Gold vs Light: Chemodivergent Reactivity of Diazoesters toward 2H-Azirine-2-carboxylic Acids

Abstract

An orthogonal reactivity of diazo compounds toward azirine-2-carboxylic acids, switching with the reaction conditions, is demonstrated. A gold-catalyzed reaction is Nselective and produces 1,3-oxazin-6-ones, whereas a blue light activation leads to O−H insertion products, azirine-2-carboxylic esters. The observed chemodivergence is explained by the metalbound and metal-free carbenes exhibiting different electronic properties in these reactions. In addition, a high antibacterial potential of the 1,3-oxazin-6-ones synthesized is shown.

2H‐Azirines: Recent Progress in Synthesis and Applications

“…Rostovskii and co‐workers [105] had actually discovered two completely distinct catalytic systems towards the reaction of azirine‐2‐carboxylic acids with diazoesters, resulting in switchable fabrication of 1,3‐oxazin‐6‐ones and azirine‐2‐carboxylic esters (Scheme 66). That is, the oxazinones are formed under gold catalysis via the initial formation of gold carbenes, which is attacked by the azirine nitrogen rather than oxygen atom from carboxylic acid, whereas the O−H insertion products are exclusively formed with the azirine cycle being intact toward the photogenerated carbene under blue light irradiation.…”

Visible photons as ideal reagents for the activation of coloured organic compounds

“…Notably, in the presence of an Au( i ) catalyst, the nitrogen atom in the azirine ring was the exclusive reacting site and a 1,3-oxazin-6-one ring was formed. 291…”

Visible light-mediated photolysis of organic molecules: the case study of diazo compounds

“…Nevertheless, the advancement of the chemistry of free carbenes generated by visible light (or low-energy UV light) can be considered very important because: (i) it is a viable alternative for metal carbenes when the metal catalyst are poisoned by one of the reacting partners; 100 (ii) free carbenes might display a different reactivity of the metal-carbene, leading to a different final product; 63,85,101 (iii) the comparison between reactions performed by metal-carbenes versus free carbenes can provide insightful information on the function of the metal catalyst, thus serving also as a simple tool for mechanistic enquiry; 85,102 (iv) free carbenes can potentially find applications where metal carbenes show limitations, such as in the fields of chemical biology 103 and materials science; 104 and v) the use of free carbenes can be a more cost-effective alternative for the synthesis of racemic or achiral target-molecules, thus avoiding the use of more expensive metal catalysts. 11…”