Domino Reactions of Chromones with Heterocyclic Enamines

Abstract

Domino reactions of heterocyclic enamines with chromone derivatives provides a convenient synthesis of a great variety of annulated heterocyclic ring systems. The course of the reaction depends on the type of substituent located at position 3 of the chromone. Reactions of 3-unsubstituted chromones, 3-nitrochromones, and 3-halochromones proceed by conjugate addition of the carbon atom of the enamine to carbon C-2 of the chromone, ring cleavage, and recyclization via the chromone carbonyl group. In the case of 3-formylchromes, 3-dichloroacetylchromone, 3-perfluoroalkanoylthiochromones, 3-(2-fluorobenzoyl)chromones, and 3-methoxalylchromones the final cyclization proceeds via the carbonyl group located outside the chromone moiety. The functional groups located at the carbonyl group at position 3 of the chromone allow for further synthetic transformations including additional ring closures.Contents1 Introduction2 3-Unsubstituted Chromones3 3-Nitrochromones4 3-Formylchromes5 3-Dichloroacetylchromone6 3-Perfluoroalkanoylthiochromones7 3-Methoxalylchromones8 3-(2-Fluorobenzoyl)chromones9 3-Halochromones10 Chromone-3-carboxylic Acids11 Conclusions

The Many Chemists Who Could Have Proposed the Woodward‐Hoffmann Rules But Didn't: The Organic Chemists Who Discovered the Smoking Guns[]**

“…"Domino" has been used often in terms of reaction sequences. [168,169] Doering was likely implying that when the methyl group at the lower right corner of the trans-3,4-dimethylcyclobutene in Figure 19 rotates upward (counterclockwise), the other methyl group rotates downward in a consequentially-coupled fashion, a domino effect, one motion requiring another. If that was Doering's intent, then that hypothesis was a distraction from orbital symmetry control, where the direction of motion of the αand ω-terminal groups would rotate conrotatory or disrotatory depending on whether the number of electrons in the electrocyclization were 4n or 4n + 2, respectively, for thermal reactions and the opposite coupled direction for photochemical reactions.…”

“…A “domino effect” generally refers to a situation in which one event sets off a chain of similar events. “Domino” has been used often in terms of reaction sequences [168,169] . Doering was likely implying that when the methyl group at the lower right corner of the trans ‐3,4‐dimethylcyclobutene in Figure 19 rotates upward (counterclockwise), the other methyl group rotates downward in a consequentially‐coupled fashion, a domino effect, one motion requiring another.…”

Synthesis of Purines and Related Molecules by Cyclization ­Reactions of Heterocyclic Enamines

“…The idea was to prepare novel fluorinated and non-fluorinated purine isosteres by cyclizations of heterocyclic enamines, soft 1,3dinucleophiles, with 1,3-dielectrophiles earlier used in our research group. 17 The present article aims to give a personalized account on our work on such cyclization reactions of heterocyclic enamines with various electrophiles.…”

Adventures in CH-Arylation Chemistry

“…In 2010, based on my experience with cyclization reactions of 1,3-bis(silyl enol ethers) with chromones, 4l we started a new project related to ring-transformation reactions of chromones with heterocyclic enamines. 11 In addition, we started to investigate the synthesis of fluorinated, nitro-and amino-substituted purine analogues by cyclization of heterocyclic enamines with various 1,3-dielectrophiles. 12 In this context and based on our experience in the field of Pd-catalyzed cross-coupling reactions, we became more and more interested in CH activation reactions of heterocyclic substrates and their applications.…”