Depending on the reaction conditions and the nature of substituents at the triple bond, anionic cyclizations of hydrazides of o-acetylenyl benzoic acids can be selectively directed along three alternative paths, each of which provides efficient access to a different class of nitrogen heterocycles. The competition between 5-exo and 6-endo cyclizations of the "internal" nitrogen nucleophile is controlled by the nature of alkyne substituents under the kinetic control conditions. In the presence of KOH, the initially formed 5-exo products undergo a new rearrangement that involves a ring-opening followed by recyclization to the formal 6-exo-products and rendered irreversible by a prototropic isomerization. DFT computations provide insight into the nature of factors controlling relative rates of 5-exo, 6-endo, and 6-exo cyclization paths, ascertain the feasibility of direct 6-exo closure and relative stability for the anionic precursor for this process, provide, for the first time, the benchmark data for several classes of anionic nitrogen cyclizations, and dissect stereoelectronic effects controlling relative stability of cyclic anionic intermediates and influencing reaction stereoselectivity. We show that the stability gain due transformation of a weak pi-bond into a stronger sigma-bond (the usual driving force for the cyclizations of alkynes) is offset in this case by the transformation of a stable nitrogen anion into an inherently less stable carbanionic center. As a result, the cyclizations are much more sensitive to external conditions and substituents than similar cyclizations of neutral species. However, the exothermicity of such anionic cyclizations is increased dramatically upon prototropic isomerization of the initially formed carbanions into the more stable N-anions. Such tautomerizations are likely to play the key role in driving such cyclizations to completion but may also prevent future applications of such processes as the first step in domino cyclization processes.

Triarylmethanols – the direct precursors of persistent trityl radicals – are racemic mixtures of chiral three-bladed molecular propellers. Depending on bulkiness of aryl groups they exhibit various liabilities to interconversion, the half- life time of room temperature racemization varying in a range between 8.4 hours and 1.32 years. NOESY/EXSY experiment performed on two representative models strongly supports the two-ring flip mechanism for the configurational interchange.

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This work analyzes multiple new reaction pathways which originate from intramolecular reactions of activated alkynes with the appropriately positioned multifunctional hemiaminal moiety. Combination of experimental substituent effects with Natural Bond Orbital (NBO) analysis revealed that alkyne polarization controls partitioning between these cascades. A particularly remarkable transformation leads to the formation of six new bonds at the two alkyne carbons due to complete disassembly of the alkyne moiety and formal insertion of a nitrogen atom between the two acetylenic carbons of the reactant. This reaction offers a new synthetic approach for the preparation of polycyclic aromatic amides with a number of possible applications in molecular electronics. Another of the newly discovered cascades opens access to substituted analogues of Sampangine alkaloids which are known for their antifungal and antimycobacterial activity against AIDS-related opportunistic infection pathogens.