Abstract:
The synthesis of spiroacetals has attracted considerable synthetic interest due to their presence in a wide range of biologically active natural products such as polyether antibiotics, marine and plant toxins, and the antiparasitic agents the avermectins and milbemycins.1 Many of these spiroacetals, notably the fruit fly pheromones2 and the avian toxins, the talaromycins,3 contain hydroxylated 1,7-dioxaspiro[5.5]undecane ring systems. Griseusins A (1) and B (2), produced by a strain of Streptomyces griseus, are members of the pyranonaphthoquinone family of antibiotics and are active against Gram-positive bacteria, pathogenic fungi, and yeasts.4 Another distinguishing feature of these antibiotics is the presence of an oxygenated 1,7-dioxaspiro[5.5]undecane ring system. Our synthetic approach to the griseusins hinged on a stereoselective hydroxylation of unsaturated spiroacetal 3; thus, an examination of the hydroxylation of simpler 1,7-dioxaspiro[5.5]undec-4-enes using Woodward−Prevost5 methodology (Scheme 1) is reported herein. To date there has been no study of this reaction on a spiroacetal ring system.
