SYNTHESIS OF POLYMER-SUPPORTED CHIRAL N-SULFONYLAMINO ACIDS AND THEIR USE IN ASYMMETRIC DIELS-ALDER REACTION OF CYCLOPENTADIENE WITH METHACROLEIN

Crosslinked polymer-supported chiral N-sulfonylamino acids have been synthesized by two methods; namely the chemical modification method and the copolymerization method. In the chemical modification method, the chlorosulfonyl group was introduced into styrene-divinylbenzene copolymers 1 by sulfonation with chlorosulfonic acid followed by chlorination with thionyl chloride. The degree of functionalization could be well controlled by the feed ratio of chlorosulfonic acid to aromatic rings of the polymer. Treatment of L-valine with the polymer having the chlorosulfonyl group 4 gave polymer-supported N-sulfonylated L-valine 5. An alternative approach to the synthesis of chiral polymers involves the copolymerization of monomers containing the desired chiral groups with styrene and divinylbenzene (DVB). Suspension copolymerization of chiral monomers 6, styrene, and DVB afforded the chiral polymers 7 in good yield. The N-sulfonylamino acid group in the polymer reacted with borane or monobromoborane to form chiral oxazaborolidinone 8, which catalyzed the Diels-Alder reaction of cyclopentadiene with methacrolein, leading to optically active cycloadduct having enantiomeric purity of 65% ee.