LE3 .A278 2021

2021

Jha, Amitabh

Acadia University

Master of Science

Masters

Chemistry

Chemistry

Petasis reaction is a multicomponent reaction that involves the reaction of an amine, a carbonyl compound, and a boronic acid to form substituted amines. We envisioned that the nucleophilic amine reactant can be replaced with a nucleophilic phenol in the Petasis reaction to produce substituted benzoxanthenes after intramolecular cyclodehydration. Benzoxanthenes are important biologically active heterocycles. The reaction of -naphthol, salicylaldehyde, and phenyl boronic acid in the presence of a Lewis acid catalyst Cu(OTf)2 under microwave heating conditions (150 [degree] C, 10 min) in DMF as the solvent afforded the desired substituted benzoxanthene, 12-phenyl-12H-benzo[a]xanthene, in 40% yield. However, in the process of method development, the same reaction under microwave heating conditions (170 [degree]C, 20 min) afforded 12H-benzo[a]xanthene (unsubstituted at position 12) in 25% yield when carried out without the Lewis acid catalyst. This unexpected product does not contain the phenyl group which is derived from the phenyl boronic acid. If the phenyl boronic acid did not participate in the reaction, the reaction of -naphthol and salicylaldehyde should have, mechanistically, afforded 12H-benzo[a]xanthen-12-ol that contains a benzylic -OH group. Moreover, the product was not obtained if phenyl boronic acid was not used. Thus, somehow the benzylic -OH appeared to have been reduced in presence of phenyl boronic acid. This was intriguing as no reductant was used in the reaction. An exploratory reaction showed that phenyl boronic acid catalyses in the reduction of triphenylmethanol (a model benzylic alcohol) to triphenylmethane. The reaction of triphenylmethanol with phenyl boronic acid in DMF under microwave heating conditions (170 C, 20 min) afforded triphenylmethane in 71% yield. Furthermore, deuterium-labeled reactions showed that the “H” on triphenylmethane was provided by the solvent DMF. Several analogs of both the substituted and unsubstituted benzoxanthenes were prepared and characterized by the two novel processes developed in this investigation.

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https://scholar.acadiau.ca/islandora/object/theses:3682