Structure of the 1:1 Cycloadduct Formed via Thermal Reaction of Cyclopentadiene with Hexacyclo [10.2.1.02,11.04,9.04,14.09,13]pentadeca-5,7-diene-3,10-dione

On the Origins of Diastereofacial Selectivity in Diels-Alder Cycloadditions

“…In both of these reactions, the ring-opened triene, 27 functions as a p-facially differentiated dienophile. 65 The Diels-Alder reaction that affords 28 as the exclusive 1:1 [4 + 2] cycloadduct has been investigated computationally by addressing two separate questions specifically: (i) What is the direction of electrocyclic ring-opening of 15a (i.e., consider formation of 29 vs. 30? (ii) What is the most energetically favored transition state among the various possible modes of Diels-Alder cycloaddition of cyclopentadiene to the preferentially-formed ring-opened triene?…”

“…22 kcal/mol relative to the corresponding transition structure for electrocyclic ring-opening of 15a to 29. 65 Next, two possible modes of Diels-Alder cycloaddition of cyclopentadiene to 29 were considered explicitly (i.e., [4 + 2] cycloadditions that lead to the formation of either 31 or 32). The transition structure of each cycloaddition was located by using restricted Hartree-Fock (RHF) theory and by assuming a concerted reaction mechanism.…”

“…In each case, a single [4 + 2] cycloadduct was formed; the products of these reactions were shown unequivocally to possess structures 34a and 34b, respectively via application of X-ray crystallographic methods. In view of the fact that electrocyclic ring-opening of 15a to 29 has been shown previously to occur at (or possibly below) 85 °C 49,64,65 it is particularly significant to note that in neither reaction of 15a with 33a or with 33b is any product formed that results via [4 + 2] cycloaddition of the diene to a C=C double bond in the tautomeric ring-opened triene (i.e., 28). 66 The energetics of the relevant Diels-Alder reaction of 15a with 33a have been investigated computationally.…”

Face Selection in Addition and Elimination in Sterically Unbiased Systems

“…The hexacyclic structure 123 and its reaction with more than twenty dienophiles has been studied by Coxon, Pandey, and Marchand …”

“…The hexacyclic structure 123 and its reaction with more than twenty dienophiles has been studied by Coxon, 159 Pandey, 160 and Marchand. 161 In most cases, the cycloaddition occurred exclusively at the "carbonyl face" to give adducts such as 124. In a few instances, mixtures were obtained, and in one, with diethyl azodicarboxylate, cycloaddition took place exclusively syn to the cyclobutane ring to give product 125 (with the nitrogen atoms pyramidal and in s-trans conformation).…”