In 2002, pyrrocidine A and B were isolated from the fermentation broth of a fungus, LL-Cyan 426, as antimicrobial agents against Gram-positive bacteria including drug-resistant strains. Structural features of pyrrocidines are tricyclic decahydrofluorene core (ABC-ring) and 13-membered macrocycle containing para-substituted aryl ether moiety. The complex molecular architecture of these compounds makes them very attractive target molecules for total synthesis. We report herein the stereoselective synthesis of decahydrofluorene 21 which provides the first entry to the ABC-ring moiety of pyrrocidines. The synthesis of 21 commenced with the construction of the C-ring moiety. The cyclic carbon skeleton was synthesized via Diels-Alder reaction between dimethyl-substituted Danishefsky-Yan diene 7 and trisubstituted alkene 8 to afford a diastereomeric mixture of cyclohexenone 10a-b. The ketone 11a possessing the desired configuration was mainly obtained by thermal epimerization of the diastereomeric mixture of 11a-c. Ring-closing metathesis reaction of diene 15, followed by Dess-Martin oxidation afforded the cyclic dienophile 16. Diels-Alder reaction between Danishefsky-Kitahara diene 5 and bicycloenone 16, and the sequential acidic treatment gave diketone 4, establishing the tricyclic carbon framework of 21. Owing to the inherent convex-face selectivity of cis-fused bicyclic AB-ring moiety of 4, nitrile 19 was stereoselectively synthesized in several steps. Vinyl group was introduced to 4 from concave face selectively, avoiding the adjacent cyano group, in two steps to afford ketone 20. The reduction of ketone group from convex face of 20, followed by Chugaev elimination furnished decahydrofluorene 21.