Alan D. Payne

Practical Synthesis of the Dendralene Family Reveals Alternation in Behavior

Back from obscurity: The practical synthesis of the first six members of the fundamental class of acyclic branched oligoalkenes has been achieved. The syntheses allow access to the target compounds on multigram scales in good yields. Members of the family with even numbers of double bonds are significantly more stable than those with odd numbers (see picture), and exhibit different chemical reactivities in Diels-Alder reactions.

Practical Synthesis and Reactivity of [3]Dendralene

A convenient and high-yielding three-step synthesis of the simplest branched triene, [3]dendralene, has been devised. The synthesis is robust and operationally simple, requiring no chromatography and involving no protecting groups or specialized equipment, allowing the synthesis of the volatile hydrocarbon in pure, solvent free form on a multigram scale. The stability, dimerization when stored neat, and Diels-Alder reactivity of [3]dendralene--including double cycloaddition sequences and catalytic enantioselective variant--are reported.

Synthesis and properties of the ivyanes: the parent 1,1-oligocyclopropanes

Practical syntheses of the first six members of the ivyane (1,1-oligocyclopropane) family of fundamental hydrocarbons have been achieved from the cross-conjugated polyenes known as dendralenes. Evidence for helical conformations in both the solid state and in solution is presented. [6]Ivyane exhibits one of the highest experimental heats of combustion recorded for a hydrocarbon. Ring-opening reactions of ivyanes furnish new and interesting structures that are difficult to access by conventional means.

Accurate Coordinates and 2MASS Cross Identifications for (Almost) All Gliese Catalog Star

We provide precise J2000, epoch 2000 coordinates, and cross-identifications to sources in the 2MASS Point Source Catalog for nearly all stars in the Gliese, Gliese-Jahreiss, and Woolley catalogs of nearby stars. The only Gliese objects where we were not successful are two Gliese sources that are actually QSOs; two proposed companions to brighter stars, which we believe do not exist; four stars included in one of the catalogs but identified there as only optical companions; one probable plate flaw; and two stars that simply remain unrecovered. For the 4251 recovered stars, 2693 have coordinates based on Hipparcos positions, 1549 have coordinates based on 2MASS data, and 9 have positions from other astrometric sources. All positions have been calculated at epoch 2000 using proper motions from the literature, which are also given here.

Synthesis and Diels–Alder Reactivity of Substituted [4]Dendralenes

The first synthesis of all five possible monomethylated [4]dendralenes has been achieved via two distinct synthetic strategies. The Diels-Alder chemistry of these new dendralenes (as multidienes) with an electron poor dienophile, N-methylmaleimide (NMM), has been studied. Thus, simply upon mixing the dendralene and an excess of dienophile at ambient temperature in a common solvent, sequences of cycloadditions result in the rapid generation of complex multicyclic products. Distinct product distributions are obtained with differently substituted dendralenes, demonstrating that dendralene substitution influences the pathway followed, when a matrix of mechanistic possibilities exists. Dendralene site selectivities are traced to electronic, steric and conformational effects, thereby allowing predictive tools for applications of substituted dendralenes in future synthetic endeavors.

A Combined computational-experimental study of the kinetics of intramolecular Diels - Alder reactions in a series of 1,3,8-nonatrienes

Activation enthalpies for a series of five 1,3,8-nonatriene intramolecular Diels–Alder (IMDA) reactions involving substrates 1–5 have been determined experimentally and Singleton’s natural abundance method has been employed to determine kinetic isotope effects in the IMDA reaction of fumarate 3. The activation enthalpies for the IMDA reactions of the systems possessing a –CH2OCH2– diene/dienophile tether are significantly smaller than their counterparts possessing the –CH2OC(=O)– tether. The experimental activation enthalpies have been used to benchmark computed values from four model chemistries, namely two density functional theory functionals, B3LYP and M06-2X, and two generally very accurate composite ab initio wave function methods, CBS-QB3 and G4(MP2). G4(MP2) outperformed the computationally more expensive CBS-QB3 method, but the vastly cheaper M06-2X/6-31G(d)//B3LYP/6-31G(d) method was sufficiently accurate to be the recommended method of choice for calculating activation parameters. Experimental 2H kinetic isotope effects for the IMDA reaction of fumarate 3 confirmed the computational predictions that this Diels–Alder reaction is concerted but asynchronous.