Ram P. Kashyap

Tetrathiafulvalene quinones, hydroquinones and esters

Abstract Benzocyclohexa-2,5-diene-1,4-dione-1,3-thiole-2-thione (2) was synthesized starting with 2,3-dichloronapthoquinone (1). Compounds 3 and 4 were also obtained; however, the yield of 2 can be increased through control of the temperature and reaction time. Reaction of 2 with triethylphosphite gave 5 and the tetrathiafulvalene ester 6. The tetrathiafulvalenequinone (9) was obtained by hydrolysis of 6 followed by oxidation of 8. Compound 9 was obtained more directly by hydrogenation of 2 followed by coupling with triethylphosphite and oxidation. Chloranil was used to prepare the dithiafulvene quinone 12 which was reduced, coupled with triethylphosphite to form, presumably , polymer 13. The reactions were repeated using the hexanoic acid esters of the corresponding hydroquinone thiafulvalenes. The crystal structures of 2, 3, 4, 5, 6a and 10 were determined by X-ray diffraction. Cyclic voltammetry studies show the tetrathiafulvalene quinones reduce like quinones, but do not exhibit the oxidation properties of tetrathiafulvalenes.

Intramolecular alkene-oxirane cycloadditions. Synthesis and structure of 5-oxapentacyclo [7.3.0.03,7.o4,12.06,10]dodecane-2,8-dione

Abstract MCPBA promoted epoxidation of the C(9)-C(10) double bond in endo -tricyclo [6.2.1.0 2,7 ]undeca-4, 9-diene-3,6-dione ( 4 ) followed by intramolecular [2 + 2] photocyclization of the resulting exo epoxide ( 5 ) afforded the title compound, 1 , in 16% overall yield. The structure of symmetrically hydrated 1 (i.e., 1a ) was determined by single crystal X-ray crystallographic methods. Proton and carbon-13 NMR spectral assignments are given for epoxide 5 .

Bis(dimethylphosphino)ethane substitution in PhCCo3(CO)9: Synthesis and X-ray structure of the phosphine-bridged cluster PhCCo3(CO)7(dmpe)

Abstract The bidentate phosphine ligand bis(dimethylphosphino)ethane (dmpe) reacts with PhCCo 3 (CO) 9 ( 1 ) to initially yield PhCCo 3 (CO) 7 (dmpe) ( 2 ). The dmpe ligand in 2 bridges adjacent cobalt centers in the equatorial plane as shown by FT-IR and 31 P NMR spectroscopy and single-crystal X-ray diffraction analysis. The phosphine-bridged cluster PhCCo 3 (CO) 7 (dmpe) crystallizes in the orthorhombic space group P 2 1 2 1 2 1 with a = 9.142(1), b = 16.140(2) c = 16.903(3) A, V = 2494.7(5) A 3 and Z = 4. Blockcascade least-squares refinement yielded R = 0.0702 for 2151 reflections. Reaction of 2 with additional dmpe is shown to yield the known cluster PhCCo 3 (CO) 5 (dmpe) 2 ( 3 ) as a result of dmpe chelation at the unsubstituted cobalt center in 2 . 31 P NMR analysis reveals that bridging dmpe in 2 undergoes an equatorial → axial rearrangement during the formation of 3 in agreement with the solid-state structure.

Diastereofacial selectivity in Diels-Alder cycloadditions of methyl acrylate to facially differentiated unsymmetrical Cyclohexa-1,3-dienes

Abstract The Diels-Alder cycloadditions of methyl acrylate to the unsymmetrical hexacyclo[10.2.1.02,11.04,14.09,13pentadecadienes 1b–f proceed with a high degree of π-facial stereoselectivity but only moderate regioselectivity. The results of fixed model transition state calculations, performed in an effort to establish the factors which control selectivity in these cycloadditions, are reported. Diels-Alder cycloadditions of methyl acrylate to the unsymmetrical hexacyclo[10.2.1.02,11.04,9.04.14.09,13]pentadecadienes 1b–f have been studied, and in each case the resulting [4 + 2] cycloadducts have been fully characterised. The addition reactions proceed with a high degree of π-facial stereoselectivity but with only a moderate level of regioselectivity. The observed π-facial selectivity is correctly predicted from BAE distributions of the ensemble of conformations from a conformational search employing a fixed model transition state. However for 1c, the model predicts that top face addition becomes marginally competitive and this is not reproduced in the experiment. The regioselective trends observed for bottom face addition are predicted similarly from BAE distributions of the ensemble of conformations from a conformational search employing a fixed model transition state. However, the balance of electrostatic vs. steric factors is not well reproduced for the small energy differences involved in the regioselection for the Diels Alder cycloadditions to 1b and 1c. Further insight into the subtle blend of steric and electronic factors which influence the regioselectivities of these Diels-Alder reactions awaits detailed theoretical analysis. Computational approaches designed to clarify these points are under way in our respective laboratories.

