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ChemInform Abstract: A Highly Diastereoselective Intramolecular Hetero Diels—Alder Approach Towards Tetracyclic Pyrazoles.

✍ Scribed by E. CEULEMANS; M. VOETS; S. EMMERS; W. DEHAEN

Publisher
John Wiley and Sons
Year
2010
Weight
34 KB
Volume
29
Category
Article
ISSN
0931-7597

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✦ Synopsis

The pyrazole aldehyde (I) undergoes Knoevenagel condensations with heterocycles to yield adducts, which are directly thermolyzed to cyclize via hetero Diels-Alder reactions to cis-fused tetracyclic title heterocycles. Interestingly, the isoxazolo-fused cycloadduct (VII) is converted to the spiro-azirines (VIII) and (IX) on prolonged heating.

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The title compounds (III), (IV), and (VI) are synthesized by a hetero-Diels-Alder reaction using the sterically demanding diene (I) as a new building block. The effect of commonly used Lewis acids and the substitution pattern of various imines (II) on both the mechanism and the diastereoselectivity