Synthesis of 4,6,8‐Trisubstituted Methyl Azulene‐2‐carboxylates

Abstract

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.

A Detailed Investigation of the Reaction of 5,9-Diphenylbenz[a]azulene with Dialkyl Acetylenedicarboxylates Leading to Dialkyl 8,12-Diphenylbenzo[a]heptalene-6,7-dicarboxylates

“…82 (1999) 2280 6 ) We found this effect also with other azulenes and ADM (cf. [14] , respectively. The thermal rearrangement of 2a to 9a at 1008 is twice as fast as that of 2c to 9c (vide supra).…”

“…The main reaction path is determined with high periselectivity by the HOMO(azulene) and LUMO(acetylenedicarboxylate) interaction that leads to the reversible formation of the primary intermediates of type 2a (27a) in a [4 2] manner. Other pericyclic processes do not play a significant role despite the fact that they result in the formation of products of type 12a (29a) or intermediates such as 13a (25a) which display much larger DH 0 f differences with respect to the reactants (1(24) ADM ) 14 E Me groups of the acetylene unit cause significant differences in the DDH 0 f values 14 ). Fig.…”

Synthesis of Benzo[a]heptalene

“…IR (film): 3068w, 3000m, 2951s, 2844w, 1738vs, 1725vs, 1635s, 1484m, 1 4 3 6~ 1365~1, 1250vs, 1197vs, 1152vs, 1069w, 987~1, 900m, 836w, 770.7, 659vw, 604vw1, 489vw. 346 (18, [M(ll) + NH,]+), 333 (18), 332 (100, [M(DME) + NH,]+), 329 (7, [M(11) + HI+), 316 (6), 315 (27, [M(DME) + HI'), 300 (16), 283 (24), 282 (7).…”

“…[5]. The reaction is also applicable to benz [a]azulene (31) itself and dimethyl acetylenedicarboxylate (ADM) [7] (see also [6]) and opens an easy access to 30 particularly, in view of a new synthesis of 31 that has been developed by us [22] (see also [23] showed that the thermal reaction in aromatic hydrocarbons such as toluene gave the best yields of the benzo[a]heptalenedicarboxylates with a minimum number of by-products (see also [8] [24] [23]), since heptafulvene shows exactly this type of periselectivity in cycloaddition reactions (cf. [25]).…”

Laser control in open quantum systems: preliminary analysis toward the Cope rearrangement control in methyl-cyclopentadienylcarboxylate dimer

“…We thus have prepared the corresponding anion, lithium carbomethoxycyclopentadienide (4), by treatment of cyclopentadiene with sodium hydride in THF, followed by addition of dimethyl carbonate [35]. We thus have prepared the corresponding anion, lithium carbomethoxycyclopentadienide (4), by treatment of cyclopentadiene with sodium hydride in THF, followed by addition of dimethyl carbonate [35].…”