Dedicated to Professor Gunther Wilke on the occasion of his 60th birthday "Octabisvalene" A (X = H),Ii1 which is still unknown, is the third saturated and highly strained (Est = 130-140 kcal/mol) valence isomer of cyclooctatetraene (the others being cubane and cuneane).l2l Starting from cis-benzenetrioxide 1 , we have now achieved the synthesis of the first octabisvalene derivative 7 (X = SOzC6H5).[31The route shown in Scheme 1 is based on the finding (cf. the preparation of the carbocyclic cis-tris-o-homobenzene skeleton B from 1)[41 that the bicyclic, crystalline trio1 2a can be obtained in nearly quantitative yield by reaction of 1 with five equivalents of phenyl~ulfonylmethyllithium~~~ [tetrahydrofuran (THF), -2O-2O0C, 2 d, m.p. = 232"C, Jz.z = 2.6, J3,4 = 12, J4,5 = 10.5 Hz]. The phenylsulfonyl groups were expected, inter aha, to favor the a-deprotonation in 3b, 4, and 5 (as observed in the formation of 2a) over competing rnetalations. 2a was transformed into the acetal 2b (loo%), which was then esterified to 2c (87%). 2c was cyclized to 3b with two equivalents of lithium diisopropylamide (LDA) (THF, -2O"C, 30 min, 90%, m.p. = 23 1 "C, J4,5 = 0 Hz). The diol 3a (loo%), the bissulfonate 3c (>90%), and (via three steps)@] the epoxide 4 (53%, m.p. = 245 "C, Ji,2 z 0, J,,9 = 4 Hz) can be obtained from 3b by standard procedures.In the endo-6-carbanion of 4, the stereoelectronic situation for cyclization to 5a (substitution at C-4) was considered, a priori, favorable: ['] indeed, this step is highly selective using four equivalents of n-butyllithium (THF, -78"C, 30min, 89%, <5% addition of n-BuLi, m.p.=191"C, 52,4=3.5, J4.5=3.5, J2,,=3.8, J5,6=3.5, iJc.4, = 2 10 Hz). Thus, there is no evidence for four-membered-ring formation (substitution at C-2 of 4), inversion of the anion, or o-TI isomerization (which is plausible in the case of the ex0 anion).'*] Not unexpectedly, the high acidity of 4-Hf9I in 5a, b and of 4-H and 8-H in 7 (and also
10of the 0-phenyl protons) causes complications in the ring closure to 7 . HID-Exchange experiments with 5b show that the deprotonation to 8b is faster than to 9b. The carbanion 8b can be trapped as silyl derivative l l b by metalation in the presence of (CH3),SiCI1"] (2 equivalents of lithium tetramethylpiperidide, THF, -78"C, 2 h); l l b (40% along with 5b) is of interest as a C-4 protected precursor of 7 . 6a (J2,5=4 Hz, endo configuration of the silyl group confirmed by NOE) is formed from 5a and two equivalents of n-BuLi after addition of (CH3)3SiOS02CFi; l l a (& = 3.7 Hz) is formed along with several R(X)-ortho-silylated products from 5a and two equivalents n-BuLi after addition of (CH,),SiCI. 6a and l l a are isolated by chromatography (20% and 42%, respectively). Upon treatment of 5b with sufficiently strong bases (1 -2 equivalents of nBuLi, LDA) under various conditions, decomposition occurs almost instantaneously. Presumably, the dicarbanion 10b is highly labile. The monocarbanion 9b was therefore generated by treatment of 6b with "dry" (ca. 0.2 equivalents of HzO) t...
