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Allenylphosphonates ― Useful Precursors of Pyrazoles and 1,2,3‐Triazoles
Author(s) -
Chakravarty Manab,
Bhuvan Kumar N. N.,
Sajna K. V.,
Kumara Swamy K. C.
Publication year - 2008
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200800490
Subject(s) - diad , chemistry , cycloaddition , stereochemistry , retrosynthetic analysis , reaction conditions , medicinal chemistry , organic chemistry , catalysis , total synthesis , polymer , copolymer
The synthesis of new pyrazoles and triazoles, with or without phosphorus substituents, from allenylphosphonates is described. Thus, Ph 3 P‐promoted reactions of the allenylphosphonates (OCH 2 CMe 2 CH 2 O)P(O)CH=C=CRR′ [R = H, R′ = Me ( 1b ), R = R′ = Me ( 1c )] with DIAD/DEAD lead to phosphonopyrazoles by utilizing the –CO 2 R functionality of DIAD/DEAD for cyclization. The products derived from allenylphosphonates with an α‐phenyl group undergo an unusual but facile P–C bond cleavage to form tetrasubstituted pyrazoles. In the second type of reaction, Me 3 SiN 3 reacts with the allenylphosphonates to form phosphono‐1,2,3‐triazoles in CH 3 CN at reflux, whereas (β‐azidoallyl)phosphonates were obtained in high yields at room temperature. These latter compounds undergo cycloaddition with activated acetylenes to afford multisubstituted 1,2,3‐triazoles. They were subsequently transformed into diverse N ‐substituted 1,2,3‐triazoles through the Horner–Wadsworth–Emmons reaction. The structures of the key compounds were established by X‐ray crystallography.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)