Modular Assembly of Furotropones and Benzofurotropones, and Study of Their Physicochemical Properties

A rapid
and straightforward synthesis of a novel series of furo­[2,3-d]­tropones (or cyclohepta­[b]­furan-6-ones)
has been developed starting from readily and commercially available
materials. Directed α-lithiation of furan-3-carboxaldehydes
and subsequent reaction with a variety of aldehydes efficiently provide,
in one step, access to 3-formyl-2-furylcarbinols, which are otherwise
only accessible with difficulty. The 3-formyl-2-furylcarbinols are
further elaborated in two steps to the synthesis of furo­[2,3-d]­tropones in good yields via sequential bismuth­(III)­chloride-catalyzed
furfurylation and an unusual base promoted cyclization strategy. Thus,
diverse polysubstituted furotropones and benzofurotropones can be
rapidly assembled. This methodology thereby offers a potential approach
for the synthesis of several bioactive natural products containing
cyclohepta­[b]­furan core and also for the buildup
of complex molecular architectures through higher order cycloaddition
reactions of tropones. Further, the new chromophores have been found
to possess promising fluorescence properties. Selective fluorogenic
sensing behavior of furotropones toward Fe3+ ions has also
been elucidated.