Luche’s conditions

Luche s conditions [71] for the reduction of 124 delivered the unstable allylic alcohol (134), which was quickly treated with TBSCl and EtsN to afford 135 in 70% yield for the two steps (Scheme 31). This 5-step reaction sequence from 125 proved to be usable in sizable quantity ( 20 g) and it also offered the advantage of starting with a simple and commercially available chiral moiety (S-glycidol). 

Dehydration and reduction of the resulting cyclohexenone under Luche s conditions gave the corresponding allylic alcohol. Esterification with an acid representing the C39 to C26 part of rapamycin gave compound 389. Finally, Ireland-Claisen rearrangement gave the branched-chain cyclohexane 390. 

Sodium borohydride is sometimes used in conjunction with CeCl3 (Luche s reagent).70 The active reductants under these conditions are thought to be alkoxyborohydrides. Sodium cyanoborohydride is a useful derivative of sodium borohydride.71 The electron-attracting cyano substituent reduces reactivity and only iminium groups are rapidly reduced by this reagent. 

Unfortunately, for whatever reason, Dupuy and Luche s improvements have not caught on. Most publications surveyed by this reviewer still used the classic Wharton conditions. 

B. Zemva, A. Jesih, K. Lutar, In Chemical Processes, Reactions under Extreme or Non-classic Conditions, J.L. Luche, C. Balny, S. Benefice, J.M. Denis, C. Petrier (Eds.), European Commission, COST Action D6, 1996, p. 153. 

The second pathway is analogous to the reaction of an activated metal, similar to those generated using Riecke s methodology, with alkyl halides. However, Luche reports that pre-activation of the zinc gave poor yields of organozinc under sonochemical conditions. 

Of great interest is the use of Oppolzer s camphorsultam as chiral auxiliary in a zinc-mediated allylation of oximes in the Luche conditions ... 

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