Indole-2-carboxaldehydes

Indole-2,3-quinodimethanes have also been exploited as the key intermediates in indolo[2,3-a]caibazole synthesis, allowing the preparation of several interesting systems. Thus, when the starting materials 74a-b (obtained from the condensation of protected indole-2-carboxaldehydes with 2-aminostyrene) underwent treatment with methyl chloroformate in hot chlorobenzene, the carbamates 75a-b were obtained, and could subsequently be dehydrogenated into the aromatic compounds 76a-b (Scheme 11). However, all functionalization attempts of the methyl... 

The quinoline 88 has been transformed into the intermediate 89, which was subsequently ring-opened by ozonolysis, followed by base-induced ring closure to the indole-2-carboxaldehyde 90 (Scheme 60) <2002TL5295>. Several useful 4-substituted indoles have also been prepared by ring-contraction of A-alkyl-5-aminoisoquinolinium salts with the system NaHS03/Na2S03 <2000JHC1293, CHEC-III(3.0340)333>. 

Decarbonylation decarboxylation. At 110-170° this complex in catalytic amounts effects decarbonylation of simple aldehydes in quantitative yield.- Decarbonylation of typical indole-2-carboxaldehydes with in j/ M-generated catalyst proceeds in 82-95% yield. In fact, decarboxylation of some indole-2-carboxylic acids can be effected in higher overall yield by conversion to the aldehyde (LiAlH4 MnO,) followed by decarbonylation than by copp)er-catalyzed decarboxylation. ... 

H- or 4-alkylfuro[3,2-6]indole-2-carboxaldehydes (346-349) have been obtained by Vilsmeier formylation of the corresponding furo[3,2-Z)]indoles (342-345) (Equation (8)) <77JHC975>. 

An annulation of indole-2-carboxaldehyde to 3-carboethoxy-P -carboline was accomplished by using reductive amination to install a side chain with a -acetal functionality. Cyclization occurred on reaction with TiCl,. <94T6299> Methyl 4-methyl-p -carboline-3-carboxylate was prepared by a similar protocol. 

The synthesis of l,2-cyclopropapyrrolo[l,2-a]indoles devised by Moody and Jones [54] was based on 1,3-dipolar addition of a diazo group to an alkene (Scheme 24). In this synthesis, indole-2-carboxaldehyde 169 was alkylated with allyl bromide in the presence of sodium hydride and then condensed with tosylhydrazine to give 170. The sodium salt of 170 underwent [3 + 2] cycloaddition, affording 171, when it was heated in benzene. Further heating in refluxing... 

New synthetic methods for benzodiazepine synthesis involving Ugi-type multicomponent/post-Ugi cyclization reactions continue to be of interest. Ugi reactions of indole-2-carboxaldehydes, isocyanides, amines, and 2-iodobenzoic acid derivatives led to intermediates which, with copper(I) catalysis, underwent intramolecular indole N-arylation to produce indolo-fused benzodiazepinones, such as 134 (13CC2894). 2-Azido-benzaldehyde, isocyanides, propargylamines, and nitrophenols underwent Ugi-type reaction, Smiles-type rearrangement, and intramolecular azide-alkyne cyclization to afford triazolo-fused benzodiazepinones such as 135... 

In their total synthesis of (+)-isatisine A, Kerr and Karadeolian utilized a [3+2]-cycloaddition strategy to the tetrahydrofuran (Scheme 27) [27]. The cycloaddition between indole-2-carboxaldehyde 99 and vinylcyclopropane 100 was carried out... 

The synthesis of isatisine A113 started with the formation of the tetrahydroftiran ring through a Lewis acid-catalyzed cycloaddition reaction of the chiral (5)-vinyl cyclopropane diester 23 and iV-tosyl-indole-2-carboxaldehyde 24 (Scheme 10.42) [40]. 

---