Synthesis of New Thiophene‐Substituted 3,3‐Diphenyl‐3H‐naphtho[2,1‐b]pyrans by Cross‐Coupling Reactions, Precursors of Photomodulated Materials
3,3-Diphenyl-3H-naphtho[2,1-b]pyrans linked to one, two, or three thiophene nuclei in different positions of the naphthalene moiety (5, 6, 8, and 9) by a covalent bond have been prepared in good yields. A Suzuki cross-coupling reaction was used with two possible strategies: chromenization before the coupling with oligothiophenes or chromenization after the coupling, the main intermediates being the diphenyl propargylic alcohol, the functionalized naphthol derivatives, and the thiophenic boronates. The overall yields for obtaining such photochromic compounds are generally quite satisfying. For the 7-position, the coupling reaction has been realized using a Grignard reaction between a tetralone derivative and a thiophenic bromo magnesium intermediate. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)