Coupling reactions of allenylphosphonates (OCH(2)CMe(2)CH(2)O)P(O)CH=C=CRR' [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 PhCH=C=CR2 [R = H (2a), Me (2b)] and allenyl esters EtO(2)CCH=C=CR(2) [R = H (2c), Me (2d)]. While 1b and 1c couple with different stereochemical outcomes using PhI in the presence of Pd(OAc)(2)/PPh(3)/K(2)CO(3) to give phenyl-substituted 1,3-butadienes, 1a does not undergo coupling but isomerizes to the acetylene (OCH(2)CMe(2)CH(2)O)P(O)CCMe (7). In the reaction of 1c with PhI, use of K(2)CO(3) affords the butadiene (Z)-(OCH(2)CMe(2)CH(2)O)P(O)CH=C(Ph)-C(Me)=CH(2) (12); in contrast, the use of Ag(2)CO(3) leads to the allene (OCH(2)CMe(2)CH(2)O)P(O)C(Ph)=C=CMe(2) (20), showing that these bases differ very significantly in their roles. The reaction of 1a with PhI or PhB(OH)2 in (t)he presence of Pd(OAc)2/CsF/DMF leads mainly to (E)-(OCH(2)CMe(2)CH(2)O)P(O)CH=C(Me)Ph (21) and (OCH(2)CMe(2)CH(2)O)P(O)CH2-C(Ph)=CH(2) (22) and is thus a net 1,2-addition of Ph-H. Compound 1b reacts with iodophenol in the presence of Pd(OAc)(2)/PPh(3)/K(2)CO(3) to give a benzofuran that has a structure different from that obtained by using 1c under similar conditions. Treatment of 1a with iodophenol/Pd(OAc)(2)/CsF/DMF also gives a benzofuran whose structure is different from that obtained by using 2a under similar conditions. In the reaction with 2-iodobenzoic acid, 1a and 2c afford one type of isocoumarin, while 1b,c and 2a,b give a second type of isocoumarin. The structures of key compounds are established by X-ray crystallography. Utility of the phosphonate products in the Horner-Wadsworth-Emmons reaction is demonstrated.

No abstract

Steady development on photophysical behaviors for a variety of organic fluorophores inspired us to generate anthracene-based fluorescent molecules with a strong acceptor and a significantly weak donor through a π-spacer. Such molecules are found to have substantial twisted conformational orientations in the solid state and enhanced apolar character because of the attachment of tolyl or mesityl group with an anthracenyl core. Upon exposure to a variety of solvents, strong solvatochromism was noticed for 4-nitro compound (84 nm red shift) in contrast to the cyano analogue (18 nm red shift). Both these probes were highly emissive in apolar solvents while nitro-analogue, in particular, could discriminate the solvents of E T (30) (a measure of microscopic solvent polarity) ranging from 31 to 37. Thus, 4-nitro compounds can be successfully employed to detect and differentiate the apolar solvents. On the contrary, the 2-nitro analogue is almost nonemissive for the same range of solvents perhaps because of favorable excited-state intramolecular proton-transfer process. The fundamental understanding of solvatochromic properties through the formation of twisted intramolecular charge-transfer (TICT) state is experimentally analyzed by synthesizing and studying the π-conjugates linked to only benzene in place of nitro or cyanobenzene, which exhibits no solvatochromism and that helped finding the possible emission, originated from the locally excited state. Moreover, the molecular structures for these compounds are determined by the single-crystal X-ray diffraction studies to examine the change in emission properties with molecular packing and alignment in the aggregated state. The measurement of dihedral angles between the substituents and anthracenyl core was helpful in finding the possible extent of electronic conjugations within the system to decipher both solvatochromism and aggregation enhanced emission (AEE)-behavior. The cyano analogue exhibited prominent AEE-behavior, whereas nitro analogues showed the aggregation-caused quenching effect. The reason behind such dissimilarity in solvatochromism and AEE-behavior between cyano- and nitro-linked anthracenyl π-conjugates are also addressed through experimental outcomes.

A simple trimethoxybenzene-linked anthracenyl π-conjugate is developed for the ultra-sensitive and selective detection of TNT in solid, liquid and vapor phases. The TNT could also be detected in the field soil.

An FeCl3‐mediated regio‐ and stereoselective Friedel–Crafts‐type arylation of α‐hydroxy phosphonates with unactivated arenes has been developed in which the unstable allylphosphonate cations generated are stabilized by extended conjugation. The approach provides a simple, efficient and economic approach to highly demanding stereoselective γ‐aryl‐substituted vinylphosphonates and dialkyl (diarylmethyl)phosphonates with good regioselectivity. These reactions proceed under mild conditions and proceed in the absence of any additional solvent.

Molecularly nonstoichiometric crystals obtained as a result of differential occupation of sites with oxygen atom/phosphorus lone pair of electrons or with sulfur/selenium in three sets of phosphorus compounds are described. These are formed by a combination of (a) [CH2(6-t-Bu-4-MeC6H2O)2]PNMe2 (11) and [CH2(6-t-Bu-4-MeC6H2O)2]P(O)NMe2 (13), (b) [CH2(6-t-Bu-4-MeC6H2O)2]P(S)NMe2 (14) and [CH2(6-t-Bu-4-MeC6H2O)2]P(Se)NMe2 (15), and (c) [(2,6-Me2C6H3O)(O)P-micro-N-t-Bu]2 (16) and (2,6-Me2C6H3O)(O)P(micro-N-t-Bu)2P(O-2,6-Me2C6H3) (17). In the case of c, three different types of crystals with varying stoichiometry of 16 and 17 (1:9, 1:1.5, and 1:0.43) are obtained. The results are substantiated by the combined use of 31P NMR spectroscopy and X-ray crystallography. These observations suggest that we should be cautious with regards to the purity of samples when syntheses involving the oxidation of P(III) systems are reported. It is also emphasized that the apparent P-X distances in some of these crystals cannot actually be taken as true bond lengths.

No abstract

Reaction of the cyclodiphosphazane [(OC4H8N)P(μ‐N‐t‐Bu)2P(HN‐t‐Bu)] (1) with an equimolar quantity of diisopropyl azodicarboxylate afforded the phosphinimine product [(OC4H8N)P(μ‐N‐t‐Bu)2P=N‐t‐Bu)(N(CO2 ‐i‐Pr)NHCO2‐i‐Pr] (6) having a PIII‐N‐PV skeleton. Similar products [(t‐BuNH)P(μ‐N‐t‐Bu)2P=N‐t‐Bu)(N(CO2Et)NHCO2Et] (7) and [(CO2‐i‐Pr)HNN(CO2‐i‐Pr)](t‐BuN=P(μ‐N‐t‐Bu)2POCH2CMe2CH2O[P(μ‐N‐t‐Bu)2P=N‐t‐Bu)(N(CO2‐i‐Pr)NH(CO2‐i‐Pr)] (8) were spectroscopically characterized in the reaction of [(t‐BuNH)P‐N‐t‐Bu]2 (2) and [(t‐BuNH)P(μ‐N‐t‐Bu)2POCH2CMe2CH2OP(μ‐N‐t‐Bu)2P(NH‐t‐Bu)] (3) with diethyl‐ and diisopropyl azodicarboxylate, respectively. By contrast, the reaction of [(μ‐t‐BuN)P]2[O‐6‐t‐Bu‐4‐Me‐C6H2]2CH2 (4) and [(C5H10N)P‐μ‐N‐t‐Bu]2 (5) with diisopropyl azodicarboxylate afforded the mono‐ and bis‐oxidized compounds [(O)P(μ‐N‐t‐Bu)2P][O‐6‐t‐Bu‐4‐Me‐C6H2]2CH2 (9) and [(C5H10N)(O)P‐μ‐N‐t‐Bu]2 (10), respectively. Oxidative addition of o‐chloranil to 7 and its DIAD analogue [(t‐BuNH)P(μ‐N‐t‐Bu)2P=N‐t‐Bu)(N(CO2‐i‐Pr)NHCO2‐i‐Pr] (11) afforded [(C6Cl4‐1, 2‐O2)(t‐BuNH)P(μ‐N‐t‐Bu)2P=N‐t‐Bu)(N(CO2R)NHCO2R] [R = Et (12) and i‐Pr (13)] containing tetra‐ and pentacoordinate PV atoms in the cyclodiphosphazane ring. The structures of 6, 9, 12 and 13 have been confirmed by X‐ray structure determination. For comparison, the X‐ray structure of the double cycloaddition product [(C6Cl4‐1, 2‐O2)(t‐BuNH)PN‐t‐Bu]2 (14), obtained from the reaction of 2 with two mole equivalents of o‐chloranil is also reported.