Author
K. Praveen Kumar
Other affiliations: Indian Institute of Chemical Technology
Bio: K. Praveen Kumar is an academic researcher from University of Hyderabad. The author has contributed to research in topics: Phosphonate & Sodium hydride. The author has an hindex of 9, co-authored 26 publications receiving 240 citations. Previous affiliations of K. Praveen Kumar include Indian Institute of Chemical Technology.
Topics: Phosphonate, Sodium hydride, Phosphorane, Michael reaction, Catalysis
Papers
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TL;DR: Iodine is found to be a highly efficient catalyst for the three-component coupling (3CC) of aldehydes, β-naphthol, and 1,3-dimethylbarbituric acid under solvent-free conditions to afford the corresponding 8,10-dimyl-12-aryl-12 H -naphTHo[1′,2′5,6]pyrano[2,3]-d ]pyrimidine-9,11-diones in good yields with high selectivity as discussed by the authors.
37 citations
TL;DR: New chlorophosphonates bearing a 1,3,2-dioxaphosphorinane ring which are useful for the stereospecific synthesis of 5-chlorofurfuryl substituted olefins and chloro-substituted dienes have been obtained by an easy, inexpensive route.
Abstract: New chlorophosphonates bearing a 1,3,2-dioxaphosphorinane ring which are useful for the stereospecific synthesis of 5-chlorofurfuryl substituted olefins and chloro-substituted dienes have been obtained by an easy, inexpensive route. The utility of some of these in the synthesis of ferrocenyl- and anthracenyl-substituted unsymmetrical acetylenes has been explored. The structures of the phosphonates (OCH2CMe2CH2O)P(O)CH2(C4H2ClO) (4) and (OCH2CMe2CH2O)P(O)(CHCHCH(Cl)Ph (7) have been determined; in addition, the stereochemistry of (5-chlorofurfuryl)CHCH(4-ClC6H4) (13b) and 2,4-Cl2C6H3−CHCH−CHC(Ph)Cl (14a) is unambiguously proved by the X-ray structure determination.
36 citations
TL;DR: Structural characterization of compounds analogous to the proposed intermediates in the Mitsunobu esterification process is achieved by the combined use of NMR spectroscopy and X-ray diffractometric studies.
Abstract: Structural characterization of compounds analogous to the proposed intermediates in the Mitsunobu esterification process is achieved by the combined use of NMR spectroscopy and X-ray diffractometric studies. The results show that compounds (t-BuNH)P(μ-N-t-Bu)2P[(N-t-Bu)(N-(CO2R)-N(H)(CO2R))] [R = Et (11), i-Pr (12)], obtained by treating [(t-Bu-NH)P-μ-N-t-Bu]2 (10) with diethylazodicarboxylate (DEAD) or diisopropylazodicarboxylate (DIAD), respectively, have a structure with the NH proton residing between the two nitrogen atoms ((P)N(t-Bu) and (P)N-N(CO2Et)); this is the tautomeric form of the expected betaine (t-BuNH)P(μ-N-t-Bu)2P+[(NH-t-Bu)(N-(CO2R)-N-(CO2R)]. Treatment of ClP(μ-N-t-Bu)2P[(N-t-Bu){N-(CO2-i-Pr)-N(H)(CO2-i-Pr)] (6) with 2,6-dicholorophenol affords (2,6-Cl2-C6H3-O)P(μ-N-t-Bu)2P+[(NH-t-Bu){N[(CO2i-Pr)(HNCO2i-Pr)]}](Cl-)(2,6-Cl2-C6H3-OH) (14) that has a structure similar to that of (CF3CH2O)P(μ-N-t-Bu)2P+[(NH-t-Bu){N[(CO2i-Pr)(HNCO2i-Pr)]}](Cl-) (13), but with an additional hydrogen bonded ph...
25 citations
TL;DR: In this paper, the structural preference of spirocyclic penta- and tricyclic hexacoordinate (amino)oxyphosphoranes has been examined in an effort to delineate the structural preferences in spirocycleic pentanaphoric compounds.
