Donor–Acceptor–Acceptor 1,3-Bisdiazo Compounds: An Exploration of Synthesis and Stepwise Reactivity

Abstract

Metal carbenes, derived from the decomposition of diazo compounds, are valued for their capacity to perform a variety of transformations. A unique class of acyclic, bis-diazo compounds, the donor–acceptor–acceptor 1,3-bisdiazo compounds, are described herein. These compounds are available from acyclic β-keto esters and especially reactive at the donor–acceptor diazo unit. These bisdiazo compounds react smoothly with rhodium acetate and alcohols to give monodiazo, cyclic orthoesters, presumably through the capture of a transient oxonium ylide.

Elucidating the mechanism and reactivity of the reaction between the donor–acceptor–acceptor 1,3-bisdiazo compound and cinnamyl alcohol catalyzed by Rh2(OAc)4: a DFT study

“…In view of these issues, to elucidate the mechanism details and the reactivity of two diazo sites, a comprehensive density functional theory (DFT) 34–37 investigation was performed for the D/A/A 1,3-bisdiazo compound ( 1a ) and its reaction with cinnamyl alcohol ( 2a ) catalyzed by Rh 2 (OAc) 4 based on the reported experimental data (Scheme 2). 33 Here, we hope this computational study can give more detailed insights into bi-diazo compounds and support some useful suggestions for the design of diazo compounds.…”

“…With the substrate 2a reacting with intermediate 2-int2 , different chiral compounds would be obtained, which was not observed in the experiment; while when only reacting with 2-int3 , outcome 4 was produced. 33 So, it was necessary to change the chirality of the carbene center. In the transition state 2-TS3 , the lengths of the formed and broken C–Rh bonds were 2.79 Å and 2.69 Å, respectively.…”

“…The frequency calculations also provided the thermochemical corrections at the corresponding experimental temperatures for reactions 1, 2, and 3 (25, 25, and 55 °C, respectively) as well as at a pressure of 1 atm. 33 Meanwhile, to verify the key transition states connected with the corresponding reactants and products, the intrinsic reaction coordinate (IRC) 44,45 calculations were carried out. Moreover, the solvent effect on the reactions in CHCl 3 ( ε = 4.71) was taken into consideration by using the SMD solvation model.…”

“…Recently, Abrams et al reported a donor–acceptor–acceptor 1,3-bisdiazo compound ( 1a ) that included two diazo groups with different substituents, described as D/A (donor/acceptor = phenyl/–CO) and A/A (acceptor/acceptor = –CO/–CO 2 CH 3 ) sites, and investigated their reactivity, as displayed in Scheme 2. 33 This work made the diazo compound family richer. As shown in Scheme 2 for reaction 1, the substrate 1a reacted with cinnamyl alcohol ( 2a ) catalyzed by Rh 2 (OAc) 4 ( Rh-cata ) to generate the product 3 .…”

“…After that, the outcome 4 from reaction 2 could convert to the product 5 at a temperature of 55 °C without Rh-cata (reaction 3). 33 For this unusual bisdiazo compound, a careful theoretical study is necessary to address the following key aspects: (1) to provide details of the mechanistic pathways for the three reactions; (2) to consider the possibility or not of obtaining the expectant product 3 ; (3) to investigate the effect of the reaction environment on the reactions, such as solvent and catalyst; and more importantly, (4) to assess the reactivity difference between the two D/A and A/A diazo sites. In view of these issues, to elucidate the mechanism details and the reactivity of two diazo sites, a comprehensive density functional theory (DFT) 34–37 investigation was performed for the D/A/A 1,3-bisdiazo compound ( 1a ) and its reaction with cinnamyl alcohol ( 2a ) catalyzed by Rh 2 (OAc) 4 based on the reported experimental data (Scheme 2).…”