Dedicated to Arnold Brossi on the occasion of his 70th birthday (23. IX. 93) 6,lO-Diphenylbenz[u]azulene (3) was reacted with dimethyl acetylenedicarboxylate (ADM) in the presence of 2 mol-% of [RuH2(PPh3),] in MeCN at 100' to yield a 7:1 mixture of dimethyl 2,6-diphenyl-9,10-benzotricyclo-[6.2.2.0',7]dodeca-2,4,6,9,1 I-pentaene-1 1,12-dicarboxylate (4) and dimethyl 8,12-diphenylbenzo[d]heptalene-6,7dicarboxylate (5; Scheme 2). The tricycle 4, when heated in DMF at 150" for 1 h led to the formation of 81.5% of the heptalene-6,7-dicarboxylate 5 and 15 YO of the starting azulene 3. No rearrangement of tricycle 4 was observed.when it was heated at temperatures up to 180" in pseudocumene. The heptalene-6,7-dicarboxylate 5 was easily separated into its antipodes (I'M)-and (MP)-5 on a Chirucef column (cf. Fig. 2). On heating at 150" for 1 h, (MP)-5 showed no racemization at all. The Ru-catalyzed reaction of benz[a]azulene (6) with ADM led to the formation of dimethyl 9,10-benzotricyclo[6.2.2.0'~7~dodeca-2,4,6,9,1 l-pentaene-l1,12-dicarboxyIate (7; Scheme 3 ) . However, the formation of the corresponding heptalene-6,7-dicarboxylate could not be observed.Introduction. -Recently, we described the chemical transformation of colchicine (1 ; R=H) and some of its 4-alkyl derivatives into their underlying parent structures 2, i.e. the corresponding 1,2,3,9,1O-pentamethoxybenzo[d]heptalenes (Scheme I ) [I] [2]. Since compounds 2 represent, to the best of our knowledge, the first members of the class of benzo[d]heptalenes2), we were interested in another synthetic access to this class of compounds, which would also represent the basis of a new and variable approach to colchicinoid-type compounds3). Our recent success in the improvement of the synthesis
It is shown that sodium (methoxycarbony1)cyclopentadienide (l), which is easily accessible from sodium cyclopentadienide and dimethyl carbonate in THF, reacts with 2,4,6-trisubstituted pyrylium tetrafluoroborates Z a 4 in boiiing MeOH to afford the corresponding methyl ~izulene-2-carboxylates 4 a 4 in good yields. The corresponding 1-carboxylates 3 were not found (cf. Schemes I and 2)Whereas the synthesis of azulenes, substituted at the seven-membered ring, can easily be accomplished by the reaction of 2,4,6-trisubstituted pyrylium salts with sodium cyclopentadienide in THF (cf. [l] [2]) or of N-alkylpyridinium salts with sodium cyclopentadienide in DMF (cf. [l] [3]), it is much more problematic to react substituted cyclopentadienides under the above mentioned conditions, since, in general, mixtures of the 1-and 2-substituted azulenes are obtained which are difficult to separate (cf. [l] [4]). The reaction of 2,4,6-trimethylpyrylium perchlorate with sodium methylcyclopentadienide under carefully controlled conditions in THF leads to the formation of 2,4,6,8-tetramethylazulene in moderate yields [2a]*).We were interested in a plain synthesis of 4,6,8-trisubstituted methyl azulene-2-carboxylates and checked the reaction of sodium (methoxycarbony1)cyclopentadienide (l), which is easily accessible by the reaction of dimethyl carbonate and sodium cyclopentadienide in THF at 70" [5], with 2,4,6-trimethylpyrylium tetrafluoroborate (2a). In THF, we obtained only mixtures of the corresponding 1-and 2-carboxylates 3a and 4a (Scheme 1 ; c j also [6]).However, when the reaction was run in boiling MeOH, only the 2-carboxylate 4a was formed in 47% yield. It was deposited as a microcrystalline powder directly from the boiling solution. It was pure and showed no traces of the 1-carboxylate 3a. The examples in Scheme 2 show that the described procedure can generally be applied to the synthesis of 4,6,8-trisubstituted azulene-2-carboxylates.We assume that, in the protic solvent MeOH, 1 reacts in its 6-methoxyfulvene 6-oxide form, i.e., it should attack the corresponding pyrylium salts with its C(3,4)-atoms, favoring the formation of the 2-carboxylates.The azulene-2-carboxylates can be reduced in one step to the corresponding 2-methylazulenes with sodium dihydridobis(2-methoxyethoxy)aluminate in the presence of AICI, in toluene (cf. Exper. Part). ') 2,New address: Harvard University, Department of Chemistry, 12 Oxford Street, Cambridge, MA 02138, USA. Our own experience showed us that the corresponding pyrylium tetrafluorohorate always yields mixtures of 1,4,h,X-and 2,4,6,8-tetra1nethylazulene.
