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A new flexible implementation of a genetic algorithm for locating unique low energy minima of isomers of clusters is described and tested. The strategy employed can be applied to molecular or atomic clusters and has a flexible input structure so that a system with several different elements can be built up from a set of individual atoms or from fragments made up of groups of atoms. This cluster program is tested on several systems, and the results are compared to computational and experimental data from previous studies. The quality of the algorithm for locating reliably the most competitive low energy structures of an assembly of atoms is examined for strongly bound Si-Li clusters, and ZnF2 clusters, and the more weakly interacting water trimers. The use of the nuclear repulsion energy as a duplication criterion, an increasing population size, and avoiding mutation steps without loss of efficacy are distinguishing features of the program. For the Si-Li clusters, a few new low energy minima are identified in the testing of the algorithm, and our results for the metal fluorides and water show very good agreement with the literature.

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Studies directed at the synthesis of lamellarin G trimethyl ether and ningalin B via vinylogous iminium salt derivatives are described. The successful strategy relies on the formation of a 2,4-disubstituted pyrrole or a 1,2,3,4-tetrasubstituted pyrrole from a vinylogous iminium salt or vinylogous iminium salt derivative. Subsequent transformations of these highly substituted pyrroles lead to efficient and regiocontrolled formal syntheses of the respective pyrrole containing natural products.

The Bergman cyclization is an important reaction in which an enediyne cyclizes to produce a highly reactive diradical species, p-benzyne. Enediyne motifs are found in natural antitumor antibiotic compounds, such as calicheammicin and dynemicin. Understanding the energetics of cyclization is required to better control the initiation of the cyclization, which induces cell death. We computed the singlet and triplet potential energy surfaces for the Bergman cyclization of (Z)-hex-3-ene-1,5-diyne using the CCSD and EOM-SF-CCSD methods. The triplet enediyne and transition state were found to have C 2 symmetry, which contrasts with the singlet reactant and transition state that possess C 2v symmetry. We analyzed the frontier orbitals of both cyclization pathways to explain the large energetic barrier of the triplet cyclization. Reaction energies were calculated using CCSD­(T)/cc-pVTZ single-point calculations on structures optimized with CCSD/cc-pVDZ. The singlet reaction was found to be slightly endothermic (ΔH rxn = 13.76 kcal/mol) and the triplet reaction was found to be highly exothermic (ΔH rxn = −33.29 kcal/mol). The adiabatic singlet−triplet gap of p-benzyne, computed with EOM-SF-CCSD/cc-pVTZ, was found to be 3.56 kcal/mol, indicating a singlet ground state.