Kaipenchery A. Kumar

Synthesis and alkali metal picrate extraction capabilities of novel cage-functionalized 17-crown-5 and 17-crown-6 ethers

The syntheses of three novel cage-functionalized 17-crown-5 and 17-crown-6 ethers, i.e., 10–12, are reported and the results of alkali metal picrate extraction experiments performed by using each of these crown ethers in turn as the extractant are described. Their respective relative extraction efficiencies toward alkali metal picrates were compared with the corresponding efficiencies of 15-crown-5 and benzo-15-crown-5 solutions at the same concentration. The extraction profile of 10 (17-crown-5) toward alkali metal picrates is similar to that of 15-crown-5; however, 10 displays 33% greater avidity toward Na+ picrate. The ability of 11 (benzo-17-crown-5) to extract Li+, Rb+, and Cs+ picrates is similar to that of benzo-15-crown-5. Crown ether 10 is ca. 3 times more effective than 11 toward extraction of K+ picrate. The alkali metal picrate extraction profile of 12 (17-crown-6) resembles that of 10; however, 12 shows enhanced avidity vis-a-vis 10 toward Na+, K+, Rb+, and Cs+ picrates.

Syntheses of bis- and tetra-crowned clefts and studies of their selectivities in metal ion complexation

Abstract A novel “tetra[benzo(18-crown-6)]-crowned cleft” ( 2 ) and two new “bis[benzo(15-crown-5)]-crowned clefts” ( 3 and 4 ) have been synthesized. Their respective selectivities in (i) alkali metal picrate extraction into chloroform and (ii) alkali metal perchlorate transport across bulk chloroform membranes have been determined relative to those of appropriate model compounds in each case. The observed picrate extraction selectivity order for 2 , i. e. Cs + > Rb + > K + > Na + > Li + , strongly suggests the existence of “sandwich” complexes which result from extraction cooperativity between two spatially proximate benzo(18-crown-6) units in 2 and a guest alkali metal cation. Interestingly, the corresponding selectivity order for 3 and 4 suggests that only 1 : 1 metal ion-crown ether complexes are formed. For bulk chloroform membranes, bis- and tetra-crowned clefts exhibit much more efficient transport of certain alkali metal perchlorates than do model mono-crown ether compounds.

Synthesis and alkali metal picrate extraction capabilities of a 4-oxahexacyclo[5.4.1.02,6.03,10.05,9.08,11]dodecane-derived cryptand. A new ionophore for selective ion complexation

Abstract The synthesis of a novel cage-functionalized cryptand, 5 , and the X-ray crystal structure of its 1:1 complex with Na + , i.e. 4 , are reported. Host molecule 5 displays high avidity toward Na + and K + picrates and appears to extract these cations selectively. The X-ray crystal structure of 4 clearly indicates that Na + is bonded to all seven Lewis base centers (i.e., nitrogen and oxygen atoms) in the complex. In addition, the corresponding alkali metal picrate extraction profile was obtained for 10 , an adamantane-containing analog of 5 . With the possible exception of its ability to extract K + picrate, there appears to be relatively little difference between the alkali metal picrate extracting capabilities of host molecule 10 and a corresponding monocyclic model system, i.e., N , N ′-diethyl-4,13-diaza-18-crown-6 ( 6 ).

Synthesis and alkali metal picrate extraction capabilities of novel, cage-functionalized diazacrown ethers. Effects of host preorganization on avidity and selectivity toward alkali metal picrates in solution

Abstract The synthesis of a series of cage-functionalized bis(monoazacrown) ethers and bis(diaza-crown) ethers is described. Alkali metal picrate extraction profiles have been determined for several members of this novel series of ionophores. The increased level of preorganization achieved when a cage-functionalized bis(diaza-crown) ether is incorporated into a “molecular box” results in higher levels of avidity and selectivity of the resulting host system toward alkali metal picrates in solution.

