Reduction Luche

If it is assumed that the Mitsunobu glycosidation reaction described above proceeds through an SN2-type process with inversion of configuration at the anomeric position, then it follows that the desired / -glycoside can be formed selectively if pure a-lactol 17 is used in the reaction. Unfortunately, the /Mactol isomer of 17 is thermodynamically more stable than the a-diastereoisomer and is formed almost exclusively if the system is allowed to fully equilibrate. In the protic medium used for the Luche reduction, a signifi-... 

The total reduction of the enone system present in chromone to the corresponding chroman is effected by hydrogenation and is a key step during the synthesis of 2-(aminomethyl)chromans (2-AMCs) for evaluation of their affinity for the dopamine (DA) D2 receptor <1997JME4235>. Luche reduction of a chroman-4-one is used during the synthesis of antagonists of leukotrine D4 <1998BML1791>. 

The synthesis of the C9-C15 subunit 64 commenced with the cyclocondensation of aldehyde 67 and diene 68 to provide dihydropyrone 66 (Scheme 16) [118]. A Luche reduction [119, 120] and acid-mediated Ferrier rearrangement gave lactol 69 [121], installing the 03-04 (Z)-trisubstituted olefin. A further five steps... 

Sharpless catalytic asymmetric dihydroxylation of 2-vinylfuran followed by treatment of the diol product with NBS, and subsequent Jones oxidation and Luche reduction provided a highly functionalized a,(1-unsaturated y-lactone in 70% yield overall giving a key intermediate in the synthesis of phomopsolide C <02TL8195>. Similar procedures were adopted by the same authors to synthesize 2-deoxy and 2,3-dideoxyhexoses <02OL1771>. As depicted below, Sharpless kinetic resolution was also used to prepare a pyranone from a furfuryl alcohol in 38% yield, which served as the intermediate in the synthesis of (+)-isoaltholactone <02T6799>. 

Explain the stereoselectivity observed in the Luche reduction step j. 

The Luche reduction of compound 8 was non-selective, resulting, after step j, in the formation of separable epimers 9. How could the undesired epimer be recycled ... 

The asymmetric total synthesis of the natural enantiomer (—)-nakadomarin A was completed by Nishida et al. in 2004 (Scheme 8.12) [82]. Diels-Alder reaction between siloxydiene 173 and chiral dienophile 172 (prepared from L-serine in 10 steps [83]) gave the highly functionalized key intermediate hydroisoquinoline 174, which was subjected to Luche reduction, cyclization, and HCl treatment to furnish the tricyclic intermediate 175. Compound 175 was converted to 177 via ozonolysis cleavage of ring B followed by recyclization of the unstable bisaldehyde to a five-membered ring by aldol condensation. The Z-olefin 178 was obtained from Wittig reaction of 177, and was further converted to furan 180 via peroxide 179. The... 

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