Tin triflate promoted synthesis of bicyclic and tricyclic sulfonyl dihydropyrans

Tin triflate-promoted one-pot intramolecular annulation of α-geranyl or α-farnesyl β-ketosulfones 3–4 affords the respective bicyclic or tricyclic sulfonyl dihydropyrans 5–6 in moderate to good yields via a cascade cation-olefin-carbonyl carbocyclization process. The starting materials 3 and 4 were obtained by K2CO3-mediated α-geranylation or α-farnesylation of β-ketosulfones 1 with bromides 2a or 2b. The structures of the key products were confirmed by X-ray crystallography.

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