Dichloromethane as solvent and reagent: a case study of photoinduced reactions in mixed phosphonium‐iodonium ylide

Abstract

Several years ago the photoinduced reaction of mixed phosphonium-iodonium ylides (1) with acetylenes (2) to give λ 5 -phosphinolines (3) and substituted furans (4) was described. This reaction is one-pot, metal-free synthesis of heterocycles 3 and 4 with the yields of 40% to 80%. The reaction proceeds only in dichloromethane (DCM) at the high ylide concentrations (>0.01 mol/L). The product analysis by 31 P NMR, electrospray ionization mass spectrometry, UVvis spectrophotometry, and the dynamic light scattering study of the self-aggregation of the ylide in DCM showed a dual role of the solvent in the photoinduced reactions of mixed phosphonium-iodonium ylide: (i) at the low ylide concentrations (<0.01 mol/L), the conjugated photoinitiation of the chain reaction in DCM results in the formation of chlorine-containing products and (ii) at the high ylide concentrations (>0.01 mol/L), the photolysis mechanism is determined by self-organization of the ylide molecules to give large stable aggregates in DCM, in which the target heterocycles are synthesized. Two important issues follow from the study. First, the annulation reaction between mixed phosphonium-iodonium ylide and acetylenes occurs only when the reactive intermediates are in close proximity to one other, and, second, DCM is not inert reagent in reactions occurring with participation of radicals and in one form or another can participate in photoinduced radical reactions of various solutes.KEYWORDS annulation with acetylenes, dichloromethane, phosphonium-iodonium ylides, radical reactions, selfassembly This article is dedicated with respect and affection to the memory of the late Prof. Nikolay S. Zefirov.

The Photophysics of Dibenzo[a,j]phenazine

“…The reaction is indicated by a decrease of the DBPHZ absorption bands as well as the emergence of a band peaking at 466 nm. Reactions of dichloromethane with solutes in the presence of UV‐light have been described before [42,43] . Tracing the absorption changes with time (or photon equivalents, cf.…”

“…Reactions of dichloromethane with solutes in the presence of UV-light have been described before. [42,43] Tracing the absorption changes with time (or photon equivalents, cf. Figure 2, insert) reveals rather complex reaction kinetics.…”

CIDNP as a tool to unveil the reaction mechanism: interaction of mixed phosphonium–iodonium ylide withp-methoxyphenylacetylene

“…If the critical concentration dependence for the reaction with acetylenes is accounted for by the specific microheterogeneoos structure of the ylide solutions in DCM, 6 the unusual features of the reaction, such as induction time, acid catalysis and presence of radicals, are inconsistent with the primarily suggested mechanism of product formation. 7 This mechanism involves heterolytic scission of the C–I + Ph bond with elimination of PhI under irradiation and formation of λ 5 -phosphinoline 3 and furan derivative 4 from an intermediate carbocation (or a carbene) in parallel reactions.…”

“…Reaction of ylide 1 with acetylenes 2 is characterized by remarkable features: (i) it proceeds only in dichloromethane (DCM) (ii) at high ylide concentrations (>0.01 M) (iii) with induction time, 3 (iv) is catalyzed by acids 4 and (v) relatively stable free radicals are observed by EPR in the reaction mixture. 5 If the critical concentration dependence for the reaction with acetylenes is accounted for by the specic microheterogeneoos structure of the ylide solutions in DCM, 6 the unusual features of the reaction, such as induction time, acid catalysis and presence of radicals, are inconsistent with the primarily suggested mechanism of product formation. 7 This mechanism involves heterolytic scission of the C-I + Ph bond with elimination of PhI under irradiation and formation of l 5 -phosphinoline 3 and furan derivative 4 from an intermediate carbocation (or a carbene) in parallel reactions.…”

Advances in Reactions of Iodonium Ylides

“…膦-碘叶立德与乙炔的反应开辟了一条取代呋喃类 化合物的合成途径. Matveeva 等 [50] 图式 31 混合的膦-碘叶立德与乙炔合成取代呋喃和环状膦啉 Scheme 31 Synthesis of substituted furans and annelated phosphinolines from mixed phosphine-iodonium ylide and acetylene 随后的几年里, Nekipelovaa 等一直致力于研究混合 的磷-碘叶立德与乙炔化合物的光环化反应, 相继发表 了酸对该反应体系的催化作用 [51][52] 、涉及自由基的反应 机理 [53][54] 以及溶剂二氯甲烷对反应的影响 [55] 等方面的 文章.…”