Formation of a dipolar adduct in the reaction of arylchlorocarbenes with diethyl maleate

Concurrent Cyclopropanation by Carbenes and Carbanions

“…The relative reactivity ( k rel ) of ACN versus TME was determined in the standard manner by allowing a 2:1 ACN/TME mixture to compete for an insufficiency of photochemically generated PhCBr in MeCN/THF solution at 25 °C and determining the 3-Br / 2-Br product ratio by (calibrated) capillary GC analysis. The value of k rel was 0.042 ± 0.01, in keeping with the electrophilic selectivity expressed by PhCBr toward all but the most electrophilic alkenes …”

Cyclopropanation of Alkenes with Halodiazirines as Halocarbene Precursors in Continuous Flow

“…[30] Notably, when diazirine 1 a was reacted with dimethyl maleate in the same conditions, only a very low yield of corresponding cyclopropanes was obtained (less than 9 %, with no traces of any trans-diastereoisomer). [31] This result seems in line with the stabilization of the singlet state of these halocarbenes leading to a stereospecific reaction. [32] The parent bromodiazirines 3 a-3 c possessing electrondonating and electron-withdrawing groups on the aryl ring were also investigated in the reaction with styrene (Scheme 4).…”

“…Importantly, when a lower yield was obtained, e. g. in the reaction of 3‐(chloro)‐3‐(4‐chlorophenyl)‐3 H ‐diazirine 1 b with various alkenes leading to 2 bb – 2 be , no by‐products could be identified, e. g. the corresponding azine or dimeric 1,2‐dichloro‐1,2‐diarylethene which were isolated in thermolysis and photolysis conditions [30] . Notably, when diazirine 1 a was reacted with dimethyl maleate in the same conditions, only a very low yield of corresponding cyclopropanes was obtained (less than 9 %, with no traces of any trans ‐diastereoisomer) [31] . This result seems in line with the stabilization of the singlet state of these halocarbenes leading to a stereospecific reaction [32] …”

A convenient route to 3-substituted isothiazoles using nitrile sulfide cycloaddition chemistry

“…On the other hand, examination of the unreacted dipolarophile recovered from the reaction mixture by 1 H NMR spectroscopy showed the presence of DEF (δ =CH 6.4 ppm, cf 6.0 ppm for DEM), consistent with path (b). As DEM is thermally stable at the reaction temperature it is assumed that it results, either (i) from a reversible cycloaddition which allows the more stable trans-alkene to be generated in the reverse step, similar to that proposed 9 to explain DEF formation in the reaction of arylchlorocarbenes with DEM, or…”