Radical mechanism of nucleophilic substitution on halocyclohexane systems

Abstract

Chlorocyclohexane does not react in the dark with diphenylphosphide ions in liquid ammonia, but it reacts under irradiation to give the substitution product. Bromocyclohexane reacts slowly in the dark, but this reaction is strongly accelerated by light, and inhibited by p-dinitrobenzene. 3-Bromo-2-tetrahydropyranyl ally1 ether (used as a radical probe) reacts with diphenylphosphide ions under irradiation to give both the straightforward and the cyclized substitution products. This photostimulated reaction is also inhibited by p-dinitrobenzene. It is suggested that the chloro-and bromocyclohexanes and related compounds react under irradiation by the S R N~ mechanism of nucleophilic Substitution.

Nucleophilic Substitution Reactions by Electron Transfer

“…Similar experimental evidence was obtained in the reaction of secondary halides (6-halo-1-heptenes) with Me 3 Sn - 64a,b and R 3 Ge - (R = Me or Ph) 64c ions and in the reaction of cyclohexyl-type bromides, substituted by a cyclizable radical probe, with Ph 2 P - ions . In the photoinitiated reaction of Ph 2 P - ions with 2-chloro-2-methyl-6-heptene, a tertiary chloride, only the cyclized substitution product was obtained, indicating that ring closure is faster than the coupling of the tertiary radical with Ph 2 P - ions .…”

“…The c -C 6 H 11 Cl reacts with Ph 2 P - ions under irradiation to form 33% of substitution by the S RN 1 mechanism. , A dark reaction accelerated by light was observed with the bromo derivative to give substitution mostly by the latter mechanism (93%) …”

“…148,149 Similar experimental evidence was obtained in the reaction of secondary halides (6-halo-1-heptenes) with Me 3 Sn -64a,b and R 3 Ge -(R ) Me or Ph) 64c ions and in the reaction of cyclohexyl-type bromides, substituted by a cyclizable radical probe, with Ph 2 Pions. 150 In the photoinitiated reaction of Ph 2 Pions with 2-chloro-2-methyl-6-heptene, a tertiary chloride, only the cyclized substitution product was obtained, indicating that ring closure is faster than the coupling of the tertiary radical with Ph 2 Pions. 151 In the reaction of the probe 6-bromo-1-hexene with the anthracene radical anion, the ratio of cyclized to uncyclized products was found to decrease with the concentration of the anthracene radical anion as a result of the competition between cyclization of the hexenyl radical and its coupling with the anthracene radical anion.…”

“…18a The c-C 6 H 11 Cl reacts with Ph 2 Pions under irradiation to form 33% of substitution by the S RN 1 mechanism. 150,384 A dark reaction accelerated by light was observed with the bromo derivative to give substitution mostly by the latter mechanism (93%). 384 Related compounds such as cis-and trans-4-tertbutylcyclohexyl bromide 64e and trans-and cis-2-, -3-, and -4-methylcyclohexyl bromides 64c were found to undergo substitution by MSnMe 3 (M ) Li, Na, or K) in a non-stereospecific manner.…”

Radical Cyclization of Haloacetals: The Ueno-Stork Reaction

“…Photoelectron transfer using the diphenylphosphide anion has been reported but has no synthetic value. 119,120 On the other hand, Cossy reported that irradiation of haloacetal in acetonitrile in the presence of triethylamine affords the cyclized products in excellent yields (Scheme 33). 121…”