Selective Cu-Catalyzed Intramolecular Annulation of 3-Aryl/Heteryl-2-(diazoacetyl)-1H-pyrroles: Synthesis of Benzo/Furo/Thieno[e]-Fused 1H-Indol-7-oles and Their Transformations

Abstract

The Co­(III)-catalyzed reaction of 1,3-dicarbonyl compounds with 2-(diazoacetyl)-2H-azirines, prepared by a simplified procedure from 2H-azirin-2-carbonyl chlorides, led in high yields to the formation of 2-(diazoacetyl)­pyrroles, while leaving the diazoacetyl function intact. The intramolecular aromatic substitution reaction of 2-(diazoacetyl)­pyrroles, catalyzed by Cu­(OTf)2, provided selectively previously unknown benzo­[e]- and hetero­[e]-fused indol-7-oles in good yields. Formylation of benzo­[e]­indol-4-ol led selectively to the 5-formyl derivative, which is a good precursor for an unusual salen ligand and its Ni-complex. Triflates prepared from benzo­[e]­indol-4-oles gave various 4-substituted benzo­[e]­indoles carrying aryl, 2-thienyl, 2-pyridyl, and alkynyl groups, in excellent yields using cross-coupling reactions. 4-(2-Pyridyl)­benzo­[e]­indoles, upon treatment with BF3·Et2O/Et3N, afforded a new type of fluorescent boron complexes with large Stokes shifts.

Isomerization of 5-(2H-Azirin-2-yl)oxazoles: An Atom-Economic Approach to 4H-Pyrrolo[2,3-d]oxazoles

“…A series of 5-(2H-azirin-2-yl)oxazoles 2 was synthesized from 2-(3-aryl/heteroaryl)-2diazoacetyl-2H-azirines 1 [28] by Rh 2 (oct) 4 catalyzed reaction [27] with a set of substituted acetonitriles, benzonitriles, acrylonitrile and fumaronitrile in a 15-73% yield (Figure 1). Intramolecular ring-to-ring isomerization of azirines with the formation of fivemembered nitrogen heterocyles most often occurs under conditions of metal catalysis or thermolysis at high temperatures .…”

“…This is not least due to the difficulties in the synthesis of polyheteroatomic azoles bearing an azirin-2-yl substituent. One of the possible solutions to this problem could be the use of 2diazoacetylazirine building blocks 1, the convenient synthesis of which we have recently reported [27,28]. Preliminary results on the Rh(II)-catalyzed reaction of 2-diazoacetylazirines with acetonitrile demonstrated the principal utility of this protocol for the preparation of 5-(2H-azirin-2-yl)oxazoles 2 [27].…”

Non-natural 2H-azirine-2-carboxylic acids: an expedient synthesis and antimicrobial activity

“… 8,9 In particular, it has been demonstrated that 5-chloroisoxazoles can be transformed to 2 H -azirine-2-carbonyl chlorides under treatment with anhydrous FeCl 2 in acetonitrile. 10 …”

Recent Advancements in Pyrrole Synthesis

“…Various motifs of dicarbonyl compounds have been extensively utilized toward pyrrole synthesis. [83][84][85][86][87][88][89][90][91][92][93] As discussed in this section, this class of starting materials have enabled the development of a broad array of new synthetic reactions.…”