Ortho-Quinone methides as key intermediates in cascade heterocyclizations

Development of new methods of heterocyclic synthesis is still a topical issue. In this connection, the trend related to the use of highly reactive o-quinone methides for the synthesis and functionalization of heterocycles appears rather promising. Since most of o-quinone methides are unstable, the choice of precursors and generation conditions is highly important for subsequent transformations involving them. Various methods of generation of o-quinone methides and cascade hetero- cyclizations in which the formation of these compounds is a key step are surveyed in the review. The trends of using o-quinone methides in the synthesis of various heterocycles are analyzed and the heterocyclization reactions involving these compounds are classified. © 2017 Russian Academy of Sciences and Turpion Ltd

Ortho-Quinone methides as key intermediates in cascade heterocyclizations

Development of new methods of heterocyclic synthesis is still a topical issue. In this connection, the trend related to the use of highly reactive o-quinone methides for the synthesis and functionalization of heterocycles appears rather promising. Since most of o-quinone methides are unstable, the choice of precursors and generation conditions is highly important for subsequent transformations involving them. Various methods of generation of o-quinone methides and cascade hetero- cyclizations in which the formation of these compounds is a key step are surveyed in the review. The trends of using o-quinone methides in the synthesis of various heterocycles are analyzed and the heterocyclization reactions involving these compounds are classified. © 2017 Russian Academy of Sciences and Turpion Ltd

Reaction of trifluoroacetylchromenes with 6-aminouracils. Synthesis of pyrido[2,3-d]pyrimidines

The condensation of trifluoroacetyl-substituted 4H-chromenes and 1H-benzo[f]chromenes with 6-amino-1,3-dimethyluracil and 6-aminothiouracil afforded a number of pyrido[2,3-d]pyrimidine derivatives containing a 2-hydroxybenzyl or 2-hydroxynaphthalen-1-ylmethyl group in the 6-position as a result of cascade transformation initiated by Michael addition. © 2017, Pleiades Publishing, Ltd

Reaction of Push-Pull Enaminoketones and in Situ Generated ortho-Quinone Methides: Synthesis of 3-Acyl-4H-chromenes and 2-Acyl-1H-benzo[f]chromenes as Precursors for Hydroxybenzylated Heterocycles

A simple and efficient method for the synthesis of 4H-chromenes and 1H-benzo[f]chromenes containing a trifluoroacetyl or aroyl group in the pyran ring from o-quinone methide precursors and push-pull enaminoketones has been developed. The chromenes are presumably formed through an initial oxa-Diels-Alder reaction, followed by an elimination of amine. The possibility of further transformations of given chromenes to o-hydroxybenzylated pyrazoles, isoxazoles, and pyridines has been demonstrated. © 2017 American Chemical Society

Reactions of 1-[(dimethylamino)methyl]naphthalen-2-ols with cyclic push-pull nitroenamines

[Figure not available: see fulltext.] A method was developed for the synthesis of 1-[2-nitro-2-(pyrrolidin-2-ylidene)ethyl]- and 1-[2-(imidazolidin-2-ylidene)-2-nitroethyl]-naphthalen-2-ols based on a reaction of 1,2-naphthoquinone-1-methide precursors with heterocyclic β-nitroenamines (pyrrolidine and imidazolidine derivatives). © 2018, Springer Science+Business Media, LLC, part of Springer Nature

Reactions of o-Quinone Methides with Halogenated 1H-Azoles: Access to Benzo[e]azolo[1,3]oxazines

A simple route to the series of azolo-condensed benzo[e][1,3]oxazines such as 9H-benzo[e][1,2,4]triazolo[5,1-b][1,3]oxazines, 9H-benzo[e]pyrazolo[5,1-b][1,3]oxazines, and 5H-benzo[e]imidazo[2,1-b][1,3]oxazines has been developed. The reaction proceeds through formation of an ortho-quinone methide intermediate followed by aza-Michael addition of the halogenoazoles to the o-quinone methide and intramolecular nucleophilic substitution. © Georg Thieme VerlagStuttgart · New York

Reactions of 1-[(dimethylamino)methyl]naphthalen-2-ols with cyclic push-pull nitroenamines

[Figure not available: see fulltext.] A method was developed for the synthesis of 1-[2-nitro-2-(pyrrolidin-2-ylidene)ethyl]- and 1-[2-(imidazolidin-2-ylidene)-2-nitroethyl]-naphthalen-2-ols based on a reaction of 1,2-naphthoquinone-1-methide precursors with heterocyclic β-nitroenamines (pyrrolidine and imidazolidine derivatives). © 2018, Springer Science+Business Media, LLC, part of Springer Nature

Reaction of trifluoroacetylchromenes with 6-aminouracils. Synthesis of pyrido[2,3-d]pyrimidines

The condensation of trifluoroacetyl-substituted 4H-chromenes and 1H-benzo[f]chromenes with 6-amino-1,3-dimethyluracil and 6-aminothiouracil afforded a number of pyrido[2,3-d]pyrimidine derivatives containing a 2-hydroxybenzyl or 2-hydroxynaphthalen-1-ylmethyl group in the 6-position as a result of cascade transformation initiated by Michael addition. © 2017, Pleiades Publishing, Ltd

Reactions of o-Quinone Methides with Halogenated 1H-Azoles: Access to Benzo[e]azolo[1,3]oxazines

A simple route to the series of azolo-condensed benzo[e][1,3]oxazines such as 9H-benzo[e][1,2,4]triazolo[5,1-b][1,3]oxazines, 9H-benzo[e]pyrazolo[5,1-b][1,3]oxazines, and 5H-benzo[e]imidazo[2,1-b][1,3]oxazines has been developed. The reaction proceeds through formation of an ortho-quinone methide intermediate followed by aza-Michael addition of the halogenoazoles to the o-quinone methide and intramolecular nucleophilic substitution. © Georg Thieme VerlagStuttgart · New York

Reaction of Push-Pull Enaminoketones and in Situ Generated ortho-Quinone Methides: Synthesis of 3-Acyl-4H-chromenes and 2-Acyl-1H-benzo[f]chromenes as Precursors for Hydroxybenzylated Heterocycles

A simple and efficient method for the synthesis of 4H-chromenes and 1H-benzo[f]chromenes containing a trifluoroacetyl or aroyl group in the pyran ring from o-quinone methide precursors and push-pull enaminoketones has been developed. The chromenes are presumably formed through an initial oxa-Diels-Alder reaction, followed by an elimination of amine. The possibility of further transformations of given chromenes to o-hydroxybenzylated pyrazoles, isoxazoles, and pyridines has been demonstrated. © 2017 American Chemical Society