The fusion of fluorine in drug molecules through different fluorinating reagents remains a cornerstone in pharmaceutical chemistry. Progress in the field of deoxyfluorination through the development of novel reagents has...
The diverse biological activities of nitrogen-containing compounds make the construction of the C–N bond of great importance. As N-fluorobenzenesulfonimide, one of the most abundant chemical feedstocks, having dual behaviour i.e....
Transition-metal-free regioselective synthesis of functionalized amino-indenonesb yt he reaction of orthoalkynylaldehydes with ab road range of primarya mines by intramolecular cyclization has been described. The designed reactionp roceedst hrough KOH-mediated Prinstype cyclization and DMSO-promoted oxidation of the cyclopent-2-en-1-one system. The proposed mechanism and role of solvent were well supported by control experiments. For the first time, we have disclosed the reverser eactivity of (2-alkynyl)-arylaldimines in as uper basic system. The synthesis of highly substituted indenones during the past decades has received significant attention. [1] These heterocycles are acrucial structural motif of euplectin, [2] and are also essentials tarting materials for the p-stacked polybenzofulvene hosts. [3] The indenone framework also found in many natural products and bioactive molecules ( Figure 1). [4] Methods for the synthesis of substituted indenones include the traditional Friedel-Crafts cyclizations, [5][6] photochemical reactions, [7] Nazarov cyclization, [8] and Aldol condensation. [9] Transition-metal-catalyzed [10][11][12][13] approaches have also been reported,i ncluding direct CÀHa nnulations, [14] Heck-Larock annulations, [15] alkyne annulation reactions, [16] and Rh-catalyzed CÀHa ctivation. [17] Indenones have also been synthesized by metal-free approaches through radical [18] or ionic pathways, [19] and also by MeOTf-induced carboannulated cyclization. [20] Nevertheless, such methodsm ake use of availablea lkynes as starting materials and transition-metal-based catalysts and are less relevant to the synthesis of indenones bearing arylamino or long/short alkylamino side chains. Therefore, the development of transition-metal-free approaches for the synthesis of highly functionalized amino-indenonesi so fi mmense importance.In the last decades, many groups reported the exo and endo-digc yclization of (2-alkynyl)-arylaldimines [21] using iodine, [22a] aL ewis acid, [22b] and transition-metal catalyst. [23] These reports involved the activation of the alkyne followed by nucleophilic attack onto the alkyne.H owever,o ur methodology describes the use of KOH/DMSO to promote the regioselective direct synthesis of functionlized amino-indenones by using a wide range of ortho-alkynylaldehydesa nd primary amines to generate (2-alkynyl)-arylaldimines species, whichc ould give rise to aP rins-type [24] ring closure onto the carbonyl carbon centerf ollowed by DMSO-promoted oxidation (Figure 2).Various research groups have made significant progressi n the transition-metal-free synthesis of heterocycles and carbocycles. [25] Our group has also been involved in the metal-free synthesis of biologically active heterocyclic and carbocyclic cores. [26] Along with our ongoing metal-free research in tandems ynthesis, herein, we report at ransition-metal-free tandema pproachf or the synthesis of amino-1H-indenone by the reactiono fortho-alkynylaldehydes with ab road range of primary amines. Figure 1. Biologically act...
A regioselective tandem approach for annulated napthyridines/isoquinolines embedded with the phosphine oxide group under mild reaction conditions has been achieved in good to excellent yields. The designed strategy involves the triflateinduced formation of new C sp 3 −P and C sp 2 −N bond formation in one pot. This protocol was also well tolerated for the construction of densely functionalized organo-phosphorylated chromenes in good yields. Further, phosphino-derived sulfamethazine and sulfamethoxazole drugs were also successfully synthesized in good yields. The mechanistic studies revealed that the ionic pathway and the formation of regioselective 6-endo dig cyclized products were confirmed through X-ray crystallographic studies. Interestingly, photophysical studies of selectivity selected compounds revealed their stimulating fluorescence properties.
A metal‐free, versatile triple‐bond directed approach for the decarbonylative C−H amination of ortho‐alkynyl quinoline/pyridine aldehydes using N‐fluorobenzenesulfonimide as nitrogen source under mild reaction conditions has been described. The designed reaction strategy was triggered by trapping of fluorine by base with subsequent attack of bis(phenylsulfonyl)‐λ2‐azane on the carbonyl carbon of a heterocycle, which was gradually converted into the corresponding amine through a Curtius type rearrangement. This protocol provides a one‐step approach for the conversion of aldehydes into amines in good yields. The synthesized amines were successfully transformed into biologically important pyrroloquinolines/pyridines.
A radical promoted approach for the selective synthesis of furo[3,2‐b]quinolines and benzylidene‐1,3‐dihydrofuro[3,4‐b]quinolines have been achieved from 2‐alkynyl quinoline‐3‐carbaldehydes by fine‐tuning of base and oxidant in good yields. In the presence of an oxidant, the reaction afforded the 5‐endo‐dig cyclized furoquinolines by decarbonylative intramolecular cyclization via a Dakin‐type reaction; however, in the absence of oxidant, 5‐exo‐dig cyclized products were obtained selectively through reductive intramolecular cyclization. The formation of furoquinolines was further supported by X‐ray crystallographic studies. The proposed mechanism was well supported by the control experiments.
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