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Whiskey Lactone is found as its cis- and trans-isomers in whiskey and in oakwood volatiles; the cis-isomer is the more important in sensory terms. It is a clear, almost colorless liquid with an intense, warm, sweet, coumarin-like odor.
A cis–trans mixture can be prepared by radical addition reaction of pentanal with crotonic acid followed by reductive cyclization of the resulting ??-oxo acid with sodium boron hydride/sulfuric acid . It is used in aroma compositions, for example, for beverages.

Reported present in cognac, rum, Irish malt, bourbon whiskey, scotch, sherry, port and wine.

80% of a taste panel found whiskey lactone intolerable at 160 ppm

Taste characteristics at 0.5 ppm: woody, coumarinic, coconut, lactonic, creamy and nutty with a toasted nuance.

Tetrahedron Letters, 26, p. 6225, 1985 DOI: 10.1016/S0040-4039(00)95058-5

Methyl octalactoneTM (PFW)