Nitryl iodide addition reactions

The regioselective addition of nitryl iodide to alkenes, followed by base-induced elimination, gives nitroalkenes. Nitryl iodide is generally prepared by the reaction of AgN02 and iodine. 

Treatment of an epoxide, namely methyl 2,3-anhydro-4,6-0-benzylidene-oi-D-allopyranoside (78, Scheme 21), with nitryl iodide using methanol as the solvent has been reported.123 Rather than the expected nitration, opening of the epoxide occurred to afford 30% of methyl 4,6-0-benzylidene-3-0-methyl-oi-D-glucopyranoside (79), 10% of methyl 4,6-0-benzylidene-2-0-methyl-a-D-altropyranoside (80), and a water-soluble material. The water-soluble material was later determined to be a mixture of the 2-0- (81) and 3-0-methyl (82) products, with the benzylidene acetal removed, a result consistent with a later study.124 Performing the reaction in the absence of the silver salt resulted solely in formation of the water-soluble product. The preponderance of the diequatorial product 81 is in violation of the Flirst-Plattner rule, which predicts more of the diaxial product. The authors explanation for the anti-Fiirst-Plattner addition is as follows. 

The use of iodine-containing pseudohalogens has been demonstrated to cause a variety of side reactions. Treatment of methyl 5-0-benzoyl-2,3-dideoxy-3-D-g/ycero-pent-2-enofuranoside (83, Scheme 22) with nitryl iodide afforded none of the desired addition product, but gave a quantitative yield of furfuryl benzoate (86). The same result was obtained by treating 83 with iodine nitrate, or with iodine alone.125 The rationale for this undesired result lies in the ability of iodine to act as a Lewis acid, polarizing the glycosidic bond, generating an oxacarbenium cation, which then decomposes to the stable aromatic 86. 

Differing from the reaction with dinitrogen tetroxide/iodine (see following section), the addition of nitryl iodide to ( )-l,2-diphenylethylene gave a mixture of diastereomers, as determined by H-NMR spectroscopy129. 

This is surprising, since the reaction of dinitrogen tetroxide with (E)-, 2-diphenylethylene in diethyl ether produced a 3 2 mixture of diastereomeric l,2-dinitro-l,2-diphenylethanes134 The reaction of 2-cholestene with dinitrogen tetroxide/iodine afforded 2/ -iodo-3a-nitro-5oi-chole-stane, this was also the product obtained by the addition of nitryl iodide (see previous section). 

Addition of olefins. The work of Hassner et al. (1, 757) on addition of nitryl iodide to olefins has now been published.1 The reaction probably proceeds by a free-radical addition involving N02-. 

The NO2 radicals obtained from nitrite ions in acidic solution add to olefins regioselectively. The resulting radical is oxidized in situ by CAN to provide nitroolefins, even labile ones, in high yield and short reaction times.32 The second reaction in Fig. 5 shows another preparation by the addition of nitryl iodide, from potassium nitrite and iodine, followed by a base-induced elimination of hydrogen iodide. A radical mechanism is probably not involved. This mild one-pot method, a valuable alternative to other published techniques, is accomplished in a non-aqueous medium and gives good yields and regioselectivities even with sterically hindered substrates. 

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