Isochromenylium-4-ylplatinum(II) species, generated from 1-(2-alkynylphenyl)hex-5-en-1-ones and Pt(II), reacted with a pendant olefin via [3+2] cycloaddition to form tetracyclic Pt–carbene complexes, which underwent C–H insertion with a benzyloxy group at δ or ε positions to give highly complex polycycles, which are otherwise hard to access.