Manab Chakravarty

Cycloaddition Reactions of Allenylphosphonates and Related Allenes with Dialkyl Acetylenedicarboxylates, 1,3-Diphenylisobenzofuran, and Anthracene

Cycloaddition reactions of allenylphosphonates [(RO)(2)P(O)[(R(1))C═C═CR(2)(2)] with dialkyl acetylenedicarboxylates, 1,3-diphenylisobenzofuran, and anthracene have been investigated and compared with those of allenoates [(EtO(2)C)RC═C═CH(2)] and allenylphosphine oxides [Ph(2)P(O)(R(1))C═C═CR(2)(2)] in selected cases. Allenylphosphonates (RO)(2)P(O)(Ar)C═C═CH(2) with an α-aryl group preferentially undergo [4 + 2] cycloaddition with DMAD/DEAD under thermal activation, but in addition to the expected 1:1 (allene: DMAD) product, the reaction also leads to 1:2 as well as 2:1 products that were not reported before. When an extra vinyl group is present at the γ-carbon of allenylphosphonate [e.g., (OCH(2)CMe(2)CH(2)O)P(O)(Ph)C═C═CH(C═CHMe)], [4 + 2] cycloaddition takes place utilizing either the vinylic or the aryl end, but additionally a novel cyclization wherein complete opening of the [β,γ] carbon-carbon double bond of the allene is realized. In contrast to these, the reaction of allenylphosphonate (OCH(2)CMe(2)CH(2)O)P(O)(H)C═C═CMe(2) possessing a terminal ═CMe(2) group with DMAD occurs by both [2 + 2] cycloaddition and ene reaction. While the reaction of ═CH(2) terminal allenylphosphonates as well as allenylphosphine oxides with 1,3-diphenylisobenzofuran afforded preferentially endo-[4 + 2] cycloaddition products via [α,β] attack, the analogous allenoates [(EtO(2)C)RC═C═CH(2)] underwent exo-[4 + 2] cyclization. Under similar conditions, allenylphosphonates with a terminal ═CR(2) group gave only [β,γ]-cycloaddition products. An unusual ring-opening of a [4 + 2] cycloaddition product followed by ring-closing via [4 + 4] cycloaddition, as revealed by (31)P NMR spectroscopy, is reported. Anthracene reacted in a manner similar to 1,3-diphenylisobenzofuran, albeit with lower reactivity. Key products, including a set of exo- and endo- [4 + 2] cycloaddition products, have been characterized by single crystal X-ray crystallography.

Benzylic Phosphates in Friedel–Crafts Reactions with Activated and Unactivated Arenes: Access to Polyarylated Alkanes

Easily reachable electron-poor/rich primary and secondary benzylic phosphates are suitably used as substrates for Friedel-Crafts benzylation reactions with only 1.2 equiv activated/deactivated arenes (no additional solvent) to access structurally and electronically diverse polyarylated alkanes with excellent yields and selectivities at room temperature. Specifically, diversely substituted di/triarylmethanes are generated within 2-30 min using this approach. A wide number of electron-poor polyarylated alkanes are easily accomplished through this route by just tuning the phosphates.

Structure and reactivity of tautomeric forms of zwitterionic species from the reaction of phosphorus(III) compounds with electron deficient alkenes and alkynes

Synthesis and reactivity of tautomeric forms of the zwitterions proposed in the phosphine catalysed transformations of electron-deficient alkenes/alkynes using the heterocycles [(t-BuNH)PN-t-Bu]2 (1) and Ph2P(NH-t-Bu) (2) are discussed. Thus, compounds (t-BuNH)P(N-t-Bu)2P(N-t-Bu)CHCH(CO2Me) (3), (t-BuNH)P(N-t-Bu)2P(N-t-Bu)CH2CH2(CN) (4) and Ph2P(N-t-Bu){C(Ph)CH(CO2Et)} (5) are isolated. A novel heterocycle [(t-BuNH)P(N-t-Bu)2P[C(CO2Me)–CH(OMe)–C(O)–N(t-Bu)–] (6) obtained by utilizing 1 and MeO2CCCCO2Me is described. The structural proof for the second stage intermediate after the addition of phenols/carboxylic acids to the zwitterions formed in the reaction of electron deficient alkenes with PIII compounds [e.g. {(t-BuNH)P(N-t-Bu)2P(NH-t-Bu)CH2CH2(CN)}+{X}− where X = PhO− + PhOH (7·Ph–O–H⋯OPh), 4-NO2–C6H4–CO2− + H2O (8·H2O)] is also provided for the first time. X-Ray structural characterisation of 3–8 has also been accomplished.

Triflic acid mediated functionalization of α-hydroxyphosphonates: route for sulfonamide phosphonates

An operationally simple synthetic method for (±)-α-aryl/methylsulfonamidomethylphosphonates and new (±)-γ-aryl/methyl sulfonamidomethylvinylphosphonates has been developed through straightforward reactions of (±)-α-hydroxyphosphonates with sulfonamides in the presence of triflic acid (TfOH) at room temperature in a vessel open to air. For γ-dimethylallylhydroxyphosphonate, the (E)-1,3-butadienylphosphonate was formed quantitatively using TfOH while FeCl3 afforded the expected product in moderate yield unpredictably. The favourable sulfonoamidation of benzyl alcohol is also observed when TfOH was used for α-hydroxyphosphonates having a benzyloxy group.

