Syntheses of 6,7‐Benzotropolone Using Ring‐Closing Metathesis Variants, Which Circumvent a Strongly Acidic Hydrolysis in the Sequel

A Wittig reaction of 3-hydroxyphtalide (11) gave ortho-sty­rene-2-carboxylic acid (12). Its Weinreb amide 13 acylated heterosub­stituted methyllithiums. This led to aryl “methyl” ketones whose sp3-carbon was substituted by Cl + OMe (in 14a), 2 ´ 14b), OtBu 17a), SPh 17b) or SO2Ph 17c). The enolates these were C-allylated. furnished the benzene-fused octa-1,8-dienones 7a-b and 9a-c, respectively. Ring-closing meta­theses pro­vided corresponding benzocycloheptadienones 8a-b 10a-c. Their ke­tone moieties a,a-disubstituted 8a-b) a-monosub­stituted 10a-c). Each substitution pattern allowed generate hydroxy­enone motif benzocyclo­heptatrienone - 6,7-benzotropolone 6a: MeO- PhS-con­tain­ing benzo­cy­clohep­tadienone 8a 6,7-benztropo­lone methyl ether (15) sulf­oxide formation pyrolysis; 15 demethyl­ated with BCl3. same in­termediate resulted from dichloroben­zocy­cloheptadien­one 8b NaOMe. benzocyclo­heptadienone 10a de(tert-but­ylated) formic acid; a subse­quent Pfitzner-Moffatt oxidation com­pleted (6a) once more. PhS-containing ben­zocyclo­hep­tadienone 10b a-acetoxylated Pb(OAc)4; re­sulting O,S-acetal 6,7-ben­zotropolone hydrolysis. PhSO2-containing substrate 10c deprotonated where­upon an ox­idation Me3Si-O-O-SiMe3 6,7-benzotrop­olone (6a).