Dichloromethane as solvent and reagent: a case study of photoinduced reactions in mixed phosphonium‐iodonium ylideстатья
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Дата последнего поиска статьи во внешних источниках: 10 августа 2018 г.
Аннотация:Several years ago the photoinduced reaction of mixed phosphonium‐iodonium
ylides (1) with acetylenes (2) to give λ5‐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 31P 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.