9-substituted xanthene synthesis

The advantages of this method are the ease of modification of each unit and their combination with other pharmacophores as potential pharmacological agents. This transformation could be of immense importance to medicinal chemists using appropriate templates to generate a hbrary of substituted xanthenes. It is proved to be a diversity-oriented protocol for the synthesis of pharmaceutically important molecules like coumarins, chalcones, Schiff base, aiylcoumarins, and dioxocine analogs. 

C. Lu, A.V. Dubrovskiy, R.C. Larock, Synthesis of 9-substituted xanthenes by the condeiwation of ar)mes with orffto-hydroxychalcones. Tetrahedron Lett 53 (2012) 2202-2205. 

The microwave irradiation tool has been widely utilized to promote organic transformations. An iron-catalyzed, microwave-promoted method reported by Li and coworkers for the synthesis of 9-substituted xanthenes has been developed... 

Scheme 9.27 Microwave-Promoted Synthesis of 9-Substituted Xanthenes.

The reaction of methoxy-substituted 1,4-dihydroatomatic systems is a general one. Other condensed systems react ia a similar manner, for example, 3,6-dimethoxy-1,4,S,8-tetrahydronaphtha1ene and derivatives of anthracene (35) and xanthene (36) (74). The proposed method enables synthesis of the tri-and tetracarbocyanines where the whole chromophore is iategrated iato a rigidizing skeleton. Asymmetrical polymethines can also be obtained similarly. 

Meisenbach M, Echner H, Voelter W. New methoxy-substituted 9-phenyl-xanthen-9-ylamine linkers for the solid phase phase synthesis of protected peptide amides. Chem Commun (Cambridge) 1997 849-850. 

Modulated acid lability of protecting groups is extremely important in ribonu-cleoside synthesis. A comparison of the relative rates of hydrolysis of a some diarylmethylene protecting groups for the 2 3 -cu-diol system of uridine shows that aryl substitution achieves much greater add lability than the conventional isopropylidene group. Comparison of the half-times for the hydrolysis of the di-(p-anisyl)methylene (B), xanthen-9-ylidene (C) and 2,7-dimethylxanthen-9-yli-dene (D) acetals in trifluoroacetic acid/water/methanol (1 2 7 v ) at 30 revealed that the 2J-dimethylxanthen-9-ylidene system is 20 times more labile than the isopropylidene acetal. 

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