As an alternative to the catalytic procedure,"' directed multistep pagodane-dodecahedrane transformations (routes A and/or B/C in Ref. [2]) are a current goal: for example, via the intermediates 2-5 (Fig. 1 ) in the case of the basic skeletons 116. At intermediate 5 , this route converges with Puquette's dodecahedrane synthesis, which was recently considerably improved for step 5-6, which involves dehydrogenation and simultaneous C-C bond formation.[31 The calculated (MM2)I4] molecular structures (Fig. I ) clearly reveal how, with iTcreasing expansion of the "waist" of 1 (1.55 A) to 3.49 A in 4, the distance between the opposing methylene C atoms (which are eventually to undergo direct C-C bond formation) and their syn hydrogen atoms becomes increasingly small. The enthalpies of formation, AH?, decrease continuously on going from 1 to the "stabilomer"[sl 6 , while the strain energies, E, , , , decrease discontinuously (Fig. 1). The increase of E,,, in going from 2 via 3 to 4, which is primarily a consequence of the increasing transannular and vicinal H / H interactions, necessarily implies considerably reduced "olefinic strain (OS)"'4.51 for 2/3 (OS= I1.4/-.13.9 kcal/ mol). The diene 2 is of further structural interest because the C = C bonds, held in an overall very rigid molecular skeleton, have an unusually small transannular distance, with ideal colinear orientation of the n orbita1s;'"l the calculated value of 2.62 A, however, is probably at least 0. l A too The (transannular) strain inherent in 2 and 3 is manifested in a pyramidalization of the olefinic centers by about 10" and So, respectively. Comparable energetic and structural relationships were calculated for the reaction sequence starting from the diketone 7 and proceeding via the intermediates 10-12. After initial model studies,"] a preparatively efficient entry into the reaction sequence 1 + 6 was made possible by the finding that [l.l.l.l]pagodane 1 reacts with bromine (in very large excess) regiospecifically and quantitatively to give the crystalline, moisture-sensitive dibromide 8 (m.p. = 240-241 "C (dec.)); the reaction occurs thermally within days and upon irradiation (300-W Osram Vitalux lamp, pyrex filter) within minutes. Under standard conditions (Zn, dimethylformamide, 160°C, 3 h), 8 is converted in high yield (89%) into the crystalline bissecododecahedradiene 2 (m.p. =260°C (dec.)), which, especially in solution, is sensitive toward oxidation. Analogously, the pagodanedione 7 is transformed, via the dibromide 9 (m.p. =294-29S°C (dec.), loo%), into the dienedione 10 (m.p. = 322-323 "C, 85%)."I Heating or irradiation of the dibromides 8/9 results in loss of bromine with re-formation of 117 ; this finding explains why a large excess of reagent is necessary in their preparation.