Structures of three substituted pentacyclo[5.4.0.02, 6.03, 10.05, 9]undecanes and a computational analysis of bond lengths

Abstract5-Methyl-2-phenylpentacyclo[5.4.0.02, 6.03, 10.05, 9]undecane-8, 11-dione,5-methyl-2-phenylpentacyclo [5.4.0.02,6.03,10.05,9]undecane-8-one-11-ol,and 5-methyl-2-phenylpentacyclo[5.4.0.02,6.03,10.05,9]undecane-8,11-diol are three cage compounds which differ only in the oxidation state at C(8) and C(11). The three compounds contain a four-membered, a six-membered, and four five-membered rings fused into a cagelike structure. An X-ray structure analysis shows the C(1)-C(7) and C(9)-C(10) bonds in the diketo cage to be 1.606(2) and 1.586(2) Å, which are significantly longer than in the other two molecules. In order to assess the effects of strain, steric, and electronic factors in these compounds, we investigated the unsubstituted parent cage compounds and a series of derivatives by molecular mechanics (MM3), AMPAC (AM1), MOPAC (PM3), and GAUSSIAN 90 calculations. These data suggest that dipolar through space interactions are responsible for the bond elongation and not aπ−→σ* interaction, which has been postulated in parallelπ-systems originating from a common bond. A small degree ofπ−→σ* “through-bond” interaction may contribute to the lengthening in the dimethylene cage analogues.

Synthesis of Novel Heterocyclic Clefts Derived from Tetracyclo[6.3.0.04,11.05,9]undecane-3,6-dione and Tricyclo[6.3.0.02,6]ubdecane-3,11,dione

New molecular clefts dipyridazinotricycloundecane derivatives (6a-6c), (9a), and (9b) have been prepared via base promoted reactions of 3,6-di -aryl-1,2,4,5-tetrazines with tetracyclo[6.3.0.0 4,11 .0 5,9 ]unde- cane-3,6-dione (1) and with tricyclo [6.3.0.0 2,6 ]undecane-3,11-dione (10), respectively. Compounds of this type are of interest as a poten- tial new class of host molecules for use in host-guest complexation studies (i.e., inclusion phenomena and molecular recognition). The re- sults obtained via studies of the solution electrochemistry of systems (6a-6c), (9a), and (9b) afforded no evidence for the existence of any significant electronic interaction between opposing «arms» in these molecular clefts

Thiele's ester as a reagent in organic synthesis. Preparation of pentacyclo[5.4.0.02,5.03,10.04,8]undecane-10-carboxylic acid

Abstract Succinyl cleavage of the C(2)–C(5) σ-bond in dimethyl pentacyclo[5.3.0.0 2,5 .0 3,9 .0 4,8 ]decane-2,5-dicarboxylate, 2 , afforded a tetracyclic diester, 3 (22–26%), along with two minor reaction products ( 4 and 5 ). Dieckmann condensation of 3 produced a mixture of 6a and 6b (67%). Wolff-Kishner reduction of the mixture of 6a and 6b thereby obtained afforded a mixture of products from which the title compound, 7b , could be isolated in 63% yield by fractional recrystallization. The structures of 3 , 4 and 7b were established unequivocally via X-ray crystallographic methods.

Cavity-shaped molracs with inward-facing, direct line-of-sight functionality

Abstract New rigid cavity molecules are described in which bromides, epoxides, olefins, alcohols and acetates are positioned such that there is direct line of sight between them. Examples are provided of systems where the separation distances are in the range from 4–7 A, although the principles espoused allow production of molecules with significantly larger separation.

Amino acid complexes of [Co(III) (trien)]+3

Seven β2 complexes have been investigated and the structural parameters compared with literature values and molecular mechanics calculations. All β2 compounds exhibit the (S,S,λλδ) or, (R,R,δδλ) configuration. Three of the β2 complexes have monocoordinated amino acids or amino acid esters while the amino acid is chelated in the others. The Co−N bondtrans to the amino acid oxygen or a Cl− varies significantly in length due to thetrans-effect. The chelate rings are twisted to minimize torsional interactions and the changes in conformation in the various structures can be modeled by molecular mechanics. In one complex the carbonyl groups of enantiomeric complexes are bridged by silver ions. In β2[Co(trien)(C-formylglycine)]Cl2 · H2O the carbonyl oxygen of the chelated amino acid is protonated and the formyl group exists in the enol form.

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.