Science of Synthesis

Rück-Braun, K.; Priewisch, B., Science of Synthesis, (2007) 31, 1329.

Since deprotonation of the Wheland intermediate [Ar1+(H)NO] is the rate-determining step in the nitrosation of an arene (Ar1H) (see Section ‌31.22.1.1‌), the usual acid-catalyzed generation of nitrosonium cations is counterproductive. The use of commercially available nitrosonium tetrafluoroborate in acetonitrile offers the possibility of aromatic nitrosation in nonaqueous solution,[‌40‌] in which the reactions are conducted under argon at room temperature or below. Anisole (‌24‌, R1 = R2 = R4 = R5 = H; R3 = OMe) and related methoxylated benzenes containing one or two methyl groups, but unsubstituted para to the ether group, are nitrosated in high yields to give the corresponding nitrosoamines ‌25‌ (‌Scheme 15‌). This occurs without hydrolysis of the ether linkage; a problem commonly observed during nitrosation of similar substrates under aqueous conditions. 15N-Labeled 1-methoxy-4-nitrosobenzene can be prepared by the use of 15N-nitrosonium tetrafluoroborate.[‌41‌] In contrast, the para-substituted compound 4-methoxytoluene (‌24‌, R1 = OMe; R2 = R3 = R5 = H; R4 = Me) is considerably less reactive under the standard conditions, yielding only traces of a nitroso compound. Similarly, brominated anisoles react much less well than anisole and longer reaction times than usual are required in order to obtain the corresponding nitroso compounds; even so, the yields are mediocre.

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References