Propargyl benzoate

The reaction of propargyl benzoate with 3,4-bis(azidomethyl)-l,2,5-oxadiazole 188 afforded bistriazole 189 (Equation 35) <2004RJ01156>. 

Nair, Nanarati, Nair, Kisliuk, Gaumont, Hsiao and Kalman have prepared the 5,8-dideazapteroic acid derivative (676), a useful precursor to polyglutamate analogues, from (228) and ethyl />-(jV-propargyl)benzoate, followed by saponification. Similarly, (232q) and (232r) were obtained from (228) and (231) R = 2-butynyl or cyclopropylmethyl) (Scheme 3.148) [275]. 

Umpolung of propargyl compounds occurs in the presence of excess Et2Zn, and homopropargyl alcohols 187 are obtained by the reaction of propargyl benzoates (186) with benzaldehyde, although the exact mechanism is not known. Ethylallene, which is expected to be formed by transmetallation of the allenylpalladium with Et2Zn and reductive elimination, is not formed [41],... 

Umpolung substitutions in which allylic or propargylic benzoates are converted into nucleophiles are realized in the presence of diethylzinc. 

Under carefully controlled conditions, the reaction proceeds with excellent stereocontrol. Addition of the allenylzinc reagent derived from the (i )-mesylate 101 to (i )-aldehyde 100 proceeded at -20 °C to give the anti-anti triad 102 in 70 % yield with a small amount of the anti-syn isomer [30], As an intramolecular version, the propargyl benzoate 103 attacked the methyl ketone to afford the cyclopentanol 104 using Et2Zn and an Lewis acid with high stereocontrol. The most effective Lewis acid was Yb(OTf)3. A good catalyst was Pd(OAc)2-P(n-Bu)3 [31]. 

The furan 123 was obtained by intramolecular reaction of the propargyl benzoate with an enolate of the f-keto ester in 122 using DPPF as a ligand, and the reaction was applied to the synthesis of the C(l)-C(18) segment of lophotoxin [38]. 

Treatment of the propargyl benzoate 162 with Pd2(dba)3 and DPPF in the presence of A -alkyltosylamide generated the allenylpalladium 163, and the TT-allylpalladium intermediate 164 was generated by the attack of the amino group. 

As in all C-C cross-coupling reactions, the Negishi reaction mechanism consists in three steps (Fig.4.1) oxidative addition, transmetalation, and reductive elimination. The former and the latter are common to all the other cross-coupling reactions, whereas the transmetalation step is particular of this reaction. Unfortunately, this transmetalation has been less studied compared to the ones in the Stille [12-17] or Suzuki reactions, [18-21] in spite of the fact that the transmetalation between organozinc and palladium complexes is also involved in other relevant processes, such as the hydroalkylation of styrenes, [22] the asymmetric allylation of aryl aldehydes, [23] the coupling propargylic benzoates and aldehydes, [24] or the double-transmetalation oxidative cross-coupling reaction [25, 26]. 

Exciton coupling is also observed in methacrylate derivatives of allylic alcohols151 and in a benzoate derivative of a homoallylic alcohol152. For benzoates of propargylic alcohols of S configuration 11 in which the O-Bz bond is assumed anti to the C-R1 bond, a Dc Voe calculation predicts a positive benzoate Cotton effect, in accordance with experimental153. 

Addition of lithium reagent derived from 355 to 382 produced a 1 1 mixture of adducts 363 in 75% yield. As this pro C-9 center will later be oxidized to the ketone, this mixture is of no consequence. LAH reduction of the propargyl alcohol followed by protection of the C-9 hydroxyl as the benzoate gave a 73% yield of the ( , )-diene 364. The primary and secondary alcohols, freed by cleavage of the acetonide, were protected as the trityl ether and benzoate, respectively, followed by desilylation to afford 365. The required two-carbon unit... 

Carbohydrate allenyl ethers have been prepared via the corresponding propargyl ethos,and sucrose 0-octadienyl ethers have been synthesized by a novel telomerisation of butadiene with sucrose in the presence of Pd(acac>2 and PhsP. Radical bromination of allyl ethers using MBS in CCU in the presence of isopropylidene acetals, acetates and benzoates has allowed the selective removal of the allyl ethers with a hydrolytic work-up. ... 

To a solution of benzoyl(tributyl)stannane (0.10 mmol) and propargyl 2-furoate (0.20 mmol) in dibutyl ether (0.15 mL) is added Pd/C (10 wt%, 0.2 mg), and the resulting mixture is stirred at 50 °C for 42 h before the mixture is filtered through a Florisil pad. Concentration of the filtrate in vacuo and purification of the residue by flash column chromatography (hexane-ethyl acetate = 10 1) on silica gel gives the title products in 77% yield. The success of this kind of reaction heavily depends on the sort of esters. Benzoate gives the same product in 44% aetatae, 29% 2-fiiroate 66% when 2.5 mol% of Pd2(dba)3 is used. Pd/C is the best catalyst. ... 

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