Self-activated supramolecular reactions: effects of host-guest recognition on the kinetics of the Diels-Alder reaction of open-chain oligoether quinones with cyclopentadiene.

摘要: Diels−Alder reactions of acyclic oligoether-substituted quinones 1b, 1c, 2b, and 2c with cyclopentadiene were accelerated by the addition alkali alkaline earth metal perchlorates, scandium trifluoromethane sulfonate (kc/kf = 1.2−23 for univalent cations, 11−1160 divalent 1700−192 000 Sc3+, where kcand kf are rate constants complexed uncomplexed quinones, respectively). The shorter-armed 1a, 2a, 3, however, exhibited no such acceleration effects. accelerations can be rationalized FMO consequence in which bound guest cation withdraws electron density from quinone dienophile lowers LUMO energy suitable orbital interaction HOMO cyclopentadiene. Despite poor selectivity, these oligoether showed larger than relevant quinocrown ethers 4 1.3−3.0 5.0−160 100−2020 Sc3+). effective wi...