Naphthalene → 2-Chloronaphthalene

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Microwave irradiation of styrene 5 in either 1,2-dichloroethane (DCE) at 180° C. for 30 min or 1,1,1-trifluorotoluene at 180° C. for 180 minutes afforded the cyclopenta-naphthalene derivative 6 in nearly quantitative yield with no additional purification required of the final product (entries 1 and 2, Table 1). With conditions for an efficient and high yielding IMDA reaction utilizing a lower boiling solvent in hand, scope and limitations investigations were initiated. First, substitution on the aryl group was examined; exchanging a hydrogen atom for a chlorine atom was deemed valuable, enabling access to a wide-range of naphthalene derivatives via palladium-catalyzed cross coupling reactions. Moreover, a chlorine atom is more stable and accessible than other halides or groups used for coupling, such as triflates. Styrenyl derivatives 5b, 5c, and 5d were prepared and subjected to microwave irradiation. The para-chlorostyrene 5b gave 7-chloronaphthalene 6b in quantitative yield after 200 min (entry 3). The ortho-chlorostyrene 5c also produced only one product, the 5-chloronaphthalene 6c in 86% yield, even though two products are possible (entry 4). The meta-chlorostyrene 5d gave an inseparable 1.4:1 mixture of the 6-chloro- and 8-chloronaphthalenes, 6d and 6d′ in 79% yield (entry 5).

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