Trapping reactions of sulfenes generated from sulfonic acid derivatives and bases, 2. [4 + 2] cycloadditions of 1,2,3,4,5‐pentamethylcyclopentadiene and 1,3‐diphenylbenzo[c]furan with sulfenes

Abstract

Sulfenes 2a-0, generated in situ from sulfonyl chlorides and Et3N, are trapped by 1,2,3,4,5-pentamethylcyclopentadiene Sulfenes generated in situ from sulfonyl chlorides and triethylamine (Et3N) react with cyclopentadiene according to a [4 + 21 cycloaddition only if they bear either bulky or electron-attracting groups [']. We now found that 1,2,3,4,5-pentamethylcyclopentadiene (6) is a diene suitable for trapping simple sulfenes. It is easily does not dimerize, undergoes Diels-Alder reactions with dienophiles 100 times more rapidly than ~yclopentadiener~], and -due to its relatively low acidity (pKs = 26.1 as opposed to 18 for cycl~pentadiene [~]) -also allows the use of bases stronger than Et3N without giving rise to sulfonylations['l. Although 6 is slightly less reactive than strongly polar enamines such as N-(2-methyl-1 -propenyl)pyrrolidine, as a hydrocarbon it requires sulfene 2 itself and not sulfeneadducts like 3, 4, or Reaction of 1,2,3,4,5-Pentamethylcyclopentadiene (6) with Methanesulfonic Acid Derivatives l a and Bases B (Scheme 1 and Table 1) In tetrahydrofuran (THF), 6 readily traps the sulfene generated in situ from mesyl chloride or methanesulfonic acid anhydride/Et3N to afford [4 + 21 cycloadduct 8a (72 and 60%, respectively). In acetonitrile (MeCN) mesylsulfene (7) is formed additionally which surprisingly not only undergoes a [4 + 21 cycloaddition affording endolexo-9 (crystal structure analyses) but also, to a slight extent, a [2 + 21 cycloaddition furnishing 10 the configuration of which was as cycloaddition partners. also proven by a crystal structure analysis. This is the only example of a competing [2 + 21 cycloaddition.Mesyl chloride and Et3N were allowed to react completely at -40°C in MeCN to yield the mesylsulfene-Et3N-S,N adduct 5L61. 6 was subsequently added and only the cycloadducts 9 and 10 derived from mesylsulfene were obtained. When, however, in in-situ experiments, Et3N was replaced by the "proton sponge" (PS) N;N, ","-tetramethyl-1 ,s-naphthalenediamine which for sterical reasons cannot form amine adducts with sulfened51, only the sulfene cycloadduct 8a (66 and 6O%, respectively) was formed, even in MeCN. This proves that the sulfene-Et3N-S,N adduct 4, which cannot be directly detected, represents a precursor of the mesylsulfene-Et,N-S,N adduct 5, and that the sulfene itself undergoes a [4 + 21 cycloaddition affording 8a. This is even more clearly evident from the formation of 8a (48") from 6 and mesyl chloride in the presence of NaH as a base in THE The application of this novel method to the generation of amine-free sulfenes with the formation of hydrogen and poorly-soluble sodium halide prevents secondary reactions of sulfenes which proceed via 3 and 4.Furthermore, with mesyl fluoride, this method even affords 12% of 8a. On the other hand, the use of Et3N in boiling MeCN or THF was here unsuccessful. When an equimolar mixture of 6 and N-(2-methyl-l-propenyl)pyrrolidine was allowed to react with mesyl chloride/Et3N at 0°C in THF, the sulfene was trapped exclusively by the en...

Halogen migration vs. hydrogen halogenide elimination in reactions of 1-chloro-2,2,2-trifluoroethansulfonyl chloride and 1,2,2,2-tetrafluoroethansulfonyl fluoride with amines: theoretical and experimental investigation

“…This is not contrary to the experimental data evidencing sulfenes as highly unstable species. They easily undergo further transformations, for example, as substrates in the Diels-Alder reactions [12,13] or in the reaction with amines [9,14,15]. Structures and relative stabilities for series of sulfene adducts with amines were analyzed recently in the theoretical paper of Bucher [16].…”

Selectivity in the C–H Activation Reaction of CH3OSO2CH3 with [1,2,4-(Me3C)3C5H2]2CeH or [1,2,4-(Me3C)3C5H2][1,2-(Me3C)2-4-(Me2CCH2)C5H2]Ce: To Choose or Not To Choose

“…Hydrolysis (H 2 O) and analysis by GCMS when only resonances due to C and D are present in the 1 H NMR spectrum show the presence of I and II at m / z 312 and 326 amu, respectively, along with Cp′H. The [2 + 4] cycloaddition of sulfene with cyclopentadiene or a substituted cyclopentadiene is one of their characteristic reactions, which suggests that, if sulfene is formed, trapping by Cp′H and Cp″H will yield I and II . The cycloadduct between sulfene and C 5 HMe 5 is an isolated compound, suggesting the use of C 5 HMe 5 as a trap in the reaction shown in eq .…”