Rearrangement Reactions of Tritylcarbenes: Surprising Ring Expansion and Computational Investigation

Abstract

As a rule, acetylides and sulfonyl azides do not undergo electrophilic azide transfer because 1,2,3-triazoles are usually formed. We show now that treatment of tritylethyne with butyllithium followed by exposure to 2,4,6-triisopropylbenzenesulfonyl azide leads to products that are easily explained through the generation of short-lived tritylethynyl azide and its secondary product cyanotritylcarbene. Furthermore, it is demonstrated that tritylcarbenes generally do not produce triphenylethenes exclusively, as was stated in the literature. Instead, these carbenes always yielded also (diphenylmethylidene)cycloheptatrienes (heptafulvenes) as side products. This result is supported by static DFT, coupled cluster, and ab initio molecular dynamics calculations. From these investigations, the fused bicyclobutane intermediate was found to be essential for heptafulvene formation. Although the bicyclobutane is also capable of rearranging to the triphenylethene product, only the heptafulvene pathway is reasonable from the energetics. The ethene is formed straight from cyanotritylcarbene.

More Stable Template Localization for an Incremental Focal-Point Approach—Implementation and Application to the Intramolecular Decomposition of Tris-perfluoro-tert-butoxyalane

“…For instance, we could not treat cyanotritylcarbene as well as the transition state of its formation from tritylethynyl azide (see Figure ). Both are key intermediates in an experimentally and computationally investigated rearrangement reaction . With our new implementation of the incremental scheme, we were able to compute the CCSD­(T)­(F12*) energies for these structures and therefore complete the corresponding reaction profile.…”

“…Both are key intermediates in an experimentally and computationally investigated rearrangement reaction. 175 With our new implementation of the incremental scheme, we were able to compute the CCSD(T)(F12*) energies for these structures and therefore complete the corresponding reaction profile. A part of these complemented energetics is shown in Figure 7.…”

Synthesis, Characterization and Reactions of (Azidoethynyl)trimethylsilane

“…The synthesis of this short-lived compound is easily performed if appropriate substrate, reagent and reaction conditions are used. Because in situ generation of azidoacetylenes has recently been utilized to prepare a variety of products via the decomposition to the corresponding cyanocarbenes [11,13,[28][29][30][31], the decay of 6 or similar silylethynyl azides to give cyano(silyl)carbenes may be useful in organic synthesis, especially since the latter carbenes are, to the best of our knowledge, unknown in literature.…”