A Ring ExpansionStereoselective Cycloaddition of Carbohydrate-Derived Donor–Acceptor Cyclopropanes: Synthesis of Bridged Oxepanone–Indole Hybrids

An efficient method for the construction of sugar-derived
chiral
oxepanone–indole molecular hybrids is investigated. The reaction
condition is optimized by monitoring the progress at various temperatures,
with various solvents, and with different Lewis acid catalysts. Under
optimized conditions, high stereoselectivity and efficiency are achieved
in most of the formed cycloadducts. The accessibility of the strategy
is evaluated by utilizing an array of carbohydrate-derived donor–acceptor
cyclopropanes and variably substituted indole substrates. Additionally,
quick access to the bridged indole–oxepanone framework is described
by utilizing a diastereoselective (3+2) cycloaddition of aryl-substituted
donor–acceptor cyclopropanes incorporated in a pyran ring.