Nitrosyl Triflate and Nitrous Anhydride, Same Mode of Generation, but Very Different Reaction Pathways. Direct Synthesis of 1,2-Oxazetes, Nitroso or Bisoxazo Compounds from Olefins

Abstract

Nitrosyl triflate (TfONO) can be generated in situ from tetra-n-butylammonium nitrite and triflic anhydride (1:1) in CH2Cl2 solution at ca. −30 °C. It acts as a powerful and soluble nitrosating agent with a wide range of olefinic or aromatic substrates. Nitrous anhydride (ON–O–NO) can be generated in the same way using tetra-n-butylammonium nitrite and triflic anhydride (2:1) in CH2Cl2 solution at ca. −30 °C. Each reagent has been isolated and characterized. They react with olefins to give different products. Nitrosyl triflate is an excellent reagent for generating either vinylic or allylic nitroso compounds or their dimeric bisoxazo derivates. Nitrous anhydride efficiently converts many olefins to 1,2-oxazetes in a single step, making this class of compounds readily available from olefins for the first time. We have also discovered another route to 1,2-oxazetes involving a novel rearrangement/isomerization of allylic nitroso compounds which is catalyzed by Pd–C/H2.

Mechanism of the Reaction of Olefins with Nitrous Anhydride (O═N–O–N═O) to Form 1,2-Oxazetes

“…In our initial paper on the formation of 1,2-oxazetes from olefins, we reported that the reaction of prenyl benzoate with nitrous anhydride led to 1,2-oxazete formation based on liquid chromatography mass spectral data, which showed a peak corresponding to the 1,2-oxazete product. While small amounts of 1,2-oxazete may have been formed in our initial experiments, the major products were hydroxy oxime 28 and α-hydroxy ketone 29 .…”

“…We recently reported that the reaction of tetra- n -butylammonium nitrite with triflic anhydride in CH 2 Cl 2 at −20 to −30 °C can be used to generate either nitrosyl triflate (CF 3 SO 2 ONO) or nitrous anhydride (ON–O–NO) using a 1:1 or 2:1 ratio of the two reactants, respectively . Nitrosyl triflate and nitrous anhydride react with olefinic substrates by very different pathways, as exemplified by cedrene ( 1 ) as the substrate that forms allylic nitroso compound 2 with nitrosyl triflate (−30 °C) or 1,2-oxazete 3 with nitrous anhydride (−30 °C), as summarized in Scheme .…”

“…W e recently reported that the reaction of tetra-nbutylammonium nitrite with triflic anhydride in CH 2 Cl 2 at −20 to −30 °C can be used to generate either nitrosyl triflate (CF 3 SO 2 ONO) or nitrous anhydride (ON− O−NO) using a 1:1 or 2:1 ratio of the two reactants, respectively. 1 Nitrosyl triflate and nitrous anhydride react with olefinic substrates by very different pathways, as exemplified by cedrene (1) as the substrate that forms allylic nitroso compound 2 with nitrosyl triflate (−30 °C) or 1,2-oxazete 3 with nitrous anhydride (−30 °C), as summarized in Scheme 1. The conversion of olefins to 1,2-oxazetes is especially noteworthy because (1) it is a fundamentally new addition pathway to C�C, (2) very few 1,2-oxazetes had previously been reported, 2 and (3) it involves a novel reaction pathway, possibly involving free radical intermediates.…”

“…1 Nitrosyl triflate and nitrous anhydride react with olefinic substrates by very different pathways, as exemplified by cedrene (1) as the substrate that forms allylic nitroso compound 2 with nitrosyl triflate (−30 °C) or 1,2-oxazete 3 with nitrous anhydride (−30 °C), as summarized in Scheme 1. The conversion of olefins to 1,2-oxazetes is especially noteworthy because (1) it is a fundamentally new addition pathway to C�C, (2) very few 1,2-oxazetes had previously been reported, 2 and (3) it involves a novel reaction pathway, possibly involving free radical intermediates. 1 We now report a series of experiments that clarify the mechanism of the reaction of nitrous anhydride with olefins to form 1,2-oxazetes and confirm our initial suggestion that the reaction proceeds via free radical intermediates.…”

“…The conversion of olefins to 1,2-oxazetes is especially noteworthy because (1) it is a fundamentally new addition pathway to C�C, (2) very few 1,2-oxazetes had previously been reported, 2 and (3) it involves a novel reaction pathway, possibly involving free radical intermediates. 1 We now report a series of experiments that clarify the mechanism of the reaction of nitrous anhydride with olefins to form 1,2-oxazetes and confirm our initial suggestion that the reaction proceeds via free radical intermediates.…”