The synthesis of natural acuminolide and 17-O-acetylacuminolide is reported. Commerically available (+)-sclareolide was converted to epoxy alcohol 3, which upon acid-catalyzed cyclization afforded tricycle 14. Reaction of 14 with 1O2 in the presence of a hindered base gave an inseparable mixture of acuminolide 1a and 16-epiacuminolide 1b in a 70:30 ratio. Chromatographic separation of the diacetates of 1a and 1b afforded pure 18a and 18b. An analogous reaction sequence was used in the synthesis of 17-O-acetylacuminolide (2a) and 16-epi-17-O-acetylacuminolide (2b).

A stereoselective radical cascade cyclization to 5alpha-pregnanes is presented. Oxidative free radical cyclization of an appropriately substituted chloro cyano ester polyene was used to introduce the all trans stereochemistry in the steroid nucleus. The cyano group was utilized to introduce a C-8beta angular hydrogen, while the chloro ester moiety served as an entry to the geminal hydrogens at C-4.

A cascade radical approach to d,l-norlabdane oxide and related odorants is reported. Oxidative radical cyclization of polyene 4 with Mn(III) and Cu(II) afforded exclusively bicycle 3, which upon acid treatment gave tricycle 2 possessing the norlabdane oxide skeleton with a modified A-ring system. Tricycle 2 was ultimately converted to d,l-norlabdane oxide 1 and to several new A-ring labdane oxides as potential odorants.

A stereoselective radical cascade cyclization of polyene 6, containing an α,β-unsaturated cyano group, was employed to control six contiguous chiral centers and to introduce a C-8 angular CN group in tricycle 7. The cyano group was ultimately utilized as an entry to a C-8 angular hydroxymethyl group. Compound 7 was converted into two key tetracycles 22 and 25, respectively, each possessing an intact D-furan ring system and containing the necessary functionality for further chemical elaboration to the highly oxygenated spongians 1-5.

Advanced Tetracycles in a Stereoselective Approach to d,l-Spongiatriol and Related Metabolites: The Use of Radicals in the Synthesis of Angular Electrophores.-The readily prepared triene (II) is subjected to radical cyclization providing the products (III) and (IV) with total control of six contiguous chiral centers. After deprotection and chromatographic separation, product (V) is converted to the key intermediate furan (IX). The latter can be transformed to the tetracycles (X) and (XI) possessing the necessary functionality for further elaboration to highly oxygenated spongians. Thus, the C-8 angular CN group is utilized to introduce a C-8 hydroxymethyl or C-8 aldehyde function. -(ZORETIC, P. A.; ZHANG, Y.; FANG, H.; RIBEIRO, A. A.; DUBAY, G.; J.