Synthetic Doping of Diamondoids through Skeletal Editing

Theoretical determination of the standard enthalpies of formation of alkyl radicals using the concept of a complete set of homodesmotic reactions

The complete sets of homodesmotic reactions (HDR) for 107 acyclic alkyl free radicals С4-С9 of normal and branched structure were constructed using the graph-theoretic representation and analysis of a tested compound. The absolute enthalpies of the studied compounds and HDR reference structures were calculated using the M062X/cc-pVTZ level of theory. Based on these data, the thermal effects of HDRs were calculated and then applied to determine the standard enthalpies of formation of the studied radicals using the known enthalpies of formation of reference structures. The dissociation energies of BDE C-H and C-CH3 bonds were also calculated. The effect of radical structure on the BDE value is discussed, and a new effect of stabilization of the radical center in the skewed conformation of free radical is established; this effect has not been previously described in the scientific literature.

Heat Capacity Estimation Using a Complete Set of Homodesmotic Reactions for Organic Compounds

Reliable information about isobaric heat capacities C_P is necessary to determine the energies of organic compounds and chemical processes at an arbitrary temperature. In this work, the possibility of theoretical estimation of C_P by the homodesmotic method is analyzed. Three cases of C_P calculation applying the methodology of the complete set of homodesmotic reactions (CS HDRs) are considered: the gas- and liquid-phase C_P of organic compounds of various classes at 298 K (the mean absolute value of reaction heat capacity, MA ΔC_P = 1.44 and 2.83 J/mol·K for the gas and liquid phase, correspondingly); and the gas-phase C_P of n-alkanes C₂-C₁₀ in the temperature range of 200-1500 K with an average error in calculating the heat capacity of 0.93 J/mol·K. In the latter case, the coefficients of the Shomate equation are determined for all n-alkanes that satisfy the homodesmoticity condition. New values of gas- and liquid-phase heat capacities are obtained for 41 compounds. The CS HDRs-based approach for estimating the C_P of organic compounds is characterized by high accuracy, which is not inferior to that of the best C_P-additive schemes and allows us to analyze the reproducibility of the calculation results and eliminate unreliable reference data.

Borylated Cyclopropanes as Spring-Loaded Entities: Access to Vicinal Tertiary and Quaternary Carbon Stereocenters in Acyclic Systems

Herein, we present the formation of acyclic frameworks bearing two consecutive stereocenters of either tertiary or quaternary nature starting from easily accessible cyclopropenes. This holistic approach involves a regio- and diastereoselective hydro- or carboborylation of substituted cyclopropenyl esters. Formation of boronate complexes of the latter via the addition of nucleophiles and subsequent stereospecific 1,2-migration with carbon–carbon bond cleavage delivered the title compounds.

Recent ring distortion reactions for diversifying complex natural products

Covering: 2013-2022.Chemical diversification of natural products is an efficient way to generate natural product-like compounds for modern drug discovery programs. Utilizing ring-distortion reactions for diversifying natural products would directly alter the core ring systems of small molecules and lead to the production of structurally complex and diverse compounds for high-throughput screening. We review the ring distortion reactions recently used in complexity-to-diversity (CtD) and pseudo natural products (pseudo-NPs) strategies for diversifying complex natural products. The core ring structures of natural products are altered via ring expansion, ring cleavage, ring edge-fusion, ring spiro-fusion, ring rearrangement, and ring contraction. These reactions can rapidly provide natural product-like collections with properties suitable for a wide variety of biological and medicinal applications. The challenges and limitations of current ring distortion reactions are critically assessed, and avenues for future improvements of this rapidly expanding field are discussed. We also provide a toolbox for chemists for the application of ring distortion reactions to access natural product-like molecules.