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.
