One-Pot Synthesis of Naphthalenes from Baylis-Hillman Adducts via Pd-Mediated Successive Allylation and Arylation

Abstract

Introduction of nucleophiles at the primary position of Baylis-Hillman adducts has been carried out by the nucleophilic substitution reaction from the acetate or primary bromide derivative of Baylis-Hillman adduct. Palladiumassisted introduction of nucleophiles has also been reported in the Baylis-Hillman chemistry via the corresponding πallylpalladium intermediate. Thus we reasoned that one-pot synthesis of dihydronaphthalene could be carried out by Pd-mediated successive allylation and arylation protocol from the reaction of 1a, the acetate of Baylis-Hillman adduct of 2-bromobenzaldehyde, and dimethyl malonate (2a) as in Scheme 1. The reaction between 1a and 2a produced naphthalene derivative 5a (73%) in a one-pot, under the influence of Pd(OAc)2/TBAB/ K2CO3 in DMF at 90 C (3 h), instead of the expected dihydronaphthalene 4a. The reaction mechanism for the one-pot formation of 5a can be postulated as the following successive processes: (i) allylation of 2a via the π-allylpalladium intermediate (I) to produce the substitution product 3a, (ii) Pd-mediated arylation of 3a to dihydronaphthalene 4a via the intermediate (II), and (iii) dealkoxycarbonylation and concomitant aerobic oxidation process to give the final product 5a. In order to clarify the last step of the concomitant dealkoxycarbonylation and aerobic oxidation, we examined the reaction in more detail as in Scheme 2. The reaction of compound 3a, prepared by nucleophilic substitution reaction from 1a and 2a (K2CO3, CH3CN, rt, 3 h, 78%), 1,7,9