Diastereofacial selectivity chiral lactones

The catalyst played an important role in the asymmetric synthesis of Corey lactone based on high diastereofacial selective Diels-Alder reaction between chiral acrylate 37 and 5-benzyloxymethylcyclopentadiene [41] (Equation 3.9). The cycloadduct 38 was then converted into chiral Corey lactone [42] by a three-step procedure. 

Lactone enolates typically show poor simple diastereoselection. For example, in connection with a synthesis of ( )-podorhizol, Ziegler and Schwartz added the lithium enolate of butyrolactone (82) to 3,4,5-trimethoxybenzaldehyde (equation 74). Although the diastereofacial selectivity of the chiral enolate is complete, aldols (83) and (84) are formed in a ratio of 50 50 in THF and 25 75 in an equimolar mixture of dimethoxyethane and ether. ... 

The very low diastereofacial selectivity observed with lactone 36 may be ascribed to the competing effects of two chiral centers, the allylic oxygen atom 0-4 (favored si-face attack) and the C-5 methyl group (favored re-face attack). 

The alternative strategy of using d,v-aminoindanol as a chiral auxiliary on the Michael donor has also been explored.81 Chiral amide enolates were reacted with a,P-unsaturated ester 70, and the resultant adducts were reduced and cyclized to 8-lactones 73 to determine the facial selectivity on the Michael acceptor. It is interesting that protected amino alcohol 71 did not lead to significant diastereofacial discrimination, whereas 72 afforded lactone 73 with high 4-(,S )-selectivity (Scheme 24.15). 

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