CATALYZED ASYMMETRIC 1,3-DIPOLAR CYCLOADDITION REACTIONS

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The central purpose of the present project research is the establishment of catalyzed asymmetric 1,3-dipolar cycloaddition methodology, which provides an important entry to stereoselectivesynthesis of heterocyclic compounds. A llylic alcohol substrates have been employed in nitrone and nitrile oxide cycloadditions to give the following findings :1. Benzonitrile oxide cycloadditions with allylic alcohols can be accelerated in the presence of magnesium ions.2. High syn selectivity is observed in the magnesium ion catalyzed reactions of allylic alcohols bearing an alpha-chiral center.3. High regioselectivity is observed in the magnesium ion catalyzed reactions of allylic alcohols bearing gamma-substituents.4. Higher rate acceleration is observed in the magnesium ion caralyzed reactions of more substiituted allylic alcohol substrates. The substrate having two methyl substituents at the gamma-position is 16000 times faster than the unsubstituted one.5. The maximum catalytic cycle of 34 has been recorded in the magnesium ion catalyzed reactions between mesitonitrile oxide and allyl alcohol.6. The presence of a stoichiometric amount of bis (diphenylmethylsilyl) ether of (R,R)-1,2-diphenyl-1,2-ethanediol in the above reaction did not induce any enantioselectivity.7. Other chiral ligands such as bis (diphenylmethyl) ether and bis (triphenylmethyl) ether of (R,R)-1,2-diphenyl-1,2-ethanediol have been employed in the asymmetric reactions to give poor results.8. Use of crotyl alcohol, instead of allyl alcohol, in the magnesium ion catalyzed reactions in the presence of the above chiral ligands result in the inhibition of reaction.9. The nitrone cycloadditions using 3-acryloyl-2-oxazolidinone in the presence of DBFOX-modified magnesium ion are highly enantioselective, but the nitrile oxide cycloadditions can not find rate acceleration either.