Synthesis of Cyclohepta[b]indoles and Furo[3,4-b]carbazoles from Indoles, Tertiary Propargylic Alcohols, and Activated Alkynes.

A robust metal-free and environmentally friendly approach to cyclohepta[b]indole and furo[3,4-b]carbazole frameworks via a three-component reaction from indoles, tertiary propargylic alcohols, and activated alkynes is described. A probable mechanism was proposed on the basis of the isolation and characterization of a key intermediate of the reaction. A gram-scale reaction and product derivatizations were also performed to demonstrate the practicality of the developed methodology.

Synthesis of pyrano[3,2-c]quinolones and furo[3,2-c]quinolones via acid-catalyzed tandem reaction of 4-hydroxy-1-methylquinolin-2(1H)-one and propargylic alcohols.

Two acid-catalyzed tandem reactions between 4-hydroxy-1-methylquinolin-2(1H)-one and propargylic alcohols are described. Depending mainly on the propargylic alcohol used, these tandem reactions proceed via either a Friedel-Crafts-type allenylation followed by 6-endo-dig cyclization sequence to form pyrano[3,2-c]quinolones or a Friedel-Crafts-type alkylation and 5-exo-dig ring closure sequence to afford furo[3,2-c]quinolones in moderate-to-high yields. The pyrano[3,2-c]quinolones products could be further transformed to tetracyclic 4,9-dihydro-5H-cyclopenta[lmn]phenanthridin-5-one derivatives.

Synthesis of tetrahydro-ß-carbolines from 2-indolylmethyl azides and propargylic alcohols.

A facile and efficient route to tetrahydro-ß-carbolines from 2-indolylmethyl azides and propargylic alcohols via acid-catalyzed dehydrative annulation reactions is described. This reaction proceeds through a cascade sequence of Friedel-Crafts-type alkylation followed by intramolecular "Click" reaction, involving the formation of multiple chemical bonds in a single operation with excellent atom-economy and broad functional group tolerance.