Syntheses of 6,7‐Benzotropolone by Using Ring‐Closing Metathesis Variants Obviating a Strongly Acidic Hydrolysis Thereafter
Abstract A Wittig reaction of 3‐hydroxyphtalide (11) gave ortho‐styrene‐2‐carboxylic acid (12). Its Weinreb amide13 acylated heterosubstituted methyllithiums. This led to aryl “methyl” ketones whose sp3‐carbon was substituted by Cl+OMe (in14 a), 2×Cl (in14 b), OtBu (in17 a), SPh (in17 b) or SO2 Ph (in17 c). The enolates of these ketones were C‐allylated. This furnished the benzene‐fused nona‐1,8‐dienones7 a– b and9 a– c, respectively. Ring‐closing metatheses provided the corresponding benzocycloheptadienones8 a‐ b and10 a– c. Their ketone moieties were α,α‐disubstituted (in8 a– b) or α‐monosubstituted (in10 a– c). Each substitution pattern allowed to generate the hydroxyenone motif of the corresponding benzocycloheptatrienone—or 6,7‐benzotropolone—6 a: The MeO‐ and PhS‐containing benzocycloheptadienone8 a gave 6,7‐benzotropolone methyl ether (15) by sulfoxide formation and pyrolysis;15 was demethylated with BCl3. The same intermediate resulted from the dichlorobenzocycloheptadienone8 b and NaOMe. The benzocycloheptadienone10 a was de( tert‐butylated) with formic acid; a subsequent Pfitzner‐Moffatt oxidation completed 6,7‐benzotropolone (6 a) once more. The PhS‐containing benzocycloheptadienone10 b was α‐acetoxylated with Pb(OAc)4; the resulting O,S‐acetal gave 6,7‐benzotropolone (6 a) by hydrolysis. The PhSO2‐containing substrate10 c was deprotonated whereupon an oxidation with Me3 Si−O−O−SiMe3 gave 6,7‐benzotropolone (6 a)..
| Medienart: |
E-Artikel |
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| Erscheinungsjahr: |
2022 |
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| Erschienen: |
2022 |
| Enthalten in: |
Zur Gesamtaufnahme - volume:2022 |
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| Enthalten in: |
European Journal of Organic Chemistry - 2022(2022), 17 |
| Beteiligte Personen: |
Koblischek, Philip [VerfasserIn] |
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| BKL: |
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| Anmerkungen: |
© 2022 Wiley‐VCH GmbH |
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| Umfang: |
16 |
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| doi: |
10.1002/ejoc.202101070 |
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| funding: |
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| Förderinstitution / Projekttitel: |
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WLY005074908 |
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| 520 | |a Abstract A Wittig reaction of 3‐hydroxyphtalide (11) gave ortho‐styrene‐2‐carboxylic acid (12). Its Weinreb amide13 acylated heterosubstituted methyllithiums. This led to aryl “methyl” ketones whose sp3‐carbon was substituted by Cl+OMe (in14 a), 2×Cl (in14 b), OtBu (in17 a), SPh (in17 b) or SO2 Ph (in17 c). The enolates of these ketones were C‐allylated. This furnished the benzene‐fused nona‐1,8‐dienones7 a– b and9 a– c, respectively. Ring‐closing metatheses provided the corresponding benzocycloheptadienones8 a‐ b and10 a– c. Their ketone moieties were α,α‐disubstituted (in8 a– b) or α‐monosubstituted (in10 a– c). Each substitution pattern allowed to generate the hydroxyenone motif of the corresponding benzocycloheptatrienone—or 6,7‐benzotropolone—6 a: The MeO‐ and PhS‐containing benzocycloheptadienone8 a gave 6,7‐benzotropolone methyl ether (15) by sulfoxide formation and pyrolysis;15 was demethylated with BCl3. The same intermediate resulted from the dichlorobenzocycloheptadienone8 b and NaOMe. The benzocycloheptadienone10 a was de( tert‐butylated) with formic acid; a subsequent Pfitzner‐Moffatt oxidation completed 6,7‐benzotropolone (6 a) once more. The PhS‐containing benzocycloheptadienone10 b was α‐acetoxylated with Pb(OAc)4; the resulting O,S‐acetal gave 6,7‐benzotropolone (6 a) by hydrolysis. The PhSO2‐containing substrate10 c was deprotonated whereupon an oxidation with Me3 Si−O−O−SiMe3 gave 6,7‐benzotropolone (6 a). | ||
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