Journal
TETRAHEDRON LETTERS
Volume 60, Issue 44, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.tetlet.2019.151206
Keywords
Lewis base; Spirocyclo-pentane pyrazolone; Pyrano[2,3-c]pyrazoles; Annulation
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Funding
- National Natural Science Foundation of China [21276238, 21706234]
- Natural Science Foundation of Zhejiang Province of China [LY198060011]
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An effective Lewis base catalyst-controlled alpha-regioselective annulation reaction of gamma-substituted allenoates with unsaturated pyrazolones has been developed, affording various spirocyclopentene-pyrazolones and pyrano[2,3-c]pyrazoles. The combination of PPh3 and K2CO3 promoted the [3+2] annulation to access the spirocyclopentene-pyrazolones in moderate to good yields (up to 90%) with excellent diastereoselectivities (dr >19:1), while [4+2] annulations to generate pyrano[2,3-clpyrazoles were successfully achieved by employing DBU as catalyst (in up to 92% yield). Of importance, the asymmetric synthesis of spirocyclopentene-pyrazolone was realized by using our previously reported chiral ferrocenylphosphine catalyst. (C) 2019 Elsevier Ltd. All rights reserved.
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