Asymmetric Phase Transfer Reactions Catalyzed by Chiral Crown Ethers Derived from Monosaccharides

Sugar-based Crown Ethers in Enantioselective Syntheses

“…A few of them proved to be efficient catalyst in two Michael additions, in a Darzens condensation and in the epoxidation of α,β-enones. It was found that the type of the monosaccharide, the substituents on the sugar unit and on the nitrogen atom of the macroring have had a significant influence on both the yield and the enantioselectivity [5].…”

“…There is an optimum length for the hydrocarbon spacer connecting the MeO or Ph 2 P(O) moiety to the nitrogen atom of the azacrown ring. Among the catalysts tested, lariat ether 1e with a three carbon atom spacer [(CH 2 ) 3 -OCH 3 ] and macrocycle 1i with a four carbon atom chain [(CH 2 ) 4 -P(O)Ph 2 ] proved to be the best (90 % ee and 95 % ee, respectively) [5].…”

“…In the presence of 1d [R=(CH 2 ) 3 OH], the substituents in the aromatic ring of the chalcone (CH 3 , OCH 3 , NO 2 , Cl, F) resulted in a decrease in the optical yield (14-68 % ee), as compared to the case with the unsubstituted chalcone 26a (87 % ee). From among the α,β-enones analogue to chalcone, the 1-naphthyl derivative (Ar 1 =1-naphthyl-, Ar 2 =Ph) and trans-crotonophenone derivative (Ar 1 =Ph, Ar 2 =Me) were formed with the highest ee value (87 % and 76 %, respectively) [5,13].…”

“…5). The trans-epoxyketone (32) was obtained in general in a diastereomeric excess (de) of >98 %, with a configuration of (-)-(2R,3S) [5,8,14,[16][17][18]. The aromatic unit (Ar 1 ) of the α-chloro-carbonyl compounds (30) were phenyl-, 2-furyl-, 2-thiophenyl-, 2-pyrroyl.…”

“…A part of the starting monosaccharides is easily available commercial product. Crown ethers containing a sugar unit incorporated in the macrocyclic ring may be built from various monosaccharides; thus macrocycles of different chirality are available [4][5].…”