Methyl acrylate, Diels-Alder cycloaddition

Figure 3.5-2 Diels-Alder cycloaddition between cyclopentadiene and methyl acrylate.

The pioneer work on this subject using simple 1-azadienes is due to Ghosez et al. (82TL3261 85JHC69) they succeeded in reacting 1-azadienes as 47r-electron components in Diels-Alder cycloadditions. Thus, l-dimethylamino-3-methyl-l-azabuta-l,3-diene (a,/3-unsaturated hydrazone) 54 did undergo [4 + 2] cycloaddition to typical electron-poor dienophiles, e.g., methyl acrylate, dimethyl fumarate, acrylonitrile, maleic anhydride, and naphthoquinone, producing pyridine derivatives 55-57 (Scheme 14). 

The simple homochiral adduct from Diels-Alder cycloaddition of (/ )-pantolactone acrylate ester with cyclopentaidiene was hydrolyzed and converted to the methyl ketone in 89% yield through addition of 3... 

Scheme 7.1 The Diels-Alder cycloaddition offuran with methyl acrylate.

Clays [2] and zeolites [3] have been reported as good catalysts for Diels-Alder synthesis. Recently, we have studied the Diels-Alder cycloaddition between methyl acrylate (1) and cyclopentadiene (2) (Figure 1) and have shown that the solvent [4], the calcination of the solid [5] and the exchanged cation [6] play a decisive role. We now report the results obtained from the reactions of cyclopentadiene with methyl and (-)-menthyl acrylates, catalysed by K10 montmorillonites exchanged with different cations and dried at 120°C or calcined at 550°C. 

Diels-Alder cycloadditions have greater synthetic flexibility when suitable substituents on the diene are available for elaboration to functionality which is otherwise difficult to build into the structure. To this end, several schemes to novel 1,3-dienes have been described this year. Hagemann s ester (79) is a useful intermediate in synthesis of terpenoids. The ester is now conveniently available by regioselective Diels-Alder reaction of 1-methyl-l,3-bis(trimethylsiloxy)buta-1,3-diene (80) with ethyl acrylate. The yield is 61% overall after 5 days heating in xylene at 170—180 C, followed by hydrolysis of the moisture-sensitive adduct (81). The diene (80) is readily prepared from acetylacetone and trimethylsilyl chloride in the presence of triethylamine-zinc chloride in an ether-benzene mixture. The related diene (82), similarly prepared from 2-formylbutan-3-one, is used to give the useful cyclic dienophile (83). These sequences are outlined in Scheme 18. ... 

In all of these examples, the reaction products are under kinetic control. That is, the product mixture is determined by which product is made fastest rather than which is thermodynamically most stable. The Diels-Alder cycloaddition reaction gives another example of this phenomenon. The reaction of methyl acrylate with cyclopentadiene gives a mixture of two endo and exo products (see Scheme 2.5). 

The Diels-Alder cycloaddition reaction is a concerted reaction, with no change in the charge density upon going from reactants to the activated complex and finally to the products. Therefore, from the Hughes-Ingold approach, litde solvent effect is expected upon these reactions. In spite of this, dramatic solvent effects are often observed when a non-symmetric dienophile is used, and a mixture of products is formed. For instance, the reaction of methyl acrylate with cyclopentadiene gives a mixture of two products (see Scheme 10.61. 

The first step in a one-pot formation of a phenanthrene ring system from an enantiomericaUy pure rhenium-bound naphthalene is a TBDMS triflate-promoted Michael addition to 3-penten-2-one (eq 26). Electron-rich rhenium-bound naphthalenes also undergo TBDMS triflate-promoted conjugate addition reactions to less-activated Michael acceptors such as methyl acrylate, leading to the formal Diels-Alder cycloaddition product of naphthalene with this dienophile. ... 

Enamines have been observed to act both as dienophiles (46-48) and dienes (47,49) (dienamines in this case) in one-step, Diels-Alder type of 1,4 cycloadditions with acrylate esters and their vinylogs. This is illustrated by the reaction between l-(N-pyrrolidino)cyclohexene (34) and methyl t/-a i-2,4-pentadienoate (35), where the enamine acts as the dienophile to give the adduct 36 (47). In a competitive type of reaction, however, the... 

Evans s bis(oxazolinyl)pyridine (pybox) complex 17, which is effective for the Diels-Alder reaction of a-bromoacrolein and methacrolein (Section 2.1), is also a suitable catalyst for the Diels-Alder reaction of acrylate dienophiles [23] (Scheme 1.33). In the presence of 5 mol% of the Cu((l )-pybox)(SbF5)2 catalyst with a benzyl substituent, tert-butyl acrylate reacts with cyclopentadiene to give the adduct in good optical purity (92% ee). Methyl acrylate and phenyl acrylate underwent cycloadditions with lower selectivities. 

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