Synthesis of a new photochromic 2,2-diphenylpyrano[3,2-h]quinoline

The formation of new materials based on the bistable structures consisting of light-sensitive fragments tightly bonded to complex-forming centers of molecules is one of the priority areas at the junction of organic, coordination chemistry, and photochemistry. 2 H-Pyrano[3,2-h]quinoline diaryl derivatives are the examples of such compounds, the structure contains a coordination node formed by nitrogen atom of the quinoline ring and the oxygen atom of the annelated pyran heterocycle, which is a potential photochromic fragment of the 2H-chromene part of the molecules. In agreement with the literature data [1-5], photochromic derivatives of pyrano[3,2-h]quinoline are known, but they are spirocyclic compounds which contain indole as hetarene, however the pyrrole nitrogen affects the distribution of the electron density in the molecule substantially changing its properties. The basicity of this heteroatom is an important factor, which may effect the study of complex formation and its influence on the photochromic processes. Calculations [6] of an example of 2H-pyrano[3,2-h]quinoline containing a hydrogen atom at position 2 showed that changes in the magnetic properties of metal chelates under the influence of photoinduced cis-trans rearrangement makes it relevant to complex use the properties of these compounds and opens up opportunities to create controlled photomagnets. There are known methods for the synthesis of 2H-chromene derivatives containing annelated five- and six-membered heterocycles that use hydroxygroups of the corresponding heteroannelated phenols in reaction with diarylpropargyl alcohols [7-9]. We have attempted the synthesis of 2,2-diphenylpyrano[3,2-h]quinoline (3) from the reaction of 8-hydroxyquinoline (1) with 1,1-diphenyl-2-propyn-1-ol under the conditions described above, however the reaction products were the adducts of 8-hydroxyquinoline either with propargyl alcohol (2) formed under the influence of the medium, or directly with the catalyst itself.