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.

The reduction of Bcyanonnthracene by two equivalents of potassium in liquid ammonia was shown to yield the 9cyanoanthracene dianion, whereas 1-naphtho-and benzonitrile gave the cyanodihydroaryl anions corresponding to the protonation of nitrile dianions at a position para to the cyano group. The 9-cyanoanthracene dianion underwent the same transformation in the presence of a stronger protonating agent, methanol. According to I3C NMR spectral data of the generated species, the cyano group extracts the negative charge from the *-electronic system: ca 0.20:0*25 e in the case of the 9-cyanoanthracene dianion and ca 0-140.17 e in the case of cyanodihydroaryl anions. These estimations and the general NMR pattern of r-charge distribution in all the anionic species under investigation are in accordance with data from quantum molecular orbital calculations at the PM3 and INDO levels, being reflected by the fairly good linear relationships between the changes of ring carbon chemical shifts on going to the anionic species from the respective neutral precursors on the one hand and the calculated nsharges on the other. The para-orienting effect of the cyano group in the protonation of nitrile dinnions is discussed in terms of the r-charge distribution in the starting dianion and the tendency to form a most stable cyanodihydroaryl anion isomer. RESULTSThe reduction was performed just before recording NMR spectra by adding two equivalents of potassium 'Part5 of the series 'Reductive Alkylation of Arenes.' For Parts 1-4, see Refs 1 and 2. t Present address:

Betulinic acid–peptide conjugates exhibit high anti-inflammatory activity.

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The electronic and geometric structural changes of acetone upon protonation are studied by 3C NMR spectroscopy and by molecular orbital (MO) calculations using the LORG (local orbital/local origin) method to calculate chemical shieldings and the CLOPPA (contributions for localized orbitals within the polarised propagator approach) analysis of the J coupling constants. In protonated acetone the 13C NMR spectrum has been resolved and two different methyl resonances (1.2 ppm apart) have been assigned. The one-bond C-C coupling constants