Azoarene activation for Schmidt-type reaction and mechanistic insights

The Schmidt rearrangement, a reaction that enables C-C or C-H σ bond cleavage and nitrogen insertion across an aldehyde or ketone substrate, is one of the most important and widely used synthetic tools for the installation of amides and nitriles. However, such a reaction frequently requires volatile, potentially explosive, and highly toxic azide reagents as the nitrogen donor, thus limiting its application to some extent. Here, we show a Schmidt-type reaction where aryldiazonium salts act as the nitrogen precursor and in-situ-generated cyclopenta-1,4-dien-1-yl acetates serve as pronucleophiles from gold-catalyzed Nazarov cyclization of 1,3-enyne acetates. Noteworthy is that cycloketone-derived 1,3-enyne acetates enabled ring-expansion relay to access a series of 2-pyridone-containing fused heterocycles, in which nonsymmetric cycloketone-derived counterparts demonstrated high regioselectivity. Aside from investigating the scope of this Schmidt-type reaction, mechanistic details of this transformation are provided by performing systematic theoretical calculations.

Iminologous epoxide ring-closure

The discovery of new reactions enables chemists to attain a better understanding of fundamental chemical reactivity and push the boundaries of organic synthesis. Our understanding and manipulation of high-energy states such as reactive conformations, intermediates, and transition structures contribute to this field. Herein we interrogate epoxide ring-closure by inserting the C[double bond, length as m-dash]N functionality into a well-known precursor to nucleophilic epoxide ring-closure. The synthesis of tetrasubstituted, nitrile-tethered epoxides takes place via activation of iminologous diols followed by fragmentation. Mechanistic study reveals the transformation to be stereospecific, which is consistent with the concerted nature of the epoxide ring-closure.

Nitromethane as a nitrogen donor in Schmidt-type formation of amides and nitriles

The Schmidt reaction has been an efficient and widely used synthetic approach to amides and nitriles since its discovery in 1923. However, its application often entails the use of volatile, potentially explosive, and highly toxic azide reagents. Here, we report a sequence whereby triflic anhydride and formic and acetic acids activate the bulk chemical nitromethane to serve as a nitrogen donor in place of azides in Schmidt-like reactions. This protocol further expands the substrate scope to alkynes and simple alkyl benzenes for the preparation of amides and nitriles.