Cyclohexyl-based chiral auxiliaries

A study on the effectiveness of various cyclohexyl-based chiral auxiliaries in the asynunetric addition of Grignard reagents to 1-acylpyridinium salts 45 has been published <96TL(37)3807>. 

Cyclohexyl based chiral auxiliaries have been widely employed in asymmetric syntheses170. Barluenga and coworkers171 reported the first chiral 2-alkoxy-l,3-butadienes of... 

Examination of Scheme 27 (22 total chiral auxiliaries employed) indicates that aryl chiral auxiliaries (as in 42) are more effective than alkyl chiral auxiliaries (as in 43) within zeolites. Replacing the phenyl part in 42 by the cyclohexyl moiety as in 43 had a dramatic effect on the observed stereoselectivity. The diastereoselectivity dropped from 80% to 29% in LiY. Replacing the phenyl group by the naphthyl group (44 another aryl chiral auxiliary) gave 70% de in LiY. Aryl chiral auxiliaries, 45 and 46 based on aminoalcohols gave 60% and 89% de, respectively. 

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