Synthesis and Chiroptical Properties of Dimethyl 8,12‐Diphenylbenzo[ d ]heptalene‐6,7‐dicarboxylate

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Dedicated to Richard Neidlein on the occasion of his 65th birthday (21.VII.95) It is shown that the 2-(hydroxymethyl)-l-methylazulenes 6 are being oxidized by activated MnO, in CH,Cl, at room temperature to the corresponding azulene-l,2-dicarbaldehydes 7 (Scheme 2 ) . Extension of the MnO, oxidation reaction to I-methyl-and/or 3-methyl-substituted azulenes led to the formation of the corresponding azulene-1-carbaldehydes in excellent yields (Scheme 3 ) . The reaction of unsymmetrically substituted 1,3-dimethylazulenes (cf. 15 in Scheme 4 ) with MnO, shows only little chemoselectivity. However, the observed ratio of the formed constitutionally isometric azulene-I-carbaldehydes is in agreement with the size of the orbital coefficients in the HOMO of the azulenes. The reaction of guaiazulene (18) with MnO, in dioxane/H,O at room temperature gave mainly the expected carbaldehyde 19. However, it was accompanied by the azulene-diones 20 and 21 (Scheme 5). The precursor of the demethylated compound 20 is the carbaldehyde 19. Similarly, the MnO, reaction of 7-isopropyl-4-methylazulene (22) as well as of 4,6,8-trimethylazulene (24) led to the formation of a mixture of the corresponding azulene-l,5-diones and azulene-1,7-diones 20j23 and 25/26, respectively, in decent yields (Schemes 6 and 7 ) . No MnO, reaction was observed with 5,7-dimethylazulene.

Section: Experimental Partmentioning

confidence: 99%

Section: Experimental Partmentioning

confidence: 99%

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Reaction of Hydroxymethyl‐ and Alkyl‐Substituted Azulenes with Manganese Dioxide

Fallahpour

Sigrist

Hansen

1995

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“…of Ph,C+BF, with respect to the mixture of 23a-d was applied, 28a/28b (70%) were, beside Ph,CH, again the main components in the reaction mixture after treatment with Me,N. [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.…”

Section: D23bmentioning

confidence: 99%

Synthesis of Benzo[a]heptalene

Guspanová

Knecht

Lagana

et al. 1997

Dedicated to Oscar Jeger on the occasion of his 80th birthday (7. v. 97) Benzo [a]heptalene has been synthesized by two different approaches. The first one follows a pathway to hexahydrobenzo [a]heptalenone 19a that has been already described by Wenkert and Kim (Scheme f). Indeed, 19a was obtained in a mixture with its double-bond-shifted isomer 19b. Reduction of this mixture to the corresponding secondary alcohols 26a/26b and elimination of H,O lead to a mixture of the tetrahydrobenzo[a]heptalenes 23a-d (Scheme 7 and 8). Reaction of 23a-d with 2 equiv. of triphenylmethylium tetrafluoroborate in boiling CHCl,, followed by treatment with Me,N in CH,CI,, generated directly 2, unfortunately in a mixture with Ph,CH that could not be separated from 2 (Scheme 10 and ff). The second approach via dimethyl benzo[u]heptalene-6,7-dicarboxylate (30) (Scheme fZ) that was gradually transformed into the corresponding carbaldehydes 37 and 43 (Scheme 14) both of which, on treatment with the Wilkinson catalyst [RhCl(PPh,),] at 130" in toluene, smoothly decarbonylated, finally gave pure 2 as an unstable orange, viscous oil. UV/VIS, NMR, and mass spectra of 2 are discussed in detail (cf. Chapt. 3).

“…a) 180-208" in tetralin or decalin or looo in MeCN in the presence of2 mol-% of [RuH2(Ph3P),] (6). b) 180-208" in tetralin or decalin.…”

Section: H (E)/(z)-5 (6%)mentioning

confidence: 99%

Thermal and Ru‐catalyzed Reactions of Styryl‐Substituted Azulenes with Dimethyl Acetylenedicarboxylate

Briquet

Hansen

1994

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The thermal reaction of I-[(E)-styryl]azulenes with dimethyl acetylenedicarboxylate (ADM) in decalin at 190-200" does not lead to the formation of the corresponding heptalene-1,2-dicarboxylates (Scheme 2). Main products are the corresponding azulene-l,2-dicarboxylates (see 4 and 9), accompanied by the benzanellated azulenes rrans-lOa and trans-1 1, respectively. The latter compounds are formed by a Diels-Alder reaction of the starting azulenes and ADM, followed by an ene reaction with ADM (cf Scheme 3 ) . The [RuH2(PPh3),]-catalyzed reaction of 4,6,8-trimethyl-l-[(E)-4-R-styryl]azulenes (R=H, MeO, CI; Scheme 4 ) with ADM in MeCN at 110' yields again the azulene-1,2-dicarboxylates as main products. However, in this case, the corresponding heptalene-1,2-dicarboxylates are also formed in small amounts (3-5 YO; Scheme 4 ) . The benzanellated azulenes rmns-l0a and rrrms-lOb are also found in small amounts (2-3 %) in the reaction mixture. ADM Addition products at C(3) of the azulene ring as well as at C (2) of the styryl moiety are also observed in minor amounts (1-3%). Similar results are obtained in the [R~H~(PPh~)~]-catalyzed reaction of 3-[(E)-styryl]guaiazulene ((E)-8; Scheme 5 ) with ADM in MeCN. However, in this case, no heptalene formation is observed, and the amount of the ADM-addition products at C(2) of the styryl group is remarkably increased (29%). That the substituent pattern at the seven-membered ring of ( E ) -8 is not rcsponsible for the failure of heptalenc formation is demonstrated by the Ru-catalyzed reaction of 7-isopropyl-4-methyl-I-[(E)-styryl]a~ulene ((E)-23; Scheme 11) with ADM in MeCN, yielding the corresponding heptalene-1,2-dicarboxylate (E)-26 (10%). Again, the main product is the corresponding azulene-1,2-dicarboxylate 25 (20%). Reaction of 4,6,8-trimethyl-2-[(E)-styryl]azulene ((E)-27; Scheme 12) and ADM yields the heptdhe-dicarboxylates (E)-JOA/B, purely thermally in decalin (28 %) as well as Ru-catalyzed in MeCN (40%).Whereas only small amounts of the azulene-1,2-dicarboxylate 8 (1 and 5%, respectively) are formed, the corresponding benzanellated azulene trans-29 ist found to be the second main product (21 and lo%, respectively) under both reaction conditions. The thermal reaction yields also the benzanellated azulene 28 which is not found in the catalyzed variant of the reaction. Heptalene-l,2-dicarboxylates arc also formed from 4-[(E)-styryl]azulenes (e.g. (E)-33 and (E)-34; Scheme 14) and ADM at 180-190" in decalin and at I10"in MeCN by [RuH,(PPh3),] catalysis. The yields (30%) are much bctter in the catalyzed reaction. The formation of by-products (e.g. 3941; Scheme 14) in small amounts (0.5-5 %) in the Ru-catalyzed reactions allows to understand better the reactivity of zwitterions (e.g. 42) and their tricyclic follow-up products (e.g. 43) built from azulenes and ADM (qf: Scheme 15). ') Part of the Ph. D. thesis of A.A.S.B., Univcrsity ofZurich. 1993 HBLVETICA CHIMICA ACTA -Vol. 77 (1994) Resultsand Discussion. -2.1. l-Styryl-Substituted Azulenes. -The thermal reaction of 4...