Chiral stereoinductive potential

One major advantage of chiral auxiliary reagents over chiral a-substituted reagents is the fact that the chiral diol or diamine unit is not modified in the bond-making process and is thus potentially recyclable. The preparation of enan-tiomerically pure a-substituted reagents requires a stereoinductive transformation... 

In one example particular stereochemical issues were addressed. Silyl enol ether 77 undergoes palladium-catalyzed 1,6-ECRC with a modest level of stereoinduction to afford a diastereomer-ic mixture [d.r. eisl trails) 2 1], These initial results should stimulate further investigation into transition-metal-catalyzed ECRCs and have the potential for future development of chiral metal catalysts for such processes. 

