-allylpalladium intermediate, propargyl esters such as acetate are less reactive toward soft carbon nucleophiles. However, /3-keto esters and malonates react under neutral conditions with propargyl carbonates using DPPE as a ligand [37], Acetoacetate reacts with meAyl propargyl carbonate (119) in THF at room temperature to afford 4-(methoxycarbonyl)-5-methyl-3-methylene-2,3-dihydrofuran (120) in 88 % yield. The furan 121 was obtained by isomerization of the methylenefuran 120 under slightly acidic conditions. 

---