Metal-catalyzed regioselective oxy-functionalization of internal alkynes: an entry into ketones, acetals, and spiroketals.

[reaction: see text] Platinum(II) and an unusual cationic gold(I) complex were identified as mild catalysts for the room temperature cycloisomerization or tandem hydroalkoxylation/acetal formation of unactivated internal alkynols. Under the appropriate conditions, 5-endo, 5-exo, 6-endo, and 6-exo cycloisomerization modes are all available.