Furo indoles, preparation

Transition metal catalyzed decomposition of diazoester 64b, which is available from 64a with TsNj/base, results in the formation of furo[3,4-b]indole 65. This intermediate is trapped intramolecularly in situ to give 66. Furo[3,4-b]indoles of type 67 can be prepared similarly... 

Furthermore, the Wu group [141] has prepared isoquinolines and iso-indoles starting from 2-(2-phenylethynyl)-benzonitrile, while Yamamoto and coworkers [142] prepared benzopyrans from alkynylbenzaldehydes, the Cacchi group [143] synthesized benzofurans, and Balme and coworkers [144] furo[2,3-fo]pyridones. 

The pyrido[3, 4 4,5]furo[3,2-A]indole 24 can be prepared by Curtius rearrangement of 3-[5-(2-nitrophenyl)-2-furyl]-propenoic azide 25, followed by reduction of the nitrophenyl functionality of the product 26, chlorination of the tetracyclic product (PCI5), then reduction (Zn/AcOH) to give the parent compound 24 <1987CCC192> (Scheme 7). 

Miki and Hachiken reported a total synthesis of murrayaquinone A (107) using 4-benzyl-l-ferf-butyldimethylsiloxy-4fT-furo[3,4-f>]indole (854) as an indolo-2,3-quinodimethane equivalent for the Diels-Alder reaction with methyl acrylate (624). 4-Benzyl-3,4-dihydro-lfT-furo[3,4-f>]indol-l-one (853), the precursor for the 4H-furo[3,4-f>]indole (854), was prepared in five steps and 30% overall yield starting from dimethyl indole-2,3-dicarboxylate (851). Alkaline hydrolysis of 851 followed by N-benzylation of the dicarboxylic acid with benzyl bromide and sodium hydride in DMF, and treatment of the corresponding l-benzylindole-2,3-dicarboxylic acid with trifluoroacetic anhydride (TFAA) gave the anhydride 852. Reduction of 852 with sodium borohydride, followed by lactonization of the intermediate 2-hydroxy-methylindole-3-carboxylic acid with l-methyl-2-chloropyridinium iodide, led to the lactone 853. The lactone 853 was transformed to 4-benzyl-l-ferf-butyldimethylsiloxy-4H-furo[3,4- 7]indole 854 by a base-induced silylation. Without isolation, the... 

A structurally novel series of substituted 10//-benzo[4,5]furo[3,2- ]indole-l-carboxylic acids 504-507 was prepared and shown to possess potent, bladder-selective smooth muscle relaxant properties and thus is potentially useful for the treatment of urge urinary incontinence. Electrophysiological studies using rat detrusor myocytes have demonstrated that prototype compound 8 produces a significant increase in hyperpolarizing current, which is iberiotoxin (IbTx)-reversed, thus consistent with activation of the large-conductance Ca -activated potassium channel (BKca) <2001BML2093>. 

Furo[3,4-h]indoles have also been prepared as transients for inter- and intramolecular Diels-Alder reactions (96JOC6166) (see Section IV). 

Mixed Systems.—4H-Furo[3,2-6]indole (769), the parent of a new ring system, has been prepared by heating 2-o-azidophenylfuran 2-o-azidophenyl-... 

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