D03 Lewis Acid Catalyzed Diazo Cycloadditions

Lewis Acid Catalysis in Diazo Cycloadditions:
As preliminary works, we have examined the Lewis acid catalysis in diazo cycloadditions. Trimethylsilyldiazomethane and 3-crotonoyl-2-oxazolidinone are selected. This reaction can be accelerated in the presence of a variety of Lewis acids. Especially, titanium catalysts are effective, both in rate enhancement and product selectivity.

DBFOX/Ph Complex Catalyzed Asymmetric Diazo Cycloadditions:
No previous examples are known for the catalyzed asymmetric cycloadditions of diazoalkanes. Although titanium taddolate catalysts accelerate the reaction, the enantioselectivity observed did not exceed 55% ee. However, the combination of DBFOX/Ph - metal perchlorate complexes with 3-(2-alkenoyl)-2-oxazolidinones is found to be highly effective for this purpose. The best catalyst found is the aqua DBFOX/Ph complex of zinc(II) perchlorate together with MS 4A. At -40 ÁC, the 1-acetyl-4-methyl-2-pyrazoline-5-carboxylic derivative is obtained in 87% yield with an enantioselectivity of 99% ee.

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