Dcdicated tu Duilio Arigoni on the occasion of his 65th birthday (2. VIII.93) [Rh'(q 5-azulene)(cod)]+BF; complexes 3 a s (cod = (Z,Z)-cycloocta-1 ,S-diene) have been synthesized by reaction of [Rh'(cod)]+BF; in THF with the corresponding azulenes la-g ( Table I ) . The structure of [Rh'(cod)(q5-guaiarulene)]+BF~ (3a) has been determined by X-ray diffraction analysis ( Fig. I and 2). The Rh-atom is oriented above the five-membered ring of the azulene with almost equal Rh-C distances to all five C-atoms of the ring. The (Z,Z)-cycloocta-1,s-diene ring occurs in two enantiomorphic distorted (C2u+C2) tub conformations in the crystals (Fig. 3 ) . In CDCI, solution, the cod ligand in the complexes 3 shows a dynamic behavior on the 'H-NMR time scale which is best explained by rotation of the cod ligand relative to the azulene ligands around an imaginary cod-Rh-azulene axis. The new complexes 3 catalyze the formation of heptalene-1,2-dicarboxyIates 2 from dimethyl acetylenedicarboxylate (ADM) and the corresponding azulenes 1 just as effectively as [RuH,(PPh,),] and the analogous [RhH(PPh,),] complex in MeCN solution (Tahle 3 ) . On grounds of simplicity, 3 can be generated in sifu, when [RhCl(cod)I2 is applied as catalyst (Table 3 ) .Introduction. -Recently, we have shown that the yield of heptalene-l,2-dicarboxylates 2 formed from azulenes 1 and dimethyl acetylenedicarboxylate (ADM) in apolar solvents at temperatures > 180" can be improved substantially, when the reaction is carried out in the presence of a catalytic amount of [RuH,(PPh,),] in a polar aprotic solvent such as MeCN (Scheme 1 ) [l]. The reaction of l-(tert-butyl)-4,6,8-trimethylazulene with ADM in the presence of the catalyst yielded, even at 25", dimethyl 11-(tertbutyl)-2,4, 6-trimethyltricyclo[6.2.2.01 ']dodeca-2,4,6,9,11 -pentaene-9,1O-dicarboxylate, which represents the Diels-Alder-type adduct of ADM and the five-membered ring of the azulene. Since this type of adduct is also the established primary intermediate in the
Biphenyls with only two substituents at the −peri×-position normally show rotation about their chiral axis at room temperature. Using vibrational circular dichroism (VCD), we found no evidence for rotation of (P)-2'-in CDCl 3 about its chiral axis due to stabilization by intramolecular H-bonding. All rotamers of 1 were calculated at the DFT level, and, from these optimized structures, the VCD spectra were calculated and compared to the measured VCD spectra. The best agreement between calculated and measured spectra is obtained when two rotamers are present in solution. These rotamers differ primarily in their intramolecular H-bonding interactions, having either OH ¥¥¥ N (the form present in the solid state) or OH ¥¥¥ O H-bonds, i.e., a rotation of the heterocycle in 1 takes place in solution.
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