Indoles polycyclic heterocycles containing

Since the publication of CHEC-II(1996) <1996CHEC-II(6)1>, in which thermally induced [4+2] cycloadditions have been reviewed, significant progress has been realized in this strategy, especially for the synthesis of polycyclic heterocycles. Cyclophanes 12 containing pyridazine and indole units were used for the synthesis of pentacyclic compounds 13 via a thermally induced transannular inverse-electron-demand Diels-Alder reaction (Equation 2) <20020L127, 2002AGE3261>. 

Indolizines, indolizidines, indoles, and other bicyclic or polycyclic compounds containing a fused pyrrole or pyrrolidine moiety often possess potent and useful biological activities. There have been several approaches to the preparation of fluorinated analogues of these heterocycles, mainly based on 1,3-dipolar addition reactions using fluorinated synthons either as the dipole or as the dipolarophile. Several examples of this strategy are given below. 

Nitrogen-containing heterocycles are also available via intramolecular hetero Diels-Alder reactions. Williams employed an aza diene to prepare a complex polycyclic synthetic intermediate in his synthesis of versicolamide B. Boger reported a tandem intramolecular hetero Diels-Alder/l,3-dipolar cycloaddition sequence for the synthesis of vindorosine. Cycloaddition precursor 137 undergoes an inverse electron demand Diels-Alder reaction to yield 138. This compound decomposes via a retro dipolar cycloaddition to generate nitrogen gas and a 1,3-dipole that completes the cascade by reacting with the indole alkene to afford 139. Seven more steps enable the completion of vindorosine. ... 

Other kinds of molecules besides benzene-like compounds can also be aromatic. The cyclopentadienyl anion and cycloheptatrienyl cation, for instance, are aromatic ions. Pyridine and pyrimidine are srx-memhered, nitrogen-containing, aromatic heterocycles. Pyrrole and imidazole are five-membered, nitrogen-containing heterocycles. Naphthalene, quinoline, indole, and many others are polycyclic aromatic compounds. 

Among the many biological molecules that contain polycyclic aromatic rings, the amino acid tryptophan contains an indole ring and the antimalarial dmg quinine contains a quinoline ring. Adenine and guanine, two of the five heterocyclic amine bases found in nucleic acids, have rings based on purine. 

Larocket fl/. in 2000 developed the fluoren-9-one synthesis by the cyclocarbonyla-tion of ort/zo-halobiarys with a commercially available Pd(PCy3)2 catalyst [17] This procedure was initiated by the palladium(0) and could be utilized to the synthesis of polycyclic and heterocyclic fluorenones containing the fused isoquinoline, indole, pyrrole, thiophene, benzothiophene, and benzofuran rings (Table 15.12). 

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