Oxazolines, chiral, arylation

Asymmetric versions of the cyclopropanation reaction of electron-deficient olefins using chirally modified Fischer carbene complexes, prepared by exchange of CO ligands with chiral bisphosphites [21a] or phosphines [21b], have been tested. However, the asymmetric inductions are rather modest [21a] or not quantified (only the observation that the cyclopropane is optically active is reported) [21b]. Much better facial selectivities are reached in the cyclopropanation of enantiopure alkenyl oxazolines with aryl- or alkyl-substituted alkoxy-carbene complexes of chromium [22] (Scheme 5). 

RLi (R = alkyl, aryl, vinylic), sparteine or bis(oxazolines) (chiral)... 

Degnan, A. P., Meyers, A. I. Total Syntheses of (-)-Herbertenediol, (-)-Mastigophorene A, and (+)-Mastigophorene B. Combined Utility of Chiral Bicyclic Lactams and Chiral Aryl Oxazolines. J. Am. Chem. Soc. 1999,121,2762-2769. 

During recent years, substantial progress has been made in the hydrogenation of unfunctionalized alkenes. With iridium complexes derived from chiral phos-phino-oxazolines and related ligands, excellent enantioselectivities and high TON/TOF values can now be obtained for a wide range of unfunctionalized olefins. Most substrates studied to date have at least one aryl substituent at the... 

Bis(oxazoline)-copper complexes 158 have been used by Evans group as chiral catalysts for the enantioselective aziridination of olefins.116 Aryl-substituted olefins have been found to be particularly suitable substrates, which can be efficiently converted to A-tosylaziridines with ee of up to 97% (R = Ph... 

Preparation of the chiral biphenyls and binaphthyls with high enantiose-lectivity can be achieved via substitution of an aromatic methoxyl group with an aryl Grignard reagent using oxazoline as the chiral auxiliary.38 Schemes 8-10 and 8 11 outline the asymmetric synthesis of such chiral biaryl compounds. 

The proton abstraction typically requires strong bases although weaker bases can be employed if the a-carbon is substituted with an additional activating group, such as an aryl group. " ° Deprotonation of chiral arylmethyloxazolines followed by alkylation gave modest levels of diastereoselection (up to 60% de). " Deprotonation of appropriately substituted 2-(allyloxymethyl)oxazolines resulted in... 

The first general method allowing the preparation of optically active 3,3-dialkylpropionic acids via asymmetric synthesis is based on chiral oxazolines.37-41 The a,3-unsaturated derivatives (41), accessible as pure ( )-isomers from (40) and the respective aldehydes (RCHO), undergo highly selective 1,4-additions in a variety of cases (Scheme 16) when treated with alkyl- or aryl-lithium reagents. The products... 

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