A Novel Route to the Dibenzofuran Ring System: Possible Applications as a Rigid Thyroid Hormone Template.

Photochemical cyclization reactions of iodinated diphenyl ethers to produce dibenzofuran derivatives have been studied. While U.V. irradiation of the thyroid hormone thyroxine produces a complex mixture of products, treatment of the thyroid hormone analogue 3,5-diiodo-4-(4'-methyoxphenoxy)nitrobenzene with U.V. light yielded 4-iodo-8-methoxy-2-nitrodibenzofuran (34%) in a clean reaction. The functionalized dibenzofuran framework produced in this reaction has considerable potential for the development of novel, rigid thyroid hormone analogues.