2-(3-Benzyloxy)prop-1-ynyl)benzaldehyde with PtCl2 in toluene would form Pt-pyryliums that underwent [3+2] cycloaddition with alkenes to the oxygen-bridged (5H-benzo[7]annulen-5-ylidene)platinum(II) intermediates with good stereoselectivities. Their tandem rearrangement afforded diverse types of polycycles depending on the electronic nature of the alkenes.
![Graphical abstract: Stereocontrolled synthesis of oxygen-bridged polycycles via intermolecular [3+2] cyclization of platinum-bound pyrylium with alkenes](http://hg.y866.cn/compound/lib/scimg/usr/1/C001495H.jpg)
