LED lighting as a simple, inexpensive, and sustainable alternative for Wolff rearrangements

Abstract

The Wolff rearrangement suffers from many drawbacks with respect to its practical execution in the laboratory. Herein, commercial LED lamps are employed as a sustainable alternative for the classic protocols typically used for Wolff rearrangements.

Blue light-promoted photolysis of aryldiazoacetates

“…Although this photolysis phenomenon is well known for other diazocompounds using UV-light, 9 , 16 , 18 one can note here that the presence of a donor group at the aryldiazoacetates 1a and 1b (or the removal of an acceptor group, as one can observe the same trend comparing the UV-Vis absorption spectra of 2a and 2b ) is responsible for a significant bathochromic shift in their UV-Vis absorbance spectra, thus allowing the photolysis process to occur in the visible region. 10 , 16 …”

“…In contrast to the numerous protocols reported on thermal processes, photochemical studies with diazocompounds have been performed mostly several decades ago, 9 and modern applications are relatively scarce. 10 , 11 Among these, Suero and co-workers have recently demonstrated that a hypervalent iodine reagent carrying a diazoacetate moiety could be employed in a photoredox-catalyzed protocol for the C–H functionalization of a variety of arenes. 11 b In the sequence, the diazocompounds produced could be further engaged in classical reactions, thus representing an overall formal process to access carbyne equivalents.…”

Blue Light‐Promoted N−H Insertion of Carbazoles, Pyrazoles and 1,2,3‐Triazoles into Aryldiazoacetates

“…When pyrazole 11 a is kept fixed and the aryldiazoacetate component is varied, again good yields are obtained for the corresponding insertion products 12 i – 12 s , which are produced in a range of 47–79% (Scheme , molecules 12 i – 12 s ). In addition, aryldiazoketones, such as 2‐diazo‐1,2‐diphenylethan‐1‐one 7 p or 1‐diazo‐1‐phenylpropan‐2‐one 7 q , can undergo a blue light‐promoted Wolff rearrangement (see the SI for their UV‐Vis absorption spectra), leading to the formation of ketene intermediates, which can be trapped by pyrazole to afford amides 12 t and 12 u , in 88% and 61% yields, respectively (Scheme , molecules 12 t and 12 u ).…”

Adições de aza-Michael em diazocetonas α,β-insaturadas e reações de inserção em ilídeos β-cetosulfoxônios

“…A formação da espécie reativa ceteno no rearranjo de Wolff pode ocorrer de três maneiras 22,23 : termicamente, via catálise metálica e fotoquimicamente. O primeiro método é o menos usual dos três visto que o aquecimento a altas temperaturas (~180 °C) pode levar a formação de produtos indesejáveis diante da sensibilidade do substrato.…”

“…Por último, mas não menos importante, o emprego de luz para a decomposição do grupo diazo é o protocolo mais eficiente dos três, essencialmente pelas condições brandas empregadas. A literatura descreve o uso de lâmpadas de mercúrio, CLC e LED como fontes de fótons nessa reação 23 .…”