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The [32] cycloaddition of alkenyl Fischer carbene complexes 1 and 6 with diazomethane derivatives to give D 2 -pyrazoline carbenes 2, 4, and 7 is described. The conversion of (À)-8-phenylmenthol-derived carbenes 6 into pyrazoline esters 9 through a one-pot cycloaddition ± protection ± oxidation is presented as an expeditious route to enantiomerically pure 3-alkoxycarbonyl-D 2 -pyrazolines in good yields and in a highly regio-and diastereoselective manner. Pyrazolidines 13 were synthesized in excellent overall yields from 9 through pyrazolines 11 and 12, the diastereoselective reduction of CN bond being the key step. Azaprolines 16 and 17 were prepared in very good yields from epimeric trans-13 or cis-13 by oxidative deprotection of the silylated hydroxy group. In an alternative reaction, the pyrazolidine ring of 13 was reduced to obtain protected openchain 2,4-diamino alcohols 19 with three chiral centers.

The reaction of tert‐butylalkynyl chromium Fischer carbene complex 1 with nitrones 2 affords β‐enamino‐ketoaldehydes 4 by the light‐promoted rearrangement of the corresponding [3+2] cycloadduct carbene complexes 3. On the other hand, [3+2] cycloaddition of chiral nonracemic Fischer alkenyl carbene complexes 19 with nitrilimines 10 yields enantiomerically pure Δ2‐pyrazolines with high regio‐ and diastereoselectivity.

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