Sulfimidation of thioether groups—a versatile method for modifying and linking thia/oxa crowns

Abstract

Reaction of the mixed thioether/ether crowns [9]aneO₂S 1, [12]aneO₃S 2 and [18]aneO₄S₂3 with one mol. equivalent of the aminating agent MSH (o-mesitylsulfonylhydroxylamine) in Et₂O results in the formation of the mono-sulfimidated systems {[9]aneO₂(SNH₂)}⁺1a, {[12]aneO₃(SNH₂)}⁺2a and {[18]aneO₄S(SNH₂)}⁺3a, while using two mol. equivalents of MSH with 3 gives the disulfimidium cation {[18]aneO₄(SNH₂)₂}²⁺3b. All of these species have been isolated in good yields as the [mesSO₃]⁻ (mes = 2,4,6-Me₃C₆H₂) salts and can be readily converted to the [BPh₄]⁻ salts by metathesis with Na[BPh₄]. Treatment of 1a or 2a with lithium diisopropylamide (LDA) and N-bromosuccinimide (NBS) at −78 °C, followed by addition of a further equivalent of the parent thia/oxa crown, gives monocationic N-bridged sulfimide bicyclic compounds (4 and 5 respectively), in which the crowns are linked by the sulfimidic nitrogen. Reaction of 3a with LDA and NBS leads to formation of the {([18]aneO₄S₂)N}⁺ cation 6 which exhibits an intramolecular S–N–S bridge. Crystallographic studies on representative examples of each compound type are described, together with their spectroscopic properties.