Methyl-3-pentenoate

Carbonyiation of butadiene gives two different products depending on the catalytic species. When PdCl is used in ethanol, ethyl 3-pentenoate (91) is obtained[87,88]. Further carbonyiation of 3-pentenoate catalyzed by cobalt carbonyl affords adipate 92[89], 3-Pentenoate is also obtained in the presence of acid. On the other hand, with catalysis by Pd(OAc)2 and Ph3P, methyl 3,8-nonadienoate (93) is obtained by dimerization-carbonylation[90,91]. The presence of chloride ion firmly attached to Pd makes the difference. The reaction is slow, and higher catalytic activity was observed by using Pd(OAc) , (/-Pr) ,P, and maleic anhydride[92]. Carbonyiation of isoprcne with either PdCi or Pd(OAc)2 and Ph,P gives only the 4-methyl-3-pentenoate 94[93]. 

Acetoxy-1,4- naphthoquinone [ 1,4-Naphthalenedione, 2-(aoetyloxy)-] 4-Methyl-3-pentenoic [3-Pentenoic acid, 4-methyl-] 2-Acetoxy-3-(y,y-dimethylallyl) [1,4 -Naphthalen ed i one, 2-(acetyloxy)-3-(3-methyl-2-butenyl)-] 73 4... 

The Co2(CO)g/pyridine system can catalyze carbomethoxylation of butadiene to methyl 3-pentenoate (Eq. 6.44) [80]. The reaction mechanism of the cobalt-catalyzed carbalkoxylation of olefins was investigated and the formation of a methoxycar-bonylcobalt species, MeOC(0)Co from a cobalt carbonyl complex with methanol as an intermediate is claimed [81, 82]. 

No dimerization-carbonylation takes place with isoprene, irrespective of the catalytic species (78). Selective formation of 4-methyl-3-pentenoate (75) was observed in alcohol by the catalysis of either PdCl2 or Pd(OAc)2 and PPh3 ... 

Chlorostannate ionic liquids have been used in hydroformylation reactions [23], Acidic [bmimjCl-SnCb and [l-butyl-4-methylpyridinium]Cl-SnCl2 were prepared from mixing the respective [cation]+ Cl with tin(II)chloride in a ratio of 100 104, much in the same way that the chloroaluminates are made (see Chapter 4). Both these chlorostannate ionic liquids melt below 25 °C. Addition of Pd(PPh3)2Cl2 to these chlorostannate ionic liquids leads to a reaction medium that catalyses the hydroformylation of alkenes such as methyl-3-pentenoate as shown in Scheme 8.9. The ionic liquid-palladium catalyst solution is more effective than the corresponding homogeneous dichloromethane-palladium catalyst solution. The product was readily separated from the ionic liquid by distillation under vacuum. This is an important reaction as it provides a clean route to adipic acid. 

When heated at 230 °C, tetrahydro-l,3-oxazines 173, bearing an a,/3-unsaturated ester substituent at position 2, underwent a retro-ene reaction and yielded 5,6-dihydro-477-l,3-oxazines 174 together with methyl 4-methyl-3-pentenoate 175 (Equation 16). For the methyl-substituted oxazine 173 (R = Me), the yields of both products were somewhat higher than those in the reaction of the unsubstituted analog 173 (R = H) <1997JHC501>. 

In an attempt to elaborate50 a synthetic access to DL-garosamine [126, 3-deoxy-4-C-methyl-3-(methylamino)-DL-arabinopyranose], the 1,5-lactone of 5-hydroxy-4-methyl-3-pentenoic acid (124) was oxy-aminated, to yield 2,3-dideoxy -C-methyl-3-p-toluenesulfonamido-DL-enyfhro-pentono-l,5-lactone (125). Introduction of a hydroxyl... 

Iodolactonization of /3,-y-unsaturated acids can also be achieved by the reaction of iodine with the thallium(I) carboxylates in ether solution. This reaction also has the possibility of giving /3- or -y-lactones, with the substitution on the double bond having the major influence. Thus thallium 3-butenoate gave the /3-lactone, while thallium 4-methyl-3-pentenoate gave the y-lactone, both in high yields (74JCS(Pl)l864). 

