61 research outputs found
Regioselective dehydrative intramolecular heteroannulation of beta-allyl-beta-hydroxy dithioesters: facile and straightforward entry to 2H-thiopyrans
No full textbeta-Allyl-beta-hydroxy dithioesters have been employed in the synthesis of hitherto unreported and synthetically demanding 2H-thiopyrans via regioselective intramolecular annulation strategy. Lewis acid BF3 center dot Et2O efficiently mediates the regioselective dehydration followed by intramolecular thioannulation at room temperature. The attractive features of this protocol include mild conditions, high atom-economy and excellent yields with the elimination of water as the only by-product. (C) 2013 Elsevier Ltd. All rights reserved
Selective photodissociation of highly photoactive Bis-2-benzylidenemalononitrile in solution
No full textPhotophysical study of highly photoactive bis(-2)-benzylidenemalononitrile (BBM) has been investigated in solution using UV-vis, fluorescence and NMR spectroscopic techniques. The seletive photodissociation can be attributed to the presence of highly polarized C=C bond, attached to dicyno groups (CN). Nevertheless, the observed photodissociation of BBM is highly solvent specific and temperature sensitive. The product A (2-(4-formylbenzylidene)malononitrile), formed by the selective photodissociation of BBM under UV irradiation has been isolated and identified by NMR studies. The photodissociation followed the pseudo 1st order kinetics with a rate constant (k) 10(-3).10(-4).s(-1). Moreover the mechanistic study of selective photodissociation of bis(-2)-benzylidenemalononitrile (BBM) has been investigated and found to follow the dipolar mechanism path during photochemical reaction
Dithioester-enabled chemodivergent synthesis of acids, amides and isothiazoles via C C bond cleavage and C O/C N/C S bond formations under metal- and catalyst-free conditions
No full textChemInform Abstract: Advances of Azide‐Alkyne Cycloaddition‐Click Chemistry over the Recent Decade
No full textChemInform Abstract: Progress in 1,3‐Dipolar Cycloadditions in the Recent Decade: An Update to Strategic Development Towards the Arsenal of Organic Synthesis
No full textProgress in 1,3-dipolar cycloadditions in the recent decade: an update to strategic development towards the arsenal of organic synthesis
No full textScheme 1. Atom economic synthesis of triazolobenzodiazepines. 1,3-Dipolar cycloaddition of primary amino esters, aldehydes, and activated alkenes is a well-established three-component reaction [16][17][18][19][20][21]. The azomethine ylides derived from deprotonation of iminium ions are CO2R-stabilized ylides A (Figure 2A) [22][23][24][25][26][27][28][29][30]. In recent years, our lab has reported a series of azomethine ylides A-based [3 + 2] cycloadditions for diverse heterocyclic scaffolds [31][32][33][34][35], including one-pot [3 + 2] and click reactions for triazolobenzodiazepines [32
In/I2 mediated functional group transformation: a direct approach toward the selective conversion of dithioester to ester
No full textA facile, direct approach for the selective conversion of dithioester to ester functional group has been developed. In/I2 in methanol efficiently promotes the interesting functional group transformation at room temperature. Applying the newly developed mild conditions, a series of α-allyl-β′-oxodithioesters have been converted to the corresponding α-allyl-β′-oxoesters in moderate to good yields. Interestingly, during the transformation the dithioester groups of the starting α-allyl-β′-oxodithioesters are selectively transformed to the corresponding methyl esters while the other functionalities within the moiety remained unaffected; hence requires no cumbersome protection–deprotection during the synthetic transformation
ChemInform Abstract: Metal‐Free Broensted Acid Mediated Synthesis of Fully Substituted Thiophenes via Chemo‐ and Regioselective Intramolecular Cyclization of α,α′‐Bis(β‐oxodithioesters) at Room Temperature.
No full textCatalyst-Free One-Pot Access to Pyrazoles and Disulfide-Tethered Pyrazoles via Deamidative Heteroannulation of beta-Ketodithioesters with Semicarbazide Hydrochloride in Water
No full textAn operationally simple, mild, and catalyst-free one-pot protocol to access privileged pyrazoles and disulfide-tethered pyrazoles has been devised by 3+2] heteroannulation of beta-ketodithioesters with semicarbazide hydrochloride in water under open air. The pH of the medium played a key role toward the selectivity switch, as refluxing in water led to the formation of pyrazoles, whereas addition of sodium acetate in water enabled the formation of disulfide-tethered pyrazoles. Notably, this protocol involves a tandem sequence of amination/cyclization/dehydration/hydrodesufurization/hydrolysis/deamida tive reactions. A mechanistic rationale for this regio-/chemoselective domino reaction is outlined, which is well supported and validated by density functional theory calculations
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