Organic Chemistry

Efficient Synthesis and Functionalization of 3-Bromo Naphtho[2,3b]thiophene



Naphtho[2,3b]thiophene is a linear sulfur containing polycyclic aromatic hydrocarbon. Naphtho[2,3b]thiophene and its derivatives are commonly accessed by a Bradsher cyclization. Synthesis of the Bradsher cyclization substrate typically requires harsh conditions, including several oxidation state changes. Here we report an improved, multigram synthesis of 3-bromonaphtho[2,3b]thiophene, exploiting a copper-catalyzed cross coupling to prepare the Bradsher substrate in 3 steps from commercial materials while minimizing redox reactions. Modification of the naphthothiophene scaffold in the 3-position has not previously been reported. In this work, the 3-bromonaphthothiophene is further functionalized via lithium-halogen exchange, with the key finding being a specific order of addition in lithiation is required to avoid undesired rearrangement reactions. A small yet versatile set of derivatives, including a naphthothiophene-containing chiral amine are prepared.


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Supplementary material

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Supporting Information
Experimental Procedures, X-Ray Data, NMR Data