Photochromic bi-naphthopyrans

A series of novel 3-aryl-(3,3-diaryl-3H-naphtho[2,1-b]pyran-8-yl)-3H-naphtho[2,1-b]pyrans has been accessed from 6-bromo-2-naphthol via a four step transformation. Acylation of the dianion derived from the treatment of 6-bromo-2-naphthol with n-butyllithium with Weinreb amides and subsequent reaction with a 1,1,-diarylprop-2-yn-1-ol gave 8-aroyl-3H-naphtho[2,1-b]pyrans in good yield. Addition of lithium trimethylsilylacetylide to the foregoing 8-aroylnaphthopyrans proceeded smoothly with base mediated desilyation to afford the target bi-naphthopyrans upon acid-catalysed reaction with 2-
naphthol. Preliminary evaluation of the photochromic response of the new bi-naphthopyrans revealed reversible independent naphthopyran ring-opening leading to a complex photochromic signature.