Spiroacetal biosynthesis: (+/-)-1,7-dioxaspiro[5.5]undecane in Bactrocera cacuminata and Bactrocera oleae (Olive Fruit Fly).

[reaction: see text] A biosynthetic scheme rationalizing the formation of (+/-)-1,7-dioxaspiro[5.5]undecane (5) in the fruit fly species Bactrocera cacuminata and Bactrocera oleae (olive fruit fly) is presented. Incorporation studies with deuterium-labeled keto aldehyde (10), 1,5-nonanediol (11), and 1,5,9-nonanetriol (12), and our previous finding that both oxygen atoms of 5 originate from dioxygen, are strongly evidentiary. The racemic condition of the natural spiroacetal 5 is accounted for, and inter alia, it is demonstrated that dihydropyran (18) is not an important intermediate en route to 5.