Mercury triflate cyclization with

Thio- and selenoacetals and esters are excellent substrates for mild Friedel-Crafts reactions, because of the affinity of sulfur and selenium for copper (Sch. 23). Anisole was readily acylated with methylselenoesters 94 at room temperature with activation by CuOTf to affordpnra-substituted (> 95 %) derivatives 95 [50,51]. Mercury(II) and copper(II) salts, which were effective for the activation of selenyl esters for reaction with alcohols, amines, and water, were not effective for the Friedel-Crafts reaction. Aromatic heterocycles 96 could be acylated in high yields, and the alkylation product 100 was obtained from dibutylthioacetal 99 and anisole. Vedejs has utilized this methodology in the cyclization of 101 to afford 102 in 77 % yield [52]. This intramolecular variant did not require the use of the more reactive bis copper triflate-benzene complex. 

Portella also reported the formation of non-hydroxy-containing 1,4- and l,5-bis(acylsilanes). For example, treatment of 2-TMS-1,3-dithiane with n-butyllithium followed by exposure to a variety of l,2-bis(triflates) provided symmetric and unsymmet-ric 1,4-bisdithianes in modest to good yield. Treatment with mercury salts or Mel revealed the bis(acylsilane), which upon exposure to PTSA cyclized to afford the corresponding 2,5-bis-trimethylsilylfuran (eq 32). 

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