Easy access to new anthracenyl π-conjugates: generation of distinct AIE-active materials

Inspired by the well-established distyryl anthracenyl (DSA) π-conjugates as aggregation-induced emission active (AIE) materials and the evolution of the synthesis/optoelectronic properties of numerous anthracene-based π-conjugates, a new series of 9-or 10-(hetero)arylated anthracenyl π-conjugates were synthesized using a straightforward and metal-free protocol by starting with a unique family of organophosphonates. The fluorescence behaviors of these (hetero)arylated π-conjugates were systematically studied to determine their AIE-activities, resulting in a new class of much smaller anthracene-based AIEgens. Considerable effort was made to analyze the AIE-behaviors of selected molecules by performing single crystal X-ray diffraction, time-resolved fluorescence, and dynamic light scattering studies. Our mechanistic investigations reveal that the heteroarene(s) linked to a π-conjugated system facilitate the AIE-behaviors of these molecules. Fluorescence microscopy images of the selected compounds in both molecular and aggregated form were obtained to demonstrate their structure–property relationship. Further, a trisubstituted anthracene-based π-conjugate was synthesized and established as a new AIEgen.

Haloarene-Linked Unsymmetrically Substituted Triarylethenes: Small AIEgens To Detect Nitroaromatics and Volatile Organic Compounds

Unsymmetrically substituted triarylalkenes as aggregation-induced emission-active fluorogens (AIEgens) are sporadically explored by different researchers. In this Article, naphthalene, biphenyl, and haloarene-linked new triarylethenes are conveniently synthesized and presented as unsymmetrically substituted extensive π-conjugates to continue the discovery of small molecules as new AIEgens. Moreover, fluorophores attached to haloarenes are noteworthy, but such compounds are barely investigated as AIEgens. The possible mechanism underlying this AIE-behavior has also been addressed by the support of experimental/theoretical outcomes. Moreover, two of these small AIEgens are fruitfully employed for rapid sensing of nitroaromatic compounds (NACs) where picric acid (PA, as a model explosive) showed a strong quenching efficiency with the detection limit of 39 or 48 ppb along with other nitroaromatics such as p-nitrotoluene and p-nitrophenol. This quenching could be visualized by the naked eye under a UV (365 nm) lamp and performed almost in an aqueous medium. Such alkenes are also proved to exhibit very clean on/off fluorescence switching properties for polar volatile organic compounds (VOCs).

Radiolytic Degradation in Lanthanide/Actinide Separation Ligands–NOPOPO: Radical Kinetics and Efficiencies Determinations

Abstract Trivalent lanthanide/actinide separations from used nuclear fuel occurs in the presence radiation fields that degrades the extraction ligands and solvents. Here we have investigated the stability of a new ligand for lanthanide/actinide separation; 2,6-bis[(di(2-ethylhexyl)phosphino)methyl] pyridine N,P,P-trioxide, TEH(NOPOPO). The impact of γ-radiolysis on the distribution ratios for actinide (Am) and Lanthanide (Eu) extraction both in the presence and absence of an acidic aqueous phase by TEH(NOPOPO) was determined. Corresponding reaction rate constants for the two major radicals, hydroxyl and nitrate, were determined for TEH(NOPOPO) in the aqueous phase, with room temperature values of (3.49 ± 0.10) × 109 and (1.95 ± 0.15) × 108 M–1 s–1, respectively. The activation energy for this reaction was found to be 30.2 ± 4.1 kJ mol–1. Rate constants for two analogues (2-methylphosphonic acid pyridine N,P-dioxide and 2,6-bis(methylphosphonic acid) pyridine N,P,P-trioxide) were also determined to assist in determining the major reaction pathways.

Non-stoichiometry induced by differential oxygen/lone pair occupation in chiral bicyclic 1,1′-binaphthoxy cyclodiphosphazanes

Non-stoichiometry and isostructurality in a set of chiral phosphorus compounds as a result of lone pair/oxygen exchange, substantiated by the combined use of 31P NMR spectroscopy and X-ray crystallography, is described.

Reaction of allenylphosphonates/allenylphosphine oxides with thiocyanates/isothiocyanates or oxalyl chloride/AgNO3

GRAPHICAL ABSTRACT ABSTRACT In this paper, we describe thiocyanation as well as chlorination of selected allenylphosphonates/allenyl phosphine oxide, using ammonium thiocaynate or (OCH2CMe2CH2O)PNCS (for thiocyanation) or oxalyl chloride/AgNO3 for chlorination. The resulting products are vinyl (thiocyanato)phosphonates or vicinal dichloro(vinyl) phosphonates. One of the vinyl thiocyanato-phosphonates is characterized by single crystal X-ray crystallography.