N-Heterocyclic carbene-catalysed homoenolate addition reaction to 3-cyano-2-imino-2H-chromenes: synthesis of C4-functionalized 2-amino-3-cyano-4H-chromene

A NHC-catalyzed homoenolate addition reaction between enals and iminochromenes to yields of a new type of C4-functionalized 2-amino-4H-chromenes has been developed.

A rhodium-catalysed conjugate addition/cyclization cascade for the asymmetric synthesis of 2-amino-4H-chromenes

The enantioselective synthesis of 2-amino-4H-chromenes via the cascade rhodium-catalysed conjugate addition/hetero Thorpe-Ziegler reaction is reported. Moderate to good yields (up to 98%) and high enantioselectivities (up to 92% ee) were obtained with a chiral diene-coordinated rhodium complex as the catalyst. This protocol remedies the methodological deficiency in the asymmetric synthesis of 4-aryl 2-amino-4H-chromenes.

Mn-mediated sequential three-component domino Knoevenagel/cyclization/Michael addition/oxidative cyclization reaction towards annulated imidazo[1,2-a]pyridines

The sequential three-component reaction between o-hydroxybenzaldehydes, N-(cyanomethyl)pyridinium salts and a nucleophile towards substituted chromenoimidazopyridines under oxidative conditions has been developed. The employment of Mn(OAc)₃·2H₂O or KMnO₄ as stoichiometric oxidants allowed the use of a wide range of nucleophiles, such as nitromethane, (aza)indoles, pyrroles, phenols, pyrazole, indazole and diethyl malonate. The formation of the target compounds presumably proceeds through a domino Knoevenagel/cyclization/Michael addition/oxidative cyclization reaction sequence.

Enantioselective vinylogous Michael addition of β,γ-unsaturated butenolide to 2-iminochromenes

An efficient organocatalyzed asymmetric synthesis of 2-amino-4H-(2-furanone)-3-carbonitrile via vinylogous Michael addition of non-activated β,γ-unsaturated butenolide to 2-iminochromenes has been realized.

Enantioselective Synthesis of New Dimeric Chromene Derivatives by a Ferrocene-Copper Catalyst System

Novel 2-iminochromene dimers were prepared in excellent yields (93–99%) and with high to excellent enantioselectivities (89–97% ee) by a simple and efficient method. The precursor 2-[(3-cyano-2H-chromen-2-ylidene)amino]acetates and both racemic and enantioselective 2-iminochromene dimers were disclosed and characterised for the first time.

K2CO3-mediated synthesis of functionalised 4-substituted-2-amino-3-cyano-4H-chromenes via Michael-cyclization reactions

An efficient approach for the synthesis of functionalized 4-substituted-2-amino-3-cyano-4H-chromenes moderate to high yields (up to 98%) has been achieved via a tandem K2CO3 catalyzed conjugate addition-cyclization reaction of malononitrile and a range of Knoevenagel adducts previously formed from oxindole, pyrazolone, nitromethane, N,N-dimethylbarbituric acid or indanedione. This methodology differs from the previous classical methods in its simplicity and ready availability of the catalyst.