Synthesis of novel photochromic pyrans via palladium-mediated reactions

Abstract

SummaryPhotochromic pyrans for applications in material and life sciences were synthesized via palladium-mediated cyanation, carbonylation and Sonogashira cross-coupling starting from bromo-substituted naphthopyran 1 and benzopyrans 2a/b. A novel photoswitchable benzopyran-based ω-amino acid 6 for Fmoc-based solid-phase peptide synthesis is presented. The photochromic behaviour of the 3-cyano-substituted benzopyran 5a was investigated by time-resolved absorption spectroscopy in the picosecond time domain.

Opening 2,2-diphenyl-2H-chromene to infrared light

“…13 The excited-state dynamics of compounds related to 2,2-diphenyl-2H-chromene have been extensively investigated using transient absorption spectroscopy. [12][13][14][15][16][17] Such studies have practically all been performed in the visible spectral region because the absorption spectra of the closed and open isomers are quite different and thus easily distinguishable. 1 At the same time, it is also recognised that some of the hypothesised intermediates and final photoisomers (vide infra), and in particular the various open forms, have very similar absorption spectra and only differ in their oscillator strengths.…”

The photochemical ring opening reaction of chromene as seen by transient absorption and fluorescence spectroscopy

“…These compounds were investigated in different solvents ( polar vs. non-polar) 13 and for different excitation conditions, (S 1 vs. S N excitation) 19 using continuous-wave spectroscopy 12,13,15,22,23 or timeresolved techniques, e.g., transient absorption, TA. 14,[18][19][20]24,25 Based on the data from transient absorption measurements and the spectral dynamics observed after photoexcitation, at first a sequential model with fast excited state decay was suggested for the ring-opening reaction (Fig. 1a).…”

Base-Mediated Ring-Contraction of Pyran Systems Promoted by Palladium and Phase-Transfer Catalysis

“…Failed Pd-mediated cyanation of 2-bromonaphthopyran 19 An undesirable ring-contraction of the 3H-naphtho [2,1-b]pyran 19 to afford the naphtho [2,1b]furan 20 in 65% yield was observed instead of the postulated palladium-catalysed cyanation reaction (Scheme 6). 25 Given the predisposition of the pyran unit to contract under a variety of reaction conditions, especially including in the presence of base and palladium, this present study aims to understand the ring-contraction mechanism of naphthopyrans. Furthermore, our investigations have revealed two efficient and robust ring-contraction protocols which have been successfully applied to the preparation of naphthofurans, naphthodifurans and a benzindole.…”