Both [Pd(OAc)2] and [Pd(acac)2] were used as catalyst precursors, in the presence of PPh3 or PBun3. No catalysis occurred here in absence of the phosphorus ligand. When isoprene was carbonylated using [Pd(OAc)2] and PPh3 as catalyst precursor, dimerization of the alkene did not take place, the ester of 4-methyl-3-pentenoic acid being formed as the only product.529... 

A wide variety of unsaturated carboxylic acids have been allowed to react with HBr.101 Carboxylic acids with remote C—C double bonds react as simple alkenes.138,139 4-Pentenoic acid reacts with HBr neat or in a polar solvent to give exclusively 4-bromopentanoic acid, but the reaction in nonpolar solvents affords only 5-bromopentanoic acid.136 On the other hand, 5-methyl-4-hexenoic acid produces only the S-bromo acid. A similar pattern is followed by 3-butenoic, 3-pentenoic and 4-methyl-3-pentenoic acids. No matter what the substitution pattern, 2-alkenoic acids always favor the 3-bromo acid.113,136,140,141 Addition of HBr to cyclic a,3-unsaturated acids initially forms predominantly the product of trans diaxial addition which upon longer reaction time or higher temperature isomerizes to the trans product (equation 92).57,141,142 Similar observations have been made on bicyclic a.fj-unsaturated acids.141... 

The metal carboxylate insertion mechanism has also been demonstrated in the dicobaltoctacarbonyl-catalyzed carbomethoxylation of butadiene to methyl 3-pentenoate.66,72 The reaction of independently synthesized cobalt-carboxylate complex (19) with butadiene (Scheme 8) produced ii3-cobalt complex (20) via the insertion reaction. Reaction of (20) with cobalt hydride gives the product. The pyridine-CO catalyst promotes the reaction of methanol with dicobalt octacarbonyl to give (19) and HCo(CO)4. 

The transformation of an alkene into an aldehyde by addition of CO and H2 (syngas) across an olefinic double bond represents one of the world s most important, homogeneously catalysed processes.11"51 Unwanted side-reactions include isomerisation and hydrogenation and, in the case of internal olefins, numerous products may arise as shown in Scheme 4.1 for methyl-3 -pentenoate. 

C4C,im]Cl-SnCl2 [C4ClPy]Cl-SnCl2 PtCl2(PPh3)2 + 4 PPh3 Methyl-3-pentenoate 31-37 1.3 [39]... 

Methyl 5-methoxy-3-oxopentanoate, 314 Methyl methylthiomethyl sulfoxide, 314 2-Methyl-5-nitroisoquinolinium iodide, 467 Methyl 2-nitrophcnyl disulfide, 314-315 2-Methyl-3-pentenoic acid, 65... 

Bromolactonizatiott. Corey and Hase have observed high stereoselectivity in halolactonization of an acylic /3,y-unsaturated acid. Thus reaction of bromine with the thallium salt of frans-2-methyl-3-pentenoic acid (1) with Btj in CH2CI2 at —78° results in one halolactone (2) in about 90% yield, even though two additional asymmetric centers are introduced. The reaction was also conducted with the resolved acid. 

The halocyclization of ( )-2-methyl-3-pentenoic acid occurs with high stereoselectivity under various conditions affording the y-iodo- and y-bromolactones20. (/ )-( )-2-Methyl-3-pentenoic acid (5), easily obtained by separation of the racemic acid with (R)- or (S)-a-methylbenzyl-amine, affords the (37 ,47 ,5,S )-y-lactone 6 susceptible to further transformation. The iodolac-tonc is obtained in 95% yield by reaction of the sodium salt of the unsaturated acid with iodine in methanol/water (85 15) containing sodium hydrogen carbonate at — 78 °C for 6 h. The IR spectrum confirms the presence of the y-lactone functionality while the H-NMR data is consistent with a trans,trans-arrangement21 of the substituents. The bromolactone can be obtained in 85-90% yield (mp 45-46°C) by treatment of the thallium salt of (E)-5 with bromine in dichloromethane at — 78 °C20. 

No isomerization of the double bond is reported in the conversion of 3-pentenonitrile to the olefinic ester, methyl 3-pentenoate, by hydrogen chloride ki methanol. ... 

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