Abstract
The Diels–Alder cycloaddition between bisdienes and bisdienophile incorporating the 7-oxa-bicyclo[2.2.1]heptane unit are well known to show high diastereoselectivity that can be exploited for the synthesis of molecular belts. The related bisdiene 5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octene is a valuable building block for the synthesis of photoprecursors for acenes, but it has not been employed for the synthesis of molecular belts. The present work investigates by computational means the Diels–Alder reaction between these bisdiene building blocks with syn-1,4,5,8-tetrahydro-1,4:5,8-diepoxyanthracene, which shows that the diastereoselectivity of the Diels–Alder reaction of the etheno-bridged bisdiene is lower than that of the epoxy-bridged bisdiene. The reaction of the etheno-bridged bisdiene and syn-1,4,5,8-tetrahydro-1,4:5,8-diepoxyanthracene in 2:1 ratio yields two diastereomers that differ in the orientation of the oxa and etheno bridges based on NMR and X-ray crystallography. The all-syn diastereomer can be transformed into a molecular belt by inter- and intramolecular Diels–Alder reactions with a bifunctional building block. The molecular belt could function as a synthetic intermediate en route to a [11]cyclacene photoprecursor.
Highlights
The Diels–Alder (DA) reaction developed into a powerful synthetic method since its discovery more than 100 years ago [1,2,3,4,5,6]
We demonstrate that diastereomer 6a can be obtained from 1b and 2 (Scheme 1c) with sufficient diastereomeric excess to employ it in the synthesis of a molecular belt, as described in the second part of this paper
The Diels–Alder reaction between the bisdienes 1 and the bisdienophile 2 in a 1:1 ratio can result in four diastereomeric products 3a–d and 4a–d
Summary
The Diels–Alder (DA) reaction developed into a powerful synthetic method since its discovery more than 100 years ago [1,2,3,4,5,6]. As a member of the class of pericyclic reactions, this cycloaddition is valuable due to its stereospecificity and the often observed high diastereoselectivity. This last feature is highly desirable and turned out to be the key to the successful synthesis of molecular belts [7,8,9,10]. The DA reaction of a 1:1 mixture of 1a and 2 exclusively yields the syn/endo-H isomer 3a out of four possible diastereoisomers due to stereoelectronic effects, as discussed by Stoddart et al (Scheme 1b) [7]. We follow their nomenclature and use the descriptors syn and anti for the relative configurations of the endoxide bridges and exo and endo for the relative configurations of the hydrogen atoms of the bisdiene after DA reaction
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
