Extremely powerful chiral auxiliaries: Enantiomeric [4+2] cycloadducts of 2-oxazolone and 9,10-dimethylanthracene

Diastereoselective [4+3] Cycloadditions of Enantiopure Nitrogen‐Stabilized Oxyallyl Cations

“…[15] Applying our five-step sequence to 4a and 5a yielded the expected α-bromo ketones 4 and 5, respectively, in good overall yields. To our delight, both auxiliary-bound oxyallyl precursors afforded [4+3] cycloadducts with excellent diastereoselectivities, and chemical yields (Table 3).…”

“…These auxiliaries were reported to induce exceptional facial discrimination, particularly in Diels-Alder reactions and organocuprate conjugate addition. [15] Given these successes, it was felt that these types of auxiliaries should be investigated in our [4+3] cycloadditions.…”

New Routes to Chiral Evans Auxiliaries by Enzymatic Desymmetrisation and Resolution Strategies

“…Given the high diastereomeric excess obtained in aldol reactions with TiCl 4 [28] and ClTi(O-i-Pr) 3 , [29] we decided to investigate the use of Ti-enolates, particularly a tetrachlorotitanium-enolate generated by diisopropylethylamine. Instead of using the racemic auxiliary directly, we simplified the matter.…”

“…Aside from the (S)-substituted 2-oxazolidinones readily available from naturally occurring a-amino acids such as l-valine and l-phenylalanine, [2] their configurational antipodes are less accessible. The sterically constrained, designed chiral 2-oxazolidinones, such as 4,5-disubstituted-2-oxazolidinones conformationally fixed by bicyclo[2.2.1] and bicyclo[2.2.2] systems, [3] are also less easily available. That explains why since 1981 much work has been published about the use of novel Evans-type chiral auxiliaries, chemically designed and from sources other than natural a-amino acids.…”

Synthetic Versatility of 2-Oxazolone Heterocycle for Stereo-controlled Construction of 2-Amino Alcohols.

“…On the other hand, the treatment of 3-[(1S, 2R)-2-alkoxy-1-apocamphanecarbonyl]-2-oxazolone (58) with cyclic dienes at 139°C yielded the [4+2]cycloadducts 6 0 and 61 with reasonable diastereoselectivity (ref. 14,15,16). It is noteworthy that the uncatalyzed reaction of 2-propoxy-1 -apocamphanecarbonyl compound (5 8, R'=Pr) with anthracenes (55) proceeded with excellent diastereoselectivity above 94 %d.e.…”