ABSTRACT
The tandem hydroformylation-Fischer indolisation protocol is used in the synthesis of 2,3-disubstituted indoles. After hydroformylation of selected olefins to form alpha-branched aldehydes in a one-pot procedure these are condensed with phenylhydrazine to give hydrazones. Upon acid-promoted [3,3]-sigmatropic rearrangement indolenine intermediates with quaternary centres in the 3-position are formed, which, after selective Wagner-Meerwein-type rearrangement of one of the substituents from the 3- to the 2-position, lead to 2,3-disubstituted indoles. Several olefins, bearing substituents with various functional groups, as well as cyclic olefinic systems are investigated.
Subject(s)
Indoles/chemical synthesis , Aldehydes/chemistry , Alkenes/chemistry , Hydrazines/chemistry , Hydrazones/chemistry , Phenylhydrazines/chemistryABSTRACT
[reaction: see text] A novel one-pot synthesis of indole systems via tandem hydroformylation/Fischer indole synthesis starting from olefins and arylhydrazines is described. This tandem procedure leads directly to 3-substituted indoles if unsubstituted phenylhydrazine is used and to 3,5- respectively 3,7-disubstituted indoles if para- or ortho-substituted arylhydrazines are used.
