Formal 2+2+2 photoredox synthesis of naphthalene derivatives using aniline as traceless directing group.

by Wang, Qile; Zheng, Nan

Naphthalenes are an important class of structural motif which widely exists in natural product and functional materials. Because of the importance of naphthalene structure, synthetic routes that is based on coupling with alkyne as most commonly used and straight forward method including annulation, cyclioaddn. and rearrangement towards substituted naphthalenes are developed recently. However, there still are two main challenges for regiospecific synthesis of substituted naphthalene while coupling with alkyne, namely regioselectivity and functionality tolerance. To overcome this hurdle, we have develop a regioselective method under mild condition and as a result, a broad scope of functional groups are tolerated including ketone, halide, diynes and saccharide. We highlight the power of our new approach to access substituted naphthalenes by [2+2+2] fashion under mild condition. Benzocyclobutenes are recently reported to undergo annulation to form naphthalenes initiated by ring-opening process which is mediated by transition metal, high temperature or molar equivalent usage of oxidant. We modify the benzocyclobutenes motif with aniline which can undergo radical ring-opening process mediated by visible light through a redox neutral mechanism. Taking advantage of this mild condition and the feature of radical chem., excellent regioselectivity and broad functional group tolerance were achieved while coupling with alkyne. More importantly, aniline can be eliminated during aromatization leaving no unwanted or unnecessary functionalities which could be troublesome to remove.