RICONThe Computer Program for the Quantitative Investigations of Cyclic Organic Molecule Conformations

symm-Tetramethylenecyclooctane: en route to polyspirocycles

A straightforward gram-scale synthesis of 1,3,5,7-tetrakis(methylidene)cyclooctane (TMCO) from commercial adamantane-1,3-dicarboxylic acid has been developed. TMCO exhibits high reactivity toward a number of carbenes and epoxidizing reagents, undergoing multiple cyclopropanations, dihalocyclopropanations, or epoxidations of four double bonds to yield polyspirocyclic products. Stereochemical features of polyspirocyclopropanated compounds have been thoroughly examined in experimental (NMR) and theoretical (DFT) studies. Comprehensive stereochemical assignment of TMCO adducts with dihalocarbenes and spiroepoxy products was achieved. The conditions of the formation of 1-methyl-3,7-bis(methylidene)bicyclo[3.3.1]nonane from the adamantane derivative were optimized, and diadducts of this diene with dihalocarbenes were isolated and characterized.

The dynamics of the conformational changes in the hexopyranose ring: a transition path sampling approach

The transition paths corresponding to the conformational rearrangements in the ring of hexapyranose (α-d- and β-d-glucose) molecules were described by applying the transition path sampling method.

Two seven-membered heterocycles with 1,2-diaza ring N atoms: 3,5,7-triphenyl-1,2-diazacyclohepta-1(7),2-diene and 3,7-bis(2-hydroxyphenyl)-5-phenyl-1,2-diazacyclohepta-1(7),2-diene

The title compounds, 3,5,7-triphenyl-1,2-diazacyclohepta-1(7),2-diene, C23H20N2, (I), and 3,7-bis(2-hydroxyphenyl)-5-phenyl-1,2-diazacyclohepta-1(7),2-diene, C23H20N2O2, (II), constitute the first structurally characterized examples of seven-membered heterocycles with 1,2-diaza ring N atoms. Compound (I) crystallizes in the space groupP\overline{1}, with two independent molecules in the asymmetric unit that differ in the conformation of one of the phenyl rings, while (II) crystallizes in the space groupC2/c. The C5N2ring in each of (I) and (II) adopts a twist-boat conformation. Compound (I) exhibits neither C—H...π interactions nor π–π stacking interactions, whereas (II) shows both intramolecular O—H...N hydrogen bonds and a C—H...π interaction that joins the molecules into an infinite chain in the [010] direction.

Computerized molecular modeling of carbohydrates

Computerized molecular modeling continues to increase in capability and applicability to carbohydrates. This chapter covers nomenclature and conformational aspects of carbohydrates, perhaps of greater use to carbohydrate-inexperienced computational chemists. Its comments on various methods and studies might be of more use to computation-inexperienced carbohydrate chemists. New work on intrinsic variability of glucose, an overall theme, is described.

Total Synthesis, Molecular Editing and Evaluation of a Tripyrrolic Natural Product: The Case of “Butylcycloheptylprodigiosin”

Conflicting reports are found in the literature on whether the ortho-pyrrolophane derivative 6, which has been named "butylcycloheptylprodigiosin" even though it is a cyclononane derivative, is a natural product or merely a mis-assigned structure. This dispute has now been resolved by an unambiguous total synthesis of this complex alkaloid which confirms the initial structure assignment. The chosen approach is largely catalysis-based, featuring the first application of a "Narasaka-Heck" reaction in natural product chemistry. This palladium-catalyzed transformation allows the unsaturated oxime ester 26 to be converted into the bicyclic dihydropyrrole 27. Other notable reactions of the reported approach to 6 are a regioselective Tsuji-Trost reaction of the doubly allylic acetate 21 with methyl acetoacetate, a base-induced aromatization of 27 to the corresponding pyrrole 28, a chemoselective oxidation of the benzylic methyl group in 33 with cerium ammonium nitrate in a biphasic reaction medium that does not affect the labile pyrrole nucleus, and a Suzuki cross-coupling for the completion of the heterocyclic domain. Diversification in the latter step leads to a set of analogues that differ from the natural product in the terminal (hetero)arene ring. This structural modification results in complete loss of the very pronounced ability of the parent compound 6 to induce oxidative cleavage in double stranded DNA in the presence of Cu(II). Several cyclononane-, cyclononene- and cyclononadiene derivatives prepared en route to 6 have been characterized by crystal structure analysis, allowing the conformational behavior of nine-membered carbocycles to be studied.