Efficient synthesis of functionalised ten-membered lactones via acid-catalysed intramolecular reactions of 5-(tetrahydro 2-furyl)pentanoic trifluoroacetic anhydride

5-(Tetrahydro-2-furyl)pentanoic trifluoroacetic anhydride reacts in the presence of trifluoroacetic acid to yield 6-trifluoroacetoxy-9-nonanolide together with (E)-non-5-en-9-olide; treatment of the same mixed anhydride with titanium(IV) chloride gives 6-chloro-9-nonanolide, and its reaction with trifluoroacetic acid in the presence of sodium iodide leads to 6-iodo-9-nonanolide.