Specific and Strong Acceleration of Nitrosation by Nitrosyl Sulfonates Using the Bis-Coordinating Lewis Acid TiCl₄ or SnCl₄

Abstract

Nitrosyl triflate is an excellent donor of NO + to C�C and very unreactive benzenoids, in contrast to the much less reactive nitrosyl mesylate. However, both of these reagents are strongly activated by the bis-coordinating Lewis acids TiCl 4 and SnCl 4 and become super reactive NO + donors. Strong catalysis and activation are even observed with the inherently less electrophilic nitrosyl trifluoroacetate. Monocoordinating strong Lewis acids, e.g., MeAlCl 2 , are relatively ineffective.N itrosyl triflate (1), which is readily generated in a CH 2 Cl 2 solution at −20 °C by reaction of triflic anhydride and tetra-n-butylammonium nitrite (1:1 ratio), is a very useful reagent which can convert olefins at −78 °C into cationic 1,2-diazetium ions (2), which can lead to a variety of reaction products. 1−4 For example, cyclooctene (3) is transformed at −78 °C via the 1,2-oxazetium cation 4 into the products 5−8 (Scheme 1). * sı Supporting InformationThe Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.orglett.3c03768.Experimental procedures and characterization data for novel reactions and products including copies of 1 H and 13 C NMR spectral data for representative compounds (PDF)