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In memory of Professor Franz Sondheimer (6.V. 83) SummaryThe radical anions of 5,6-didehydrobenzocyclooctene (3), 5,6,9,10-tetradehydrobenzocyclooctene (4) and 1,4,7,10-tetramethy1-5,6-didehydrodibenzo [u, el-cyclooctene (6) were prepared in situ from dibromo-precursors and have been characterized by ESR and ENDOR spectroscopy.Introduction. -Dehydrocyclooctatetraenes and their benzo-derivatives have received much attention in the last few years [I]. Insertion of a triple bond into the unsaturated eight-membered ring increases its tendency to flatten; concurrently, the propensity of the hydrocarbon to undergo addition, dimerization and rearrangement reactions is enhanced. The reactivity is, in general, lowered by introducing a second triple bond and by fusing benzene rings to the dehydrocyclooctatetraene 71-system 111.The transient existence of cyclooctatrienyne (l), the simplest member of the series, has been proved by trapping 1 with various reagents [2]. Attempts to synthesize cycloocta-1 ,5-diene-3,7-diyne (2) [3] and 5,6-didehydrobenzocyclooctene (3) [4] have failed so far, while 5,6,9,10-tetradehydrobenzocyclooctene (4) was obtained as a rapidly decomposing oil [ 5 ] . 5,6-Didehydrodibenzo [a, e]cyclooctene (5) and 5,6,11,12-tetradehydrodibenzo[a, e]cyclooctene (7) were both isolated in crystalline form 161, but only the diyne 7 is relatively stable at room temperature. In addition to 5, its 1,4,7,lO-tetramethyl derivative (6) has quite recently been prepared [7]. It is noteworthy that the first synthesis claimed for 6 [8] yielded, in fact, the isomeric 1,4,6,9-tetramethylbenzo [blbiphenylene 191.The radical anions 1 8 [lo], 5 9 [ l l ] and 7 9 [ l l ] have been characterized by ESR spectroscopy; the hyperfine data are consistent with a planar eight-membered

Table 1. Intercalation compounds of a-RuCI,: Dependence of interlayer spacing d upon guest species [atomic ions hydrated, or solvated with dimethy1 sulfoxide (DMSO) or formamide (FA); molecular guest ions unsolvated; Cp = cyclopentadienyl ligand]; interlayer spacing in empty host lattice d = 573 pm. Guest Na+

Dedicated to Prof. Edgar Heilhronner on the occasion of his 70th birthday (4.11.91) Reduction of tribenzo[a,c,e]cyclooctene (2) and its 2,3-and 1,4-dimethyl derivatives (4 and 5 ) , as well as of l,l-dimethyl-l0,11-propane-2,2-diylidene-lH-benzo[5,6]cycloocta[ 1,2,3,4-deflfluorene (6) and its 5,6-didehydro derivative (7) was followed by cyclic voltammetry. The radical anions of these compounds and those of their derivatives (D)2, (D)5, and (D)6, deuterated at C(9) in 2 and 5 or in the corresponding position of 6, have been characterized with the use of ESR, ENDOR, and TRIPLE-resonance spectroscopy. The cyclic-voltammetic and proton-hyperfine data are consistent with the increasing deviations of the radical anions from planarity in the order 6:,

Treatment of A‐nor‐Δ3(5)‐cholestene‐2‐one (1) with alkaline hydrogen peroxide gave 3β,5‐epoxy‐A‐nor‐cholestane‐2‐one (2) and the epoxylactone 3 (BAEYER‐VILLIGER reaction). LiAlH4‐reduction of 2 yielded A‐nor‐5β‐cholestane‐2β,5‐diol(4) (main product) and A‐nor‐5β‐cholestane‐2α,5‐diol (5). LiAlH4‐reduction of 1 led mainly to A‐nor‐Δ3(5)‐cholestene‐2α‐ol (8). Catalytic hydrogenation of 8 gave the known A‐nor‐5α‐cholestane‐2α‐01 (10), A‐nor‐5β‐cholestane‐2α‐01 (11) (main product), A‐nor‐5β‐cholestane (9) and A‐nor‐5β‐cholestane‐2‐one (12). By LiAlH4‐reduction of the ketones 12 and 13 the two additional alcohols 14 and 15 were obtained.