Butadiene reaction with methyl acrylate

BICYCLOPROPYLIDENE possesses unique reactivity toward a wide range of electrophiles and nucleophilic carbenes. (E)-I-DIMETH YLAMINO-3-tert-BUTYLDIMETHYL-SILOXY-1,3-BUTADIENE is a highly reactive diene for Diels-Alder reactions, as described in an accompanying procedure for the synthesis of 4-HYDROXYMETHYL-2-CYCLOHEXEN-1-ONE via the Diels-Alder reaction with methyl acrylate. Finally, this section concludes with the preparation of DIETHYL [(PHENYLSULFONYL)METHYL]PHOSPHONATE, a reagent that is very useful for synthesis of [Pg.285]

Diels-Alder Reactions. 2-Trimethylsilylmethyl-1,2-butadiene and 2-trimethylstannylmethyl-1,3-butadiene undergo facile cycloaddition with dienophiles (eq 11). The reactions of 2-trimethylsilylmethyl- and 2-trimethylstannylmethyl-1,3-butadiene with unsymmetrical dienophiles give the so-called para product predominantly, and the selectivity is much higher in the reactions with 2-trimethylsilylmethyl- and 2-trimethylstarmylmethyl-1,3-butadiene compared to reactions with isoprene. The paralmeta ratios in the reactions with methyl acrylate (eq 12) are 70/30 (X = H), 84/16 (X = SiMej), and 91/9 (X = SnMes)."... 

Further studies by Garcia, Mayoral et al. [10b] also included DFT calculations for the BF3-catalyzed reaction of acrolein with butadiene and it was found that the B3LYP transition state also gave the [4+2] cycloadduct, as happens for the MP2 calculations. The calculated activation energy for lowest transition-state energy was between 7.3 and 11.2 kcal mol depending on the basis set used. These values compare well with the activation enthalpies experimentally determined for the reaction of butadiene with methyl acrylate catalyzed by AIGI3 [4 a, 10]. 

Cycloaddition reactions of (E)-l-acetoxybutadiene (18a) and (E)-l-methoxy-butadiene (18b) with the acrylic and crotonic dienophiles 19 were studied under high pressure conditions [9] (Table 5.1). Whereas the reactions of 18a with acrylic dienophiles regioselectively and stereoselectively afforded only ortho-enJo-adducts 20 in fair to good yields, those with crotonic dienophiles did not work. Similar results were obtained in the reactions with diene 18b. The loss of reactivity of the crotonic dienophiles has been ascribed to the combination of steric and electronic effects due to the methyl group at the )S-carbon of the olefinic double bond. 

A systematic study of the effect of pressure and density on the regiochemical course of the Diels-Alder reactions of methyl acrylate and 2-substituted 1,3-butadienes carried out in SC-CO2 was recently reported [87]. The reactions were compared with those carried out in a conventional medium such as toluene. Some results are illustrated in Table 6.15. 

Table 6.15 Regioselectivity of Diels-Alder reactions of methyl acrylate with 2-substituted-l,3-butadienes in sc- CO2 and PhMe...

Butadiene with an electron donating group at the 2-position has the largest HOMO amplitude on C, (Scheme 15). A bond forms between Cj of the dienes and Cp of the dienophiles (Scheme 17b). This is in agreement with the exclusive formation of 1,4-disubstituted cyclohexene in the reaction of 2-ethoxybutadiene with methyl acrylate (Scheme 13b) [13, 14]. 

The reaction rates for the cycloaddition of several of the mentioned dienophiles to electron-rich dienes are significantly increased upon addition of a catalytic amount of a Lewis acid. The A1C13 complex of methyl acrylate reacts 100,000 times faster with butadiene than pure methyl acrylate (Figure 15.21). Apparently, the C=C double bond in the Lewis acid complex of an acceptor-substituted dienophile is connected to a stronger acceptor substituent than in the Lewis-acid-free analog. A better acceptor increases the dienophilicity of a dienophile in a manner similar to the effect several acceptors have in the series of Table 15.1. 

Methoxycarbonylcyclopropane derivatives are also obtained in 38% yield (cis.trans = 30 8) by the reaction of l-methylbicyclo[1.1.0]butane with methyl acrylate in the presence of a catalytic amount of [ RhCl(norbomadiene) 2], in addition to 2-methyl-1,3-butadiene (37%) and 2,7-dimethyl-l,4,7-octa-triene (25%). ... 

In 1987, Hill and co-workers (75) reported a clever synthesis of the pentacyclic cephalotaxine analog 246 starting from the nitrostyrene derivative 98 (Scheme 42). The Diels-Alder adduct 244, obtained by the reaction of butadiene sulfone with 98, was treated with methyl acrylate to give a single stereoisomer of the nitro ester, which was reduced with zinc in etha-nolic HCl to yield the lactam 245 and further reduced by Red-AI to the corresponding pyrrolidine. Pictet-Spengler cyclization with formaldehyde gave the pentacyclic amine 246. Alternatively, the reduced pyrrolidine obtained from 245 could be formylated, cyclized to the iminium salt by a Bischler-Napieralski protocol, and finally reduced with sodium borohy-dride to 246. Nearly identical sequences have also been reported by Bryce... 

