Zinc chloride-acetic anhydride, rearrangements

Zinc chloride/acetic anhydride Rearrangement of ethylenecarhohydrates... 

Rearrangement with Zinc Chloride-Acetic Anhydride. 192... 

Zimmerman 103) applied the well known rearrangement of 4,4-disubstituted cyclohexa-2,5-dienones (e.g. the 4,4-diphenyl derivative tives the 3,4-disubstituted phenols l)). Using acetic anhydride and a small amount of concentrated sulfuric acid, 97.5 % of 3,4-diphenylphenolacetate is formed, which in turn is hydrolyzed to give 3,4-diphenylphenol. This is one of the easiest synthesis of this phenol. 2-Bromo-4,4-diphenylcyclohexa-2,5-dienone rearranges by a similar route to give a 49 % yield of 2-bromo-3,4-diphenylphenolacetate and 47 %2-bromo-4,5-diphenylphenolacetate U4). A [1.2]-phenyl shift of 4-methoxy-2,3,4,6-tetraphenyl-2,5-dienone in acetic anhydride and zinc chloride gives rise to 4-methoxy-2,3,5,6-tetraphenylacetate (m.p. 284 °C, 85% yield)115 . 

Similar rearranged products can be seen in the Clemmensen reduction of many cyclic and acyclic compounds carrying the 1,3-diketone system. The intermediacy of a cyclopropanediol derivative was established by Curphey et al., who showed that the cyclopropane diacetate (19) can be obtained in high yield by reaction of (18) with zinc dust in acetic anhydride and hydrogen chloride, as well as by electrolysis. The diketone (18) gives a mixture of rearranged products (20 and 21) under normal Clemmensen... 

Reactions involving both Ca, C/i, and Cy relative to a cyclopropane ring can formally be classified as ene reactions, 1,3-sigmatropic rearrangements, and Sn2 substitutions. An ene reaction occurred on reaction of A-sulfinylbenzenesulfonamide with bicyclo[4.1.0]hept-3-ene 1 under mild conditions to give 2 in good yield. " Terpene 1 underwent a similar reaction on treatment with acetic anhydride in the presence of zinc(II) chloride. Compound 2 is... 

A side-chain methylenamino group reacts with a nitroso group (introduced in situ) when the compound is heated with mineral acid [2466]. An unusual reaction occurred when the nitro-t-amine (103.4) was refluxed with acetic anhydride and zinc chloride the course of this reaction may involve an A -oxide [2039]. When an o-nitroalkylamine is heated with ethoxide, the two functions are converted into a 1-hydroxyimidazole ring [3004]. Nitrosation of the pyrim-idinone (103.5) involves several steps including a Fischer-Hepp rearrangement of an iV-nitroso to a ring-C-nitroso the final product is a 6-(4 -nitrophenyl-amino)purin-2-one [2667]. In a weakly basic medium, the nitroamine (103.6) is cyclized to either the benzimidazole (when R == H), or the benzimidazolone (when R H). 

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