Saturated five-membered nitrogen heterocycles reactions

In a study of synthetic routes to the phorbol class of compounds, Lautens cyclised the stannane 307 (with 5 equiv MeLi, to avoid stannane reincorporation) to the 7,5-fused ring system 3 0 8.138 This reaction also works in the synthesis of analogous saturated five-membered nitrogen and sulfur heterocycles (see below). 

Hydrolysis of imidazolylidenes has been studied by DFT calculations and NMR experiments. The outcome of the reaction has been shown to be highly dependent on the amount of water involved in the reaction, and an equilibrium between the carbene and hydroxide ion has been identified. Related to this study, the pAT s of a range of NHCs have been determined via deuterium exchange experiments monitored by H NMR and found to increase markedly with electron donation from nitrogen substituents. Saturation was found to have only minor influence on the acidity of the flve-membered heterocycles. In contrast, the ring size has a major influence (moving from five- to six-membered heterocycles raised the pAT by up to 5 units). 

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