Crotonyl oxazolidinones

Lewis-acid-catalyzed asymmetric hetero-Diels-Alder cycloaddition of a 1-thiabuta-1,3-diene with chiral A/-acryloyl and A/-crotonyl oxazolidinone dienophile [105]... 

Asymmetric Diels-Alder reactions. Unlike methyl crotonate, which is a weak dienophile, chiral (E)-crotonyl oxazolidinones when activated by a dialkylaluminum chloride (1 equiv.) are highly reactive and diastereoselective dienophiles. For this purpose, the unsaturated imides formed from oxazolidinones (Xp) derived from (S)-phenylalanol show consistently higher diastereoselectivity than those derived from (S)-valinol or (IS, 2R)-norephedrine. The effect of the phenyl group is attributed in part at least to an electronic interaction of the aromatic ring. The reactions of the unsaturated imide 1 shown in equation (I) are typical of reactions of unsaturated N-acyloxazolidinones with cyclic and acyclic dienes. All the Diels-Alder reactions show almost complete endo-selectivity and high diastereoselectivity. Oxazolidinones are useful chiral auxiliaries for intramolecular Diels-Alder... 

Sibi s group studied a similar reaction using ligands 9b, 34a-c, and 161 with iodides 157b and 157c, tributyltin hydride 160 and A-crotonyl oxazolidinone 80a or A-cinnamoyl oxazolidinone 80b.As shown in Table 9.29 (entries 7 and 9), the inda-box ligands exhibited optimum results with yields up to 92% and selectivities up to 93% (ee). The use of the ligand-metal complexes in catalytic amounts led to lower yields and enantioselectivities (Fig. 9.50). ... 

A series of chiral bis(oxazoline) ligands, A, B, and C, differing in the length of the chain connecting the chiral oxazoline subunits and in the nature of the substituent at the chiral center, were examined in the M(OTf)2 (M = Zn, Mg, Cu) catalyzed reaction of A-crotonyl oxazolidinone with cyclopentadiene [34] (Eq. 8A.18). A l,4-bis(oxazoline) ligand C proved best for... 

An excellent asymmetric induction has also been observed by Snider et al. [164] in a hetero Diels-Alder reaction with the N-crotonyl oxazolidinone 2-172 which had already been used by Evans for the all carbon cycloaddition [ 164b]. Reaction of isobutene with 2-172 in the presence of Me2AlCl for 40 h at -30 °C in CH2C12 provided a mixture of the alcohol 2-174 and the lactone 2-175 via the primarily formed cycloadduct 2-173. Treatment of the mixture with sodium carbonate gave the lactone 2-175 as a pure enantiomer (Fig. 2-48). 

Kanemasa et al. reported an asymmetric conjugate addition reaction of thiol to A-crotonyl oxazolidinone in the presence of Ni(II)-DBFOX/Ph catalyst [20] (Table 8.2). In this reaction. Proton Sponge (1) is indispensable for high enantioselectivity, and thioether was obtained in 84-99% yield with 91-94% ee. 

DC reactions of mcsitonitrile oxide and C, -diphenyl nitrone with the resin-bound chiral iV-crotonyl-oxazolidinone 49 in the presence of different amounts of Mg(II) cation were reported. The study showed that the isoxazoline and isoxazolidine adducts can be obtained on solid-phase, but with lower selectivity and yield than the corresponding product synthesised in solution <01T8313>. 

The [4+2] cycloaddition of A -crotonyl oxazolidinones with alkenes at low temperature in the presence of Me2AlCl as Lewis acid leads to 8-lactones stereoselectively. 

The aldol reaction illustrated in eq 2 has been applied to the targeted synthesis of a number of complex molecules including Tylosin, Hapalosin, the antibiotic Sinefungin, and the HIV protease Saquinavir inhibitor. Oxazolidinone-type chiral auxiliaries derived from 1 have also been employed for the control of Diels-Alder reactions of attached acryloyl or crotonyl groups. ... 

Asymmetric conjugate addition of thiols to 3-crotonyl-2-oxazolidinone is effectively catalyzed by the aqua nickel(II) complex of (i ,l )-DBFOX/Ph to produce conjugate adducts in high chemical yields and with high enantioselectivity [125] (Sch. 27). 

Enantioselective addition of 3-crotonyl-2-oxazolidinone 423 to 1 under double catalytic conditions using 2,2,6,6-tetramethylpiperidine (TMP) and R,R-complex of nikel(II) perchlorate hexahydrate in THF... 

The Evans aldol reaction of chiral, crotonyl-substituted oxazolidinones had proven effective for the asymmetric synthesis of hydroxypropionates... 

Iwasa and Nishiyama reported catalytic enantioselective 1,3-dipolar cycloaddition reactions of nitrones using chiral Mg(II) complexes (Scheme 4.7) [5]. They synthesized chiral tridentate bis(2-oxazolinyl)xanthene ligands (Xabox, 19) and the chiral environments were evaluated in the 10mol% Xabox-Mg(Cl04)-(H20)6-catalyzed enantioselective 1,3-dipolar cycloaddition of nitrones (1 equiv) with 3-crotonyl-2-oxazolidinone (1 equiv). The reactions of (16) and (17) in dichloromethane at 10 °C proceeded smoothly to give the corresponding adduct (18) with 92% ee and an endo exo ratio of > 99 1. 

---