Butyl acrylate, Diels-Alder with

Another tartaric acid-derived complex catalyzes the Diels-Alder reaction of terf-butyl acrylate and cyclopentadiene with good levels of enantiomeric excess (Scheme 42) [120]. The use of a smaller ester substituent resulted in lower enan-tioselectivity for the derived cycloadduct. 

The Diels-Alder reactions of the methyl or ethyl ester of benzenesulfonylindole-2-acrylic acid with several l-alkoxycarbonyl-l,2-dihydropyridines are reported and only a single stereoisomer was obtained, as in the case of l-methoxy(ethoxy)-carbonyl-1,2-dihydropyridines. However, when the Diels-Alder reaction of 17 was carried out with 8g[R = (CHsjsC], a mixture of two stereoisomers 18gand25were obtained in a 1 1 ratio (65% total yield). The bulky rerr-butyl group creates sufficient steric interference with the indole ring to cause the loss of stereochemistry ... 

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. 

A recent report [90] investigated the Diels-Alder reaction of cyclopentadiene with various acrylates in SC-CO2 catalyzed by Sc(OTf)j. The results relative to n-butyl acrylate, in SC-CO2 and in conventional solvents, are reported in Scheme 6.34. The catalyzed reaction carried out under supercritical conditions went to completion within 15 h at 50 °C, whereas the uncatalyzed reaction proceeded only to 10 % after 24 h. An increase of endo/exo diastereoselectivity was also observed. 

Scott Oakes et al. (1999a, b) have shown how adoption of SC conditions can lead to a dramatic pressure-dependent enhancement of diastereoselectivity. In the case of sulphoxidation of cysteine derivatives with rert-butyl hydroperoxide, with cationic ion-exchange resin Amberlyst-15 as a catalyst, 95% de was realized at 40 °C and with SC CO2. By contrast, with conventional solvents no distereoselectivity was observed. Another example is the Diels-Alder reaction of acrylates with cyclopentadiene in SC CO2 at 50 °C, with scandium tris (trifluoromethanesulphonate) as a Lewis acid catalyst. The endoiexo ratio of the product was as high as 24 1, while in a solvent like toluene it was only 10 1. 

R)- and (S)-f-Butyl-5-methylene-l,3-dioxolan-4-one, a Chiral a-Alkoxy Acrylate. It is also possible to introduce an ex-ocyclic double bond onto the dioxolanone ring, as in compounds (9)-(ll), derived from lactic and malic - acids. These a,3-unsaturated carbonyl derivatives are acceptors for radical additions and undergo cycloadditions with dienes and heterodienes. The Diels-Alder adduct (12) of ent-(9) with cyclopentadiene is formed with exo selectivity (96 4) and serves as aprecursor to norbomenone (13). Cycloadduct (14), obtained from methylenedioxolanone (9) and an open-chain triene, is also the result of an exo addition and is used in tetronolide synthesis. ... 

Supercritical carbon dioxide (SC-CO2) is an environmentally benign solvent that is providing a viable alternative to the traditional organic solvents. A Diels-Alder reaction between n-butyl acrylate and cyclopentadiene was investigated with the Lewis acid catalyst scandium tris (trifluoromethanesuffonate), primarily due to its solubility in SC-CO2 (Eq. 10-12) ... 

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. 

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