The 1:1 and 2:1 adducts of cyclopentadiene with p-benzoquinone

Abstract

This paper is dedicated to Professor Ross Stewart on the occasion of his 65th birthday PETER YATES and KRZYSZTOF SWITLAK. Can. J. Chem. 68, 1894Chem. 68, (1990.The exo-cis isomer (8) of the well-known endo-cis 1: 1 adduct (4) of cyclopentadiene andp-benzoquinone has been obtained by heating the endo-cis-anti-cis-endo 2: 1 adduct (13) withp-benzoquinone and also by heating 4 alone. The exo-cis isomer of the 1 : 1 adduct (11) of cyclopentadiene and p-toluquinone has also been obtained for the first time. Heating of the 2: 1 adduct 13 gives a mixture containing the endo-anti-e.ro isomer 15, the exo-anti-e.ro isomer 16, and 13. The structures of these two new isomers are assigned on the basis of (i) spectroscopic comparison with 13 and the known endo-syn-endo and endo-syn-exo isomers, 12 and 14; (ii) spectroscopic comparison of the corresponding tetrahydro compounds; and (iii) the conversion of tetrahydro 15 by oxidation and acetylation to the syrz-hydroquinone diacetate 28, which is stereoisomeric with the anti-hydroquinone diacetate 25, prepared by similar treatment of tetrahydro 13, 14, and 16. It is proposed that interconversion of the 1:l adducts occurs via dissociation-recombination, interconversion of the tetrahydro 2: 1 adducts occurs via enolization, while interconversion of the 2:l adducts themselves can occur by both routes.

Revisiting the stability of endo/exo Diels-Alder adducts between cyclopentadiene and 1,4-benzoquinone

“…The results discussed in the present paper can be used for a correct explanation of the experimental results obtained by Yates and Switlak 48 for thermal stereoisomerization of adduct endo 3. In their study, 48 the authors reflux a solution of adduct endo in toluene under argon for 36 h and the products of this thermal isomerization consisted of 1:9 mixture of adduct exo and endo (50%), one hydroquinone derivative (1,4-dihydro-1,4-methanonaphthalene-5,8-diol) and 1,4-benzoquinone.…”

“…In their study, 48 the authors reflux a solution of adduct endo in toluene under argon for 36 h and the products of this thermal isomerization consisted of 1:9 mixture of adduct exo and endo (50%), one hydroquinone derivative (1,4-dihydro-1,4-methanonaphthalene-5,8-diol) and 1,4-benzoquinone. The authors suggest that the small amount of exo adduct is due to the position equilibrium was not established under that conditions.…”

“…One of the most used examples of the Diels-Alder reaction, which is listed in several Organic Chemistry textbooks, [36][37][38] is that between cyclopentadiene (1) and maleic anhydride which, at room temperature, gives only the endo adduct that is then converted at 200 o C to the thermodynamically more stable exo adduct through a retro Diels-Alder reaction. 4 According to several authors, [39][40][41][42][43][44][45][46][47][48][49][50][51][52] the Diels-Alder reaction between cyclopentadiene (1) and 1,4-benzoquinone (2) (Scheme 1), gives, in a similar way, only the kinetic endo adduct 3, although the exo adduct 4 has higher stability than the endo adduct 3 due to the steric repulsive interaction present in the endo form. Actually, we observed from the 1 H NMR spectrum of the reactional mixture, 98% of compound 3 and 2% of compound 4 (Fig.…”

“…4b) is more stable (thermodynamic product) than exo, which is in disagreement with literature data. [39][40][41][42][43][44][45][46][47][48] It is reported in literature [39][40][41][42][43][44][45][46][47][48] that exo is the thermodynamic and endo is the kinetic product.Theoretical calculations at high level of theory (Table 1) were performed for adducts endo and exo to get more accurate energies values to check if the endo adduct is in fact the thermodynamic product. It can be seen from Table 1 that in all levels of theory applied in the present study, the endo adduct is the more stable than exo.…”

Use of different microporous and mesoporous materials as catalyst in the Diels–Alder and retro-Diels–Alder reaction between cyclopentadiene and p-benzoquinoneActivity of Al-, Ti- and Sn-doped silica

“…Identification of these products was carried out by NMR techniques ( 1 H, 13 C, DEPT, COSY, HETCOR and NOE) being spectral data fully coincident with literature [22].…”