Abstract: The reaction of diethyl azodicarboxylate (DEAD) or diisopropyl azodicarboxylate (DIAD) with cyclic phosphites/phosphoramidites has been examined in an effort to delineate the structural preferences in spirocyclic penta- and tricyclic hexacoordinate (amino)oxyphosphoranes. It is shown that the familiar Bent’s or apicophilicity rules referred to in standard books give an oversimplified picture. Thus the reaction of CH2(6-t-Bu-4-Me–C6H2O)2PCl (19) with DEAD/DIAD leads to the chlorophosphoranes CH2(6-t-Bu-4-Me–C6H2O)2PCl[N(COOR)–NC(OR)O–] [R = Et (21a), i-Pr (21b)]. Treatment of 21a–b with pyrazole or imidazole leads to CH2(6-t-Bu-4-Me–C6H2O)2P(NRR′)[N(COOR)–NC(OR)O–] [NRR′ = pyrazolyl (12a–b), imidazolyl (13a–b)] that have trigonal bipyramidal phosphorus with ‘reversed apicophilicity’. Compound S(6-t-Bu-4-Me–C6H2O)2P(NH–i-Pr) (20b) affords the pentacoordinate derivative S(6-t-Bu-4-Me–C6H2O)2P(NH–i-Pr)[N(COOR)–NC(OR)O–] (15), but S(6-t-Bu-4-Me–C6H2O)2PCl (20a) gives the hexacoordinate phosphorane S(6-t-Bu-4-Me–C6H2O)2PCl[N(COOR)–NC(OR)O–] (16) with the shortest known S→P coordinate bond. Compound 15 also exhibits the ‘reversed apicophilicity’ phenomenon, but the disposition of substituents is different from that in 12–13. The compound S(6-t-Bu-4-Me–C6H2O)2PPh[N(COOR)–NC(OR)O–] (17) is prepared similarly. Reaction of 16 with imidazole gives S(6-t-Bu-4-Me–C6H2O)2P(imidazolyl)[N(COOR)–NC(OR)O–] (18). Both 17 and 18 show distorted octahedral geometry with S→P coordination, but the sulfur is trans to the phenyl/imidazolyl group (while it is cis to –Cl in 16). The variable temperature 31P NMR spectra of 15 exhibit four totally distinct signals showing a dynamic behaviour with isomeric pentacoordinate species present. Theoretical calculations suggest that the compound as isolated is the favoured one for S(6-t-Bu-4-Me–C6H2O)2P{(N-t-Bu)[N(CO2Et)NH(CO2Et)]} (2, previously reported) as well as 15 and 16.
23 citations
TL;DR: The α-chlorophosphonates (OCH2CMe2CH2O)P(O)CHCl-C6H4-4-R [R=H (4), Me (5), OMe (6)], which are now readily accessible, react with ketones in the presence of NaH (without recourse to the more expensive t-BuLi) to afford trisubstituted vinyl halides as discussed by the authors.
21 citations
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TL;DR: This review concludes that Etherification without Cyclization and N-Alkylation should be considered as separate science, and the proposed treatment of Etherification with Cyclization as a separate science should be reconsidered.
Abstract: 10. Patented Literature 2616 10.1. Esterification 2616 10.2. Ether Formation 2619 10.2.1. Etherification without Cyclization 2619 10.2.2. Etherification with Cyclization 2624 10.3. N-Alkylation 2625 10.4. Other Reactions 2627 11. Summary and Outlook 2628 12. Note Added in Proof 2628 13. Abbreviations Used in This Review 2629 14. Acknowledgments 2629 15. Supporting Information Available 2630 16. References 2630
909 citations
TL;DR: The synergistic effect of the combined use of MCRs and molecular iodine for the development of new eco-compatible methodologies for organic chemistry is highlighted.
Abstract: The multicomponent reactions (MCRs) consist of two or more synthetic steps which are carried out without isolation of any intermediate thus reducing time, saving money, energy and raw materials. The development of MCRs in the presence of molecular iodine is an efficient approach that meets with the requirements of sustainable chemistry. The aim of this review is to highlight the synergistic effect of the combined use of MCRs and molecular iodine for the development of new eco-compatible methodologies for organic chemistry.
158 citations
TL;DR: This review investigates the use of complex ester fragment couplings within natural product total synthesis campaigns and presents and discusses a collection of successful examples from the literature.
133 citations
TL;DR: The structures of key compounds are established by X-ray crystallography and utility of the phosphonate products in the Horner-Wadsworth-Emmons reaction is demonstrated.
Abstract: Coupling reactions of allenylphosphonates (OCH2CMe2CH2O)P(O)CHCCRR‘ [R, R‘ = H (1a), R = H, R‘ = Me (1b), R = R‘ = Me (1c)] with aryl iodides, iodophenol, and iodobenzoic acid in the presence of palladium(II) acetate are investigated and compared with those of phenylallenes PhCHCCR2 [R = H (2a), Me (2b)] and allenyl esters EtO2CCHCCR2 [R = H (2c), Me (2d)]. While 1b and 1c couple with different stereochemical outcomes using PhI in the presence of Pd(OAc)2/PPh3/K2CO3 to give phenyl-substituted 1,3-butadienes, 1a does not undergo coupling but isomerizes to the acetylene (OCH2CMe2CH2O)P(O)C⋮CMe (7). In the reaction of 1c with PhI, use of K2CO3 affords the butadiene (Z)-(OCH2CMe2CH2O)P(O)CHC(Ph)−C(Me)CH2 (12); in contrast, the use of Ag2CO3 leads to the allene (OCH2CMe2CH2O)P(O)C(Ph)CCMe2 (20), showing that these bases differ very significantly in their roles. The reaction of 1a with PhI or PhB(OH)2 in the presence of Pd(OAc)2/CsF/DMF leads mainly to (E)-(OCH2CMe2CH2O)P(O)CHC(Me)Ph (21) and (OCH2CMe2CH2O)P(O)...
96 citations
TL;DR: In this article, the synthesis and properties of these special classes of ferrocenes having olefinic, and acetylenic and cumulenic backbones are discussed and a review of their properties is presented.
86 citations