The (4 + 3) cycloaddition of 2-trialkylsilyl-4-alkylbutadienes with an N-methyloxidopyridinium ion affords cycloadducts with high regioselectivity and excellent endo selectivity.
p-Hydroxylphenylpyridylthiazole (HPPT) produces charge transfer induced fluorescence strongly influenced by metal ions. The Zn–HPPT-complex exhibits a Stokes emission of 137 nm (67 nm shift relative to neutral HPPT) with a quantum yield of 92%.
Easily prepared cycloadducts derived from the (4+3) cycloaddition of oxidopyridinium ions with dienes reacted intramolecularly in a [2+2] cycloaddition process to afford complex polycyclic species in which the tropane skeleton was embedded.
[EMBARGOED UNTIL 12/1/2023] The development of endo/exo selectivity of intermolecular (4+3) cycloaddition reactions of an N-methyl oxidopyridinium ion has been studied. Dienes that contain silyl groups, R-groups, and contain both silyl group and R-groups were investigated to compare the stereoselectivity of the intermolecular (4+3) reaction. The introduction of steric hindrance in the form of 2-trialkylsilyl-4-alkylbutadienes can enhance the endo selectivity of the intermolecular (4+3) reaction. The N-methyloxidopyridinium ion reacted with 2-trialkylsilyl-4-alkylbutadienes to afford cycloadducts with high regioselectivity and endo selectivity. The attempted cleavage of a trialkyl silyl of the (4+3) cycloadducts has led to a new discovery. N-Iodosuccinimide (NIS) was employed as the reagent and the hexafluoroisopropanol (HFIP) was employed as the solvent for the iododesilylation. However, functionalization of the cycloadducts at the bridgehead carbon was the only observed. An attempt to modify the functional group at the bridgehead carbon was unsuccessful. Based on the proposed mechanism and the product formation, HFIP acted as the nucleophile. An extension of the aforementioned study investigated the efficacy of the (4+3) cycloadducts as reactants in a [2+2] photocycloaddition reaction. Irradiation by a 450-watt Hanovia medium-pressure mercury lamp of the (4+3) cycloadducts can induce a [2+2] photocycloaddition reaction. The intramolecular [2+2] photocycloaddition reaction of (4+3) cycloadducts afford polycyclic compounds possession an embedded tropane skeleton in excellent yield.
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