In a subsequent study, Inukai and Kojima determined that the enthalpy of activation in the thermal reaction of butadiene with methyl acrylate was 18.0 ... 

Fig. 10.7. Computed transition structures for uncatalyzed and BF3-catalyzed Diels-Alder reaction of 1,3-butadiene with methyl acrylate. Reproduced from Tetrahedron, 53, 6057 (1997), by permission of Elsevier.

Selectivity is predicted by examination of the orbital coefficients of the HOMO and LUMO for both diene and alkene. The transition state for a typical reaction is shown for the reaction of methyl acrylate and 2-phenyl-1,3-butadiene (see 67), where the orbitals with largest coefficients (HOMOdiene-LUMOalkene) combine (the absolute value of the orbital coefficient is used, -0.625 0.69l and -0.475 1-0.471)) to predict the cycloadduct produced in the greatest amount (the para product, 68). Just as the HOMOgy-LUMOaikene is [0 - (-8.77) = 8.77], and it predicts the relative reactivity of these reactants. The magnitude of the orbital coefficients in each partner is important for predicting selectivity. In this case, the orbital coefficients are 0.065 and 0.004, respectively, and there is selectivity for the para product. Similarly, the orbital coefficients for 1-methoxy-1,3-butadiene and acrolein correctly predict the major product is the ortho adduct. For simple cases, the orbital coefficients can be estimated by a simple Hiickel molecular orbital calculation (a very low level calculation but one that gives a first approximation that is useful for estimating relative differences). 

Diels-Alder reactions. This diene is not very reactive in cycloadditions, even under BFs catalysis, and is less reactive than butadiene itself. In addition the regioselectively is slight. Thus it reacts with methyl acrylate to give both the ortho adduct (2) and the meta adduct (3) (equation I). A single adduct is... 

In a separate study, the MIT group investigated the Diels-Alder reaction of methyl acrylate with 2-f-butyl-1,3-butadiene, assuming that the ratio of isomers produced from this diene in scCOj would be more sensitive to reaction conditions if steric interactions were important (7). Little variation in regioselectivity was observed relative to normal Diels-Alder synthesis. 

Another aspect of the Diels-Alder reaction that can be rationalized with FMO theory is the regiochemistry observed with unsymmetric dienes or alkenes. Equation 11.45 shows the product distribution from the cycloaddition of 2-phenyl-l,3-butadiene (97) and methyl acrylate (98). The para" product 99 (named by analogy with aromatic compounds) is the major product, but some "meta" product (100) is produced as well. ... 

An ab initio MO computational study of the Diels-Alder addition of ethylene to butadiene reveals a symmetrical transition state and a concerted reaction profile. Extended Htickel MO calculations on the endo.exo product distribution in [4 + 2] reactions of cyclopentadiene indicate, within the range of intermolecular distances investigated, that the ewdo-orientation is energetically favoured. A study of the relationship between isomer distribution and solvent polarity in the reactions of cyclopentadiene with acrylonitrile and with methyl acrylate reveals that the endo-adduct. dicyclopentadiene and exo-adduct rdicyclopentadiene ratios are increased linearly with the empirical solvent polarity factor The favoured endo-... 

Draw the product formed by the Diels-Alder reaction of 2,3-diphenyl-1,3-butadiene with methyl acrylate. 

Such copolymers of oxygen have been prepared from styrene, a-methylstyrene, indene, ketenes, butadiene, isoprene, l,l-diphen5iethylene, methyl methacrjiate, methyl acrylate, acrylonitrile, and vinyl chloride (44,66,109). 1,3-Dienes, such as butadiene, yield randomly distributed 1,2- and 1,4-copolymers. Oxygen pressure and olefin stmcture are important factors in these reactions for example, other products, eg, carbonyl compounds, epoxides, etc, can form at low oxygen pressures. Polymers possessing dialkyl peroxide moieties in the polymer backbone have also been prepared by base-catalyzed condensations of di(hydroxy-/ f2 -alkyl) peroxides with dibasic acid chlorides or bis(chloroformates) (110). 

In Illustrations 8.3 and 8.6 we considered the reactor size requirements for the Diels-Alder reaction between 1,4-butadiene and methyl acrylate. For the conditions cited the reaction may be considered as a pseudo first-order reaction with 8a = 0. At a fraction conversion of 0.40 the required PFR volume was 33.5 m1 2 3, while the required CSTR volume was 43.7 m3. The ratio of these volumes is 1.30. From Figure 8.8 the ratio is seen to be identical with this value. Thus this figure or equation 8.3.14 can be used in solving a number of problems involving the... 

---