Low-valent carbon species-involved chemical reactions have been one of the important cornerstones in morden synthetic strategy . Up to now, much significant progress on transition metal-and photo-catalyzed cross-coupling between carbenoids and C-H, N-H, C-C, C=C, C≡C, and C-heteroatom bonds has been achieved . By contrast, monovalent carbyne-based transformations have been rarely explored, mainly due to that carbyne species are not readily available . In 1967, Strausz first reported that Hg{C(=N 2 )CO 2 Et} 2 could produce free carbyne radicals [:C(•)-R] under UV-Vis irradiation, this carbyne species feature with dual radical and carbene behaviour, such as Csp 3 -H carbenoid insertion and carbene-alkene [1 + 2] cycloaddition (Fig. ) . Since then, the exploration of alternative carbyne precursors has always kept going forward by chemists. In 2018, Gaunt and Seuro innonatively confirmed that -diazo iodonium triflates could act as an another carbyne precursor to form diazomethyl radical [N 2 =C(•)-R] by visible-light-mediated metal-photocatalysis, this -diazo onium salts would react with arenes and methionine residues, allowing for aryl Csp 2 -H bond and protein diazomethylation, respectively (Fig. -II) . Subsequently, Seuro further found -diazo iodonium salts could still cleavage C(sp 2 )-C(sp 2 ) double bonds by transition metal-catalysis, followed by inserting a monovalent carbon unit into alkenes (Fig. -III) . Interestingly, Wang also developed a cross-coupling of alkynes with -diazo sulfonium triflates to produce 1,4-dicarbonyl alkenes, in which free carbyne radicals instead of diazomethyl radicals were involved in a radical cyclization to alkynes under visible-light-promoted metal-free photocatalysis . Considering these significant discoveries which mean that -diazo onium salts can generate carbyne species by utilizing different catalysis systems, we questioned whether diazomethyl radical [N 2 =C(•)-R] could be chemoselectively trapped by alkenes to form alkyl radicals under photocatalysis system.