534. The reaction between o-hydroxy-aldehydes and diphenylethylenes

Facile syntheses of 2H‐chromenes or 9‐functionalized phenanthrenes under mild conditions in moderate to good yields have been developed. They each involve annulations of arynes with α,β‐unsaturated compounds bearing different electron‐withdrawing groups (EWGs). Depending on the natures of the different EWGs, the reactions proceed by different pathways: enals react with arynes through a tandem [2+2] cycloaddition/thermal electrocyclic ring‐opening/6e‐electrocyclization sequence to afford 2H‐chromenes, whereas acyl‐/ethoxycarbonyl‐/cyano‐substituted styrenes undergo Diels–Alder reactions with arynes followed by aromatization to afford 9‐functionalized phenanthrenes. The scope, limitations, regioselectivities and mechanisms have been studied and are discussed in detail.

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The reactions of salicylaldehydes and 2,2‐diary 1‐2H‐chromenes with 1,1‐bis[p‐(dimethylamino)phenyl] ethylene; photochromic chromenes

Zwanenburg

Maas

1975

Recl. Trav. Chim. Pays‐Bas

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The reactions between 1,1‐bis(p‐dimethylaminophenyl)ethylene (Michler's ethylene) (5) and salicylaldehydes (6) were studied for the purpose of synthesizing photochromic chromenes (1). Although we proved the presence of the chromene 1 under some conditions, the only compounds we could isolate were the so‐called “disubstitution products” 7. Reaction of 2,2‐bis[p‐(dimethylamino)‐phenyl]‐2H‐chromene [1a, synthesized by a Grignard reaction of coumarin with p‐(dimethylamino)‐phenylmagnesium bromide] with Michler's ethylene also gives the “disubstitution product” 7a. Reactions of Michler's ethylene with 2,2‐bis(p‐methoxyphenyl)‐2H‐chromene (3) and the spiropyran 11 furnished the “mixed disubstitution products” 9 and 10, respectively. A reaction of the latter with 5‐nitrosalicylaldehyde gives 2,2‐bis[p‐(dimethylamino)phenyl]‐6‐nitro‐2H‐chromene 1b. The photochromism of the synthesized chromenes is described briefly.

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534. The reaction between o-hydroxy-aldehydes and diphenylethylenes

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Alkoxychromans

Alkoxychromans

A Facile Synthesis of 2H‐Chromenes and 9‐Functionalized Phenanthrenes through Reactions between α,β‐Unsaturated Compounds and Arynes

The reactions of salicylaldehydes and 2,2‐diary 1‐2H‐chromenes with 1,1‐bis[p‐(dimethylamino)phenyl] ethylene; photochromic chromenes

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