By G. R. Stephenson, J.-P. Genet (auth.), G. R. Stephenson (eds.)
Asymmetric synthesis is among the most important strategic matters in natural chemistry, and this booklet describes complex recommendations and their purposes to the economic and laboratory synthesis of vital chiral molecules. The overseas crew of hugely revered authors offer rigorous and concise reports in their components of expertise.
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A catalyst with only 12% ee showed low catalytic activity, and (54) was obtained with 11% ee. , ~~ % H o N H H S2 NC \ ", H 0- -0 C-OH + HCN S2 (2mol%) S3 .. 17 However, the initial presence of small amounts of optically active product led to catalyst activation and chirality amplification. Dipeptide (52) with 12% ee now gave the cyanohydrin (54) with an ee of 87%. These observations suggest that a complex composed of both dipeptide and product is the actual catalyst, and that this species of unknown composition is catalytically much more active than (52) alone.
Ph) H ~yY~e Me N - o Y 000 •••• Me """ 0 0 OTBS 6Me I. TICI4• i-Pr 2NEI, CH2Cl 2• -20°C. Ih; Cool to -78°C. 5 h (93%) 2. AcOH. 4 o 0 ~l;:;h ~i:;6o. ~ oi~~:~OH' TI W . , 18h. (76%) Y00 Me Me Me (> 99% de) H20 . 90°C. 4h (43%) ::::::.... 5 43 - "/NVR RCHO. 6 the corresponding tri-n-butylstannyl enolates are utilised for the same purpose, syn-aldol adducts are also obtained with high diastereocontrol but 31 CHIRAL ENOLATES with an opposite sense of asymmetric induction, presumably because of the occurrence of internal chelation between the sultam oxygen and the tin moiety during the aldol transition state; a possibility denied to the boron enolates.
RCHO. lSOC. 40 min. 20 Base hydrolysis allows the (R)-triphenylethane diol auxiliary to be removed in excellent yield without loss of optical purity in the fJ-hydroxy acid. 21 Despite the rather obvious synthetic advantages I. 11 that this type of approach offers when compared with chiral auxiliary-based methods, organic chemists were rather slow to embrace these concepts, a fact that in hindsight now seems rather astonishing! V These chiral complexing agents enable highly reactive chiral tin(II) enolates to be generated from a variety of N-acylated thiazolidines.