The presence of a nearby tethered functional group (G, G = tertiary amide or amine) can significantly impact the rate of cleavage of an Si−O bond. We report here an in situ 1 H NMR spectroscopic investigation of the relative rates of cleavage of model substrates containing two different Si−O substructures, namely alkoxydisiloxanes [GRO−Si(Me 2 )−O−SiMe 3 ] and carbodisiloxanes [GR−Si(Me 2 )−O−SiMe 3 ]. The trends in the relative rates (which slowed with increasing chain length, with a notable exception) of alkoxydisiloxane hydrolyses were probed via computation. The results correlated well with the experimental data. In contrast to the hydrolysis of the alkoxydisiloxanes, the carbodisiloxanes were not fully hydrolyzed, but rather formed an equilibrium mixture of starting asymmetric disiloxane, two silanols, and a new symmetrical disiloxane. We also uncovered a facile siloxy-metathesis reaction of an incoming silanol with the carbodisiloxane substrate [e.g., Me 2 NR−Si(Me 2 )−O−SiMe 3 + HOSiEt 3 ⇋ Me 2 NR−Si(Me 2 )−O−SiEt 3 + HOSiMe 3 ] facilitated by the pendant dimethylamino group, a process that was also probed by computation.

Arylhydrazines (ArNαHNβH2) are ambident nucleophiles. We describe here their reactivity with benzynes generated in situ by thermal cyclization of several multiynes. Products arising from attack of both the alpha- and beta-nitrogen atoms are observed. These competitive modes of reaction were explored by DFT calculations. Substituent effects on the site-selectivity for several substituted phenylhydrazines were explored. Interestingly, the hydrazo products from beta-attack (ArNHNHAr′) can be oxidized, sometimes in situ by oxygen alone, to give structurally complex, unsymmetrical azoarenes (ArNNAr′). Toluenesulfonohydrazide and benzohydrazide analogues were each demonstrated to undergo similar transformations, including oxidation to the corresponding benzyne-trapped azo compounds.

o-Benzynes can be utilized to construct heterocyclic motifs using various nucleophilic and cycloaddition trapping reactions. Acridines have been synthesized by capture of C,Ndiarylimines with benzynes generated by classical methods (i.e., from ortho-elimination of precursor arene compounds), although in poor yields. We report here that these imines can be [a] Scheme 1. Previous studies of reactions of benzynes with imines in either (a) a net [2+2] pathway or (b) a [4+2] pathway.

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E- vs. Z-azobenzenes engage benzynes in complementary fashion, producing either dihydrophenazine or N-aminocarbazole skeletons, respectively. DFT and experimental mechanistic studies shed light on why.