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

A versatile photochemical ring-expansion protocol for the synthesis of oxacyclic spirooxindoles under catalyst-free conditions is described. The reaction is enabled by the use of unstrained O-containing heterocycles with 3-diazoindolin-2-ones under visible-light irradiation. Several synthetic advantages for this method are exhibited, including mild conditions, good functional group tolerance, operational simplicity, and scalability. Mechanistic studies indicate that the transformation may proceed through the formation of oxonium ylide intermediate followed by an ionic cyclization.O xacycles are abundant in plenty of biologically active nature products and molecular drugs. 1,2 Among these compounds, spirooxindole-fused oxacycles play an important role in synthetic and pharmaceutical chemistry as key structural moieties, such as XNE907, CB2 receptor antagonist, Aspergilline A, and Tryptoquivaline T (Figure 1). 3 Compared Scheme 1. Previous Literature and Reaction Design Letter pubs.acs.org/OrgLett

A visible-light-induced trifluoromethylsulfonylation reaction of diazo compounds is herein reported. This developed synthetic method captures the relatively rare trifluoromethyl sulfone radicals via coordination to the Mn(acac) 3 catalyst, delivering the corresponding α-trifluoromethyl sulfone esters in good to moderate yields (up to 82%). This protocol exhibits broad substrate scope and is easily carried out under mild reaction conditions. Furthermore, a plausible mechanism of the reaction was investigated through DFT calculations.

A visible light-induced O−H insertion reaction of diazo compounds is herein reported. This developed synthetic method, which is different from traditional pathways that rely on transition metals, Lewis acids or Brønsted acids, does not use any catalyst and produces valuable α-hydroxy and α-alkoxy esters in good yields (up to 98%). This protocol exhibits a broad substrate scope and good functional group tolerance. Notably, a gram-scale synthesis in continuous photo flow fashion has been performed.

A visible light-induced synthesis of polysubstituted oxazoles from diazo compounds is herein reported. This developed synthetic method differs from traditional routes that rely on transition metals and external chemical oxidants....