A simple, biogenetically modeled synthesis of 4-(methylthio)butyl thiocyanate: the reaction of thiocyanate anion with S-methyl-(1,n)-epithionium ions

Abstract

. J. Chem. 64, 940 (1986).The reaction of S-methylthiolanium fluorosulphate with thiocyanate ion gives predominantly 4-(methy1thio)butyl thiocyanate, a result which is in accord with a hypothesis for the biogenesis of this compound, and which has implications for the natural occurrence of analogous thiocyanates.M. H. BENN et VINOD K. SINGH. Can. J. Chem. 64, 940 (1986).La rkaction du fluorosulfate du S-mt5thylthiolanium avec l'ion thiocyanate conduit principalement au thiocyanate de (mt5thyl-thio)-4 butyle; ce rt5sultat est en accord avec une hypothbse relative h la biogknbse de ce compost5 et il a des implications relativement h l'existence h 1'Ctat nature1 de thiocyanates analogues.[Traduit par la revue] Introduction Glucosinolates are naturally occurring anions, characterized by the general structure 1. They are commonly, but not exclusively, encountered within plants of families that constitute the Capparales and their decomposition is a matter of considerable current interest, because the products are known to be important factors in determining the palatability and toxicity of these plants to man and other animals (see ref. 1, and references therein).Of the nearly 100 glucosinolates that have been isolated, or inferred to exist, all can be catabolized to isothiocyanates or nitriles. These products are known to arise from the-aglucones that are released from 1 by myrosinase (thioglucoside glucohydrolase EC 3:2:3:1) (Scheme 1) (1). In contrast with this generality, only three, the allyl (2), benzyl (2, 3), and 4-(methylthio)butyl(4) compounds are known to be capable of yielding the corresponding thiocyanates, and they do so under conditions that indicate that these conversions involve other, plant-specific, enzymes.To account for this striking restriction it has been postulated (5) that the thiocyanates are formed from aglucones by a fragmentation process in which departure of sulphate, instead of being concerted with the [1,2]-shift of the substituent R that yields the isothiocyanates, results in fragmentation to thiocyanate anion and a cation corresponding to R. Recombination of this ion pair would then be expected to preferentially form the thiocyanate as a consequence of the high nucleophilicity of the S-terminus of the ambident thiocyanate anion. Also plausible is the possibility that the fragmentation process is a consequence of a Z-, E isomerization that destroys the geometry required for the concerted isothiocyanate-forming reaction (Scheme 2) (5). (The aglucone intermediates are shown in Schemes 1 and 2 in their free, protonated, forms. It may well be that they are bound, through bivalent sulphur, to a metal ion: this would inhibit tautomerism and interconversion of E and Z isomeric forms.)Fragmentation should be favoured for substrates that yield relatively stable cations. The allyl and benzyl systems are textbook examples of such ions, and we visualized 4-(methylthio)butyl glucosinolate (2) (n = 4) as yielding the even more stable S-methylthiolanium cation. In this latter case there is then a requ...

Deciphering the Differences in Ambident Reactivity between the Cyanate, Thiocyanate Ions, and their P‐ and As‐Containing Analogues

“…According to experiments using the [SCN] À anion, both isomers have been accessed with carbon-electrophiles, but the thiocyanate (RÀ SCN) isomer is typically favoured kinetically, as implied by the positive ΔΔG � values. [24,[102][103][104] Furthermore, the reaction of [NCSe] À ion with i PrÀ Br results exclusively in the selenocyanate (MeÀ SeCN) isomer, [105] in line with the calculated positive ΔΔG � selectivity value.…”

Behaviour of iprit carbonate analogues in solventless reactions

“…This result can be ascribed to the formation of the 1-methylthietanium, a 4memebered cyclic intermediate, which is known to be less stable than the 3-or 5-memebered intermediates. 21 On the other hand, 4-(methylthio)butyl methyl carbonate 5 showed to react readily with the nucleophile forming the alkylated product 26 in good yield (66%).…”

Chemical Behavior and Reaction Kinetics of Sulfur and Nitrogen Half-Mustard and Iprit Carbonate Analogues

“…d GC-MS analysis showed also 35% of monomethylated product and several unidentified products. Results collected (entries 1−3, Table 1) seem to suggest that the 1-methylthietanium, only scarcely reported in the literature, 46 is a less stable intermediate compared to 1,1-dimethylazetidinium. 47 Most probably the anchimeric effect of the sulfur mustard carbonate 2 is not strong enough to stabilize the strained four-member cyclic intermediate.…”