Nitronium fluoborate

Nitronium fluoborate also reacts with silylallenes, as indicated in Eq. 13.40(38], Attack of the electrophile at the allene carbon atom distal to the silicon atom, 1,2-silicon migration and ring closure lead to a silyloxazole. Exposure of this material to bromine in a second step gives 124 in 72% overall yield from 123. This annula-tion is best performed with tert-butyldimethylsilylallenes. With trimethylsilyl compounds, protodesilylation is a competing side reaction. 

Prepd by reacting ethylenediamine dinirra-mine with nitronium fluoborate in acetonitrile at-30°(Ref 3). No props are given Refs l)Beil, not found 2)ADL, Synthesis HE s, 2nd Report (1951), p 220 3)Aero-jec General Corp, BritP 1126591 (1968) CA 70, 67584 (1969)... 

With dinitrogen pentoxide pyridine gives 1-nitropyridinium nitrate sa and with nitronium fluoborate the corresponding fluoborate is formed Pyridine forms a 1 1 complex with phosphorus pentachloride Sc with sulphur dioxidei29 (43) and with sulphur trioxide o (44). The last is useful as a sulphonating agent (p. 80), and is formed from its components in carbon tetrachloride, from pyridine and fuming sulphuric acid, and from pyridine and chlorosulphonic acid. Its reactions are discussed later (p. 177). 

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