10.1002/chem.202101788
Chemistry - A European Journal
COMMUNICATION
O
H
N
highlights the role that diazophosphonates can play as
surrogates for less stable diazoalkanes.
OEt
OEt
P
1. PhMe, reflux
( )n
N
( )n
N2
2. MeOH, aq. NaOH
SiMe3
SiMe3
12a n = 1
12b n = 2
12c n = 3
13a n = 1 (73%)
13b n = 2 (85%)
13c n = 3 (15%)
Experimental Section
For full details of all experimental procedures and copies of 1H and
13C NMR spectra, see the Supporting Information.
N2
H
N
N
OEt
P
1. PhMe, reflux
OEt
O
2. MeOH, aq. NaOH
Acknowledgements
H
14
15 (83%)
We thank the BBSRC Doctoral Training Programme (grant ref
BB/M008770/1), the EPSRC Centre for Doctoral Training in
Sustainable Chemistry (grant ref EP/L015633/1) and the
University of Nottingham for studentships (to F.R.S., M.T.G.
and S.M.N. respectively).
N2
H
N
N
OEt
OEt
P
1. PhMe, reflux
O
2. MeOH, aq. NaOH
CO2Me
CO2Me
16
plus
Keywords: pyrazole • diazophosphonate • dipolar
17 (85%)
N-[PO(OEt)2]-17
cycloaddition • 1,5-sigmatropic rearrangement
Scheme 6. Intramolecular cycloaddition of diazophosphonates to alkynes
to give cycloalkapyrazoles.
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Thus
the
alkynoic
acid
Me3SiC≡C(CH2)4CO2H was treated with methanolic
potassium carbonate to give the desilylated material,
heptynoic acid in near quantitative yield. Conversion into the
diazophosphonate 14 proceeded without incident by way of
the corresponding hydrazone (see Supporting Information).
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intramolecular cycloaddition reaching completion in 1.5 h and
gave tetrahydroindazole 15 in high yield. Finally, we
investigated the effect of introduction of an electron-
withdrawing ester group onto the alkyne dipolarophile in
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rate of reaction. In the event, this proved to be the case.
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by oxidation of the corresponding hydrazone, prepared as
shown in the Supporting Information, gave the expected
diazophosphonate 16 together with the phosphorylated
version of pyrazole 17 (68% combined), the cycloaddition
occurring during attempted isolation and purification of the
diazophosphonate 16 due to the reactive nature of the
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diazophosphonate 16 and the phosphorylpyrazole to the
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aqueous work-up (Scheme 6).
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cycloaddition reactions of the diazophosphonates again
emphasize the beneficial influence of the phosphoryl group
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5
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