Photoinduced synthesis of functionalized oxetanes via diradical-mediated ring contraction

Abstract

A photochemical ring contraction is reported for the synthesis of oxetanes from dihydrofurans and diazo compounds under catalyst-free conditions.

Visible-light-induced [3+2] cycloadditions of donor/donor diazo intermediates with alkenes to achieve (spiro)-pyrazolines and pyrazoles

“…It is also known that diazo compounds can generate oxonium ylide with oxetane and 2,5dihydrofurans via a carbene intermediate. 61,62 To verify this, a carbene-trapping experiment was carried out with THF, and product 55e was obtained via the formation of an oxonium ylide intermediate (Scheme 5F). Aerward, we evaluated the reactivity of 1e and ammonium salts of DBU under standard conditions.…”

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

“…72 Oxygen ylides have been also explored as key intermediates in ring-expansion strategies employing strained oxetanes to produce substituted THFs, 73 while a ring-contraction method was applied to 2,5-dihydrofurans to afford 3-vinyl oxetanes. 74 Several multicomponent reactions involving the use of cyclic ethers as solvent and a variety of nucleophiles have been reported to afford the corresponding more complex formal O-H insertion products, which are also presumably derived from the involvement of a key oxygen ylide intermediate. 61,62,64,[75][76][77][78][79][80][81][82][83][84] C-C insertion reactions could be achieved with 1,3-diketones 85,86 (with a rare successful example of enantioselective catalysis being demonstrated by Hui and co-authors employing a chiral phosphoric acid catalyst 86 ), and enaminones.…”

Photoinduced Synthesis of Functionalized Oxacyclic Spirooxindoles Via Ring Expansion

“…Currently, the employment of diazo indolinones to initiate a series of transformations has received little attention . On account of foregoing research and our ongoing interest in photochemical reactions, we report herein a novel ring-expansion strategy that allows us to prepare oxacyclic spirooxindoles from epoxides with diazo compounds under the irradiation of 465 nm blue light-emitting diode (LED) light. In our proposed strategy, diazo compounds underwent a photoexcitation process to afford a free carbene species, which enabled the formation of oxonium ylide intermediates followed by a Stevens-type [1,2] shift to give oxacyclic spirooxindoles (Scheme d).…”