Lewis Acid-Catalyzed 1,3-Dipolar Cycloaddition Reaction

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Unprecedented Lewis acid catalyzed stereo- and regiocontrol of 1, 3dipolar cycloaddition reactions have been achieved. Major results are as follows: 1) Lithium Z-enolates derived from (alkylideneamino)acetates act as 1, 3-dipoles in reactions to alpha,beta-unsaturated carbonyl compounds to give pyrrolidine-2-carboxylates in a highly stereoselctive fashion; 2) (Alkylideneamino)acetates derived from bulky aldehydes or ketones undergo anti-selective Michael additions to alpha,beta-unsaturated carbonyl compounds; 3) Michael additions using camphor imines of glycinates as donors are exclusively diastereoselective when beta-substituted alpha,beta-unsaturated carbonyl acceptors are used as acceptors; 4) Dipole/Lewis acid complexes are formed on treatment of hydroximoyl or hydrazonoyl chlorides with organometallics; 5) Nitrile oxide/MgBrCl complexes show high syn-selectivities in reactions with 2-(1-hydroxyalkyl)acrylates; 6) Nitrile oxide cycloadditions to magnesium alkoxides of alpha-chiral allylic alcohols proceed in a highly syn-selective manner; 7) Magnesium alkoxides of internal allylic alcohols are exclusively regioselctive in nitrile oxide cycloadditions to give isoxazoline-5-methanol derivatives; 8) Nitrile oxide cycloadditions to magnesium alkoxides of allylic alcohols are greatly accelerated; 9) Similar rate acceleration, regio- and stereocontrol are observed in Lewis acid-catalyzed nitrone cycloadditions to allylic alcohols.Through the present research, it is now clear that employment of an appropriate Lewis acid catalyst in dipolar cycloadditions leads to great enhancement of reaction rate and high improvement of stereoselectivity and regioselectivity. It is quite certain that this new methodology will open an entry to wide synthetic applications of dipolar cycloaddition reactions in organic synthesis.