The products of reaction of N-substituted amidines 5 with
hypervalent iodine reagents such as (diacetoxyiodo)benzene (DAIB),
bis(trifluoroacetoxy)iodobenzene (BFIB) and
[methoxy(tosyloxy)iodo]benzene (MTIB) are determined by the reagent, the
amidine substituents and the reaction temperature.
C-Alkyl-N-arylamidines 5a–d cyclise in high
yield giving benzimidazoles 6 but C,N-dialkyl- and
C,N-diaryl-amidines 5e–l rearrange to give
products derived from an intermediate carbodiimide. Use of
N2-phenylfuran-2-carboximidamide 5j leads to
N-(2-furyl)acetamide 15 in good yield, illustrating a
convenient route to stable derivatives of highly unstable 2-aminofuran.
The rearrangement of C,N-diarylamidines on reaction
with DAIB contrasts with the observed formation of benzimidazole when
the same precursors are treated with lead tetraacetate (LTA). Evidence
is presented to support the view that the mode of reaction is determined
by the nature of the leaving group in an imide intermediate 19: very
good leaving groups [e.g. PhI, N2, AgCl and
PhSO2O- (aq.)] appear to favour
rearrangement whereas poorer leaving groups [e.g.
Cl-, Me2S, Me3N and
PhSO2O- (non-aq.)] favour
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Journal of the Chemical Society, Perkin Transactions 1
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