Generation and trapping of a caged cyclopentylidenecarbene

The reactive intermediate that is produced both (i) via reaction of 8-(dibromomethylene)-pentacyclo[5.4.0.02,6.03,10.05,9]unndecane (6) with n-BuLi-THF and (ii) via the corresponding reaction of pentacyclo[5.4.0.02,6.03,10.05,9]undecan-8-one (11) with diethyl diazomethylphosphonate (DAMP) has been shown to be vinylidenecarbene 7a rather than the corresponding cycloalkyne, 7b.

Synthesis, characterization and crystal density modeling of polycarbocyclic oxiranes

Abstract Polycyclic bis-epoxides 5, 6, and 7 have been synthesized, and their structures established unequivocally via application of single crystal X-ray crystallographic methods. The crystal densities of 2–7 (calculated from X-ray crystallographic data) are compared with the results of theoretical density predictions.

Acid and base promoted rearrangements of Hexacyclo[11.2.1.02,12.05,10.05.15.010,14]hexadeca-6,8-diene-4,11-dione

Abstract Hexacyclo[11.2.1.02,12.05,10.05,15.010,14]hexadeca-6,8-diene-4,11-dione (3) was synthesized via ring-expansion of hexacyclo[10.2.1.02,11.04,9.04,14.09,13]pentadeca-5,7-diene-3,10-dione (1). Reaction of a toluene solution of 3 with a catalytic amount of HCl resulted in extensive skeletal rearrangement, thereby affording 6,7-benzotetracyclo[7.3.0.04,12.05,10]dodecane-2,6-dione (4). Subsequent reaction of 4 with 3,6-diphenyl-1,2,4,5-tetrazine (5) afforded a novel molecular cleft, 6. Compound 3 reacted smoothly with ethanolic KOH at ambient temperature (in 3 h) or at reflux (in 0.5 h) to afford a rearranged product, 7. The structures of 3, 4, 5, and 7 were established unequivocally via application of single crystal X-ray crystallographic methods.

Nucleophilic additions of primary and secondary amines to pentacyclo[5.4.0.02,6.03,10.05,9]undecane-8,11-dione

The crystal structures of three compounds formedvia nucleophilic attack of a heterocyclic secondary amine on PCU-8,11-dione, with the concomitant intramolecular attack of one keto oxygen on the carbon of the other ketone, are presented. In all three compounds, the bridging oxygen contains substantial p-character, and the bonds to the “attacking” nitrogen are significantly shorter than would be expected.

Thermodynamic vs. kinetic control in the Diels-Alder cycloaddition of cyclopentadiene to 2,3-dicyano-p-benzoquinone

Diels-Alder cycloaddition of cyclopentadiene (1a) to 2,3-dicyano-p-benzoquinone (2a), when performed in methanol solvent at ambient temperature, proceeds with kinetic control to afford 1α,4α,4aβ,8aβ-tetrahydro-5,8-dioxo-1,4-methanonaphthalene-4a,8a-dicarbonitrile (7, 77% yield). However, when this cycloaddition is performed by refluxing an equimolar solution of1a and2a in benzene for 3 h, the product of thermodynamic control, i.e., 1α,4α,4aα,8aα-tetrahydro-5,8-dioxo-1,4-methanonaphthalene-6,7-dicarbonitrile (3a) is obtained in 64% yield. The structure of3a was confirmed by an analysis of the reduced intramolecular photocyclization product,9.

Intermolecular vs. Intramolecular carbene reactions of a cage-functionalized cyclopentylcarbene

Abstract The results of carbene reactions of pentacyclo[5.4.0.0 2,6 .0 3,10 .0 5,9 ]undecan-8-ylidene (i.e., PCU-8-ylidene, 9 ), generated under different conditions by using different precursors [i. e., (i) sodium salt of PCU-8-one p -tosylhydrazone ( 8 ), (ii) PCU-8-diazirine ( 11 ), and (iii) 8,8-dibromo-PCU ( 12 )], are reported. PCU-8-carbene ( 9 ), generated thermally from 8 , afforded homopentaprismane ( 17 , 9.6% yield) via intramolecular C-H insertion along with other reaction products. By way of contrast, photodecomposition of 11 afforded a mixture of isomeric azines, 21a–21d , as the major reaction product. No intramolecular carbene trapping products were obtained when 9 was generated via reaction of 12 with n -BuLi.