Short Access to Belt Compounds with Spatially Close CC Bonds and Their Transannular Reactions

Abstract

Two domino Diels-Alder adducts were obtained from 3,7-bis(cyclopenta-2,4-dien-1-ylidene)-cis-bicyclo[3.3.0]octane and dimethyl acetylenedicarboxylate or N-methylmaleimide under microwave irradiation. From the first adduct, a C20H24 diene with C2v symmetry was obtained by Zn/AcOH reduction, hydrolysis, oxidative decarboxylation, and selective hydrogenation. Photochemical [2+2] cycloaddition of this diene gave a thermally unstable cyclobutane derivative, which reverts to the diene. However, both the diene and the cyclobutane derivatives could be identified by X-ray diffraction analysis upon irradiation of the diene crystal. New six-membered rings are formed upon the transannular addition of bromine or iodine to the diene. The N-type selectivity of the addition was examined by theoretical calculations, which revealed the distinct susceptibility of the doubly bonded carbon atoms to the bromine attack.

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

“…121,122 In their work on the synthesis of pagodans and isopagodans, the Prinzbach group applied similar conditions to bridged dienes resulting in intramolecular [2 + 2] photocycloaddition reactions. 123 Further applications of photocycloaddition by direct excitation can be found in the field of belt compounds 124 and in cyclophane chemistry. 125 Sensitization of the photocycloaddition substrate is applicable if the triplet energy of the olefin is lower than the triplet energy of the sensitizer.…”

“…Gleiter and Brand employed the intramolecular [2 + 2] photocycloaddition for the synthesis of octamethylcubane and related products by direct irradiation. , In their work on the synthesis of pagodans and isopagodans, the Prinzbach group applied similar conditions to bridged dienes resulting in intramolecular [2 + 2] photocycloaddition reactions . Further applications of photocycloaddition by direct excitation can be found in the field of belt compounds and in cyclophane chemistry …”