Syntheses of 3,4-Benzotropolones by Ring-Closing Metatheses

Arican, Deniz; Brückner, Reinhard

doi:10.1021/ol400510j

Cited by 31 publications

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“…[14] Likewise,d iene 8,R x = 2 OMe, with am ethallylr ather than allyl groupf urnished the 8methylated benzotropolone 14. This led to the 9-vinylated benzotropolone 12 [14] (yet not to the O-unprotected parent compound 13)a sw ell as to the 8-vinylatedketal 15 [16] (but no closert oa n8 -vinylated benzotropolone). This led to the 9-vinylated benzotropolone 12 [14] (yet not to the O-unprotected parent compound 13)a sw ell as to the 8-vinylatedketal 15 [16] (but no closert oa n8 -vinylated benzotropolone).…”

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“…[11] It appearsa si fn ot each benzotropolone of the substitution pattern 2 is accessible by co-oxidizingcatechol/pyrogallolm ixtures or oxidizing pyrogallols alone. [14] It is outlined in Scheme1.I tp erceives 10 as the enol of an a-diketone and reaches thel atter by hydrolyzing the respective monoketal 9. [7c] Aurantricholone (7) [12] might be another one.…”

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“…However,s ubjecting the a-methylstyrene analogue of diene 8,R x = H, to the same transformations gave the 9methylated benzotropolone 11. [14] Replacing,a lternatively, one vinyl group of type-8 dienes by an ethynyl group allowed ringclosures by enyne metatheses. [14] Replacing,a lternatively, one vinyl group of type-8 dienes by an ethynyl group allowed ringclosures by enyne metatheses.…”

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“…[14] Replacing,a lternatively, one vinyl group of type-8 dienes by an ethynyl group allowed ringclosures by enyne metatheses. Here we disclose-exemplarily-how manipulating the unsubstituted C 8 =C 9 bond of the previously described [14] ring-closure products 18 (Scheme 2) and 23 (Scheme 3) leads to am anifold of 9-(Scheme 5) and 8-functionalized 3,4-benzotropolones (Scheme 6). Here we disclose-exemplarily-how manipulating the unsubstituted C 8 =C 9 bond of the previously described [14] ring-closure products 18 (Scheme 2) and 23 (Scheme 3) leads to am anifold of 9-(Scheme 5) and 8-functionalized 3,4-benzotropolones (Scheme 6).…”

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“…[14] C-Functionalizationsr ealized by this strategy( 11, [14] 14 [14] )o rb ya nalogous enyne metatheses (13, [14] 15 [16] ). Treatment of aT HF solution of cis-24 with DBU at ambient temperature for 2h furnished as ingle bromoolefin 28 in 72 %y ield.…”

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Regioselective Bromination of Benzocycloheptadienones for the Synthesis of Substituted 3,4‐Benzotropolones Including Goupiolone A

Arican

Braukmüller

Brückner

2017

Chemistry A European J

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Type-18 or -23 benzocycloheptadienones are readily prepared by ring-closing olefin metatheses. Adding Br to 23 and eliminating HBr gave the bromoolefin 28 using DBU or its isomer iso-28 using DABCO, both with near-perfect regiocontrol. Both 28 and iso-28 underwent Sonogashira, Suzuki, Negishi, and Heck couplings as well as Pd-catalyzed alkoxycarbonylations. Hydrolysis of the resulting α-ketoketals and enolization of the liberated α-diketones delivered a portfolio of hitherto unknown 3,4-benzotropolones. The 8-ethoxycarbonylated dimethyl-3,4-benzotropolone 50 obtained by this route was dimethylated to give goupiolone A (52). This synthesis encompasses 9 steps from 22, that is, half as many as the only previous synthesis (19 steps). A variant of our route afforded the 1,8-dibromide 54. Coupling with excess phenylboronic acid and ketal hydrolysis provided the diphenylated benzotropolone 56 and suggests a strategy, by which the natural bispulvinone aurantricholone (7) might be reached.

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Regioselective Bromination of Benzocycloheptadienones for the Synthesis of Substituted 3,4‐Benzotropolones Including Goupiolone A

Arican

Braukmüller

Brückner

2017

Chemistry A European J

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ChemInform Abstract: Syntheses of 3,4‐Benzotropolones by Ring‐Closing Metatheses.

Arican

Brueckner

2013

ChemInform

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Syntheses of 3,4-Benzotropolones by Ring-Closing Metatheses. -For the first time, a nonbenzenoid aromatic such as tropolone is obtained via ring-closing metathesis. Using three different approaches, a series of mostly unknown 3,4-benzotropolones is synthesized. -(ARICAN, D.; BRUECKNER*, R.; Org. Lett. 15 (2013) 11, 2582-2585, http://dx.doi.org/10.1021/ol400510j ; Inst. Org. Chem., Albert-Ludwigs-Univ., D-79104 Freiburg/Br., Germany; Eng.) -H. Haber 39-054

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6,7‐Benzotropolone Syntheses Based on Ring‐Closing Metatheses and Four‐Electron Oxidations

et al. 2020

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Four homoallyl ortho-vinylaryl ketones (10a-d) -1,8dienes of sorts -were prepared by several approaches. In the presence of 1-2 mol-% Grubbs-II catalyst, they ring-closed to give 6,7-dihydrobenzocyclohepten-5-ones (11a-d) in 90-96 % yield. With SeO 2 the parent compound (11a) delivered benzocyclohepten-5-one (13a) and/or selenium-containing compounds (18)(19)(20)(21)(22) but no more than traces of 6,7-benzotropolone (5a). However, 5a was accessible from compound 11a via the sodium enolate and allowing it to react with a stream of oxygen [a] Scheme 1. Top: our previously established ring-closing olefin metathesis ("RCM")/ketal hydrolysis route to type-5 6,7-benzotropolones. [9] Underneath: regiocomplementary processings of a type-4 RCM product via the dibromide 7 and the bromoolefins 7 or iso-7 by cross-couplings and hydrolyses giving type-8 or type-iso-8 6,7-benzotropolones, respectively. [10] The Arican routes of Scheme 1 have a major drawback, though, namely the harsh conditions required for hydrolyzing a type-4 ketal in the last step: Liberating the enol required refluxing with 10 equiv. of tosic acid and 100 equiv. of water in acetonitrile for 1 h -2 d. [9,10] These conditions were applicable to certain type-9 or type-iso-9-ketals, as well ( Figure 2). When their substituent R was Et, Ph, CO 2 Me or CO 2 Et, such hydrolyses also proceeded well. [9] However, when their substituent R was CH=CH-CO 2 iPr (in 9a or iso-9a), HC=CH 2 (in 9c or iso-9c) or C≡C-SiMe 3 (in iso-9c) the substrate vanished under hydrolysis conditions without delivering any benzotropolone. [9,10] The C≡C-SiMe 3 -containing ketal 9b was an in-between-case: Its hydrolysis released a benzotropolone as expected but the sidechain R had been converted into C(=O)-CH 3 . [10] Eur.2930 Scheme 2. Can 6,7-benzotropolones 5 be reached via an RCM/oxidation route rather than via the RCM/hydrolysis route of Scheme 1? A 4-e 2 oxidation 11 → 5 would be required overall, but two 2-e 2 oxidations 11 → 12 and 12 → 5 might be used as an alternative. 5.We wondered whether step 2 might be disadvantaged vs. a dehydration delivering the benzotropone 13. While 13 looks like a dead-end at first, it might be re-routable towards 5. This is because unsubstituted benzotropone (13, all R = H) gave unsubstituted benzotropolone (5, all R = H) by endoperoxide formation and an ensuing reduction with thiourea. [11] Consequently, benzotropones 13 appeared as conceivable intermediates of our Scheme-2 strategy towards benzotropolones. A Modified Synthesis of 6,7-BenzotropoloneOur proof-of-principle benzotropolone synthesis by the approach of Scheme 1 delivered the parent compound 5a and is shown in Scheme 3 and Scheme 5. Scheme 3 advances to the RCM product and Scheme 5 supplements its oxidation. Scheme 3. Reaching the RCM product 11a, our synthetic precursor of unsubstituted benzotropolone (5a).Our synthesis began by a salt-free Wittig methylidenation of ortho-bromobenzaldehyde (14, Scheme 3). [12] The resulting ortho-bromostyrene (15) was treated sucessively with nBuLi and the...

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Syntheses of 3,4-Benzotropolones by Ring-Closing Metatheses

Cited by 31 publications

References 42 publications

Regioselective Bromination of Benzocycloheptadienones for the Synthesis of Substituted 3,4‐Benzotropolones Including Goupiolone A

Regioselective Bromination of Benzocycloheptadienones for the Synthesis of Substituted 3,4‐Benzotropolones Including Goupiolone A

ChemInform Abstract: Syntheses of 3,4‐Benzotropolones by Ring‐Closing Metatheses.

6,7‐Benzotropolone Syntheses Based on Ring‐Closing Metatheses and Four‐Electron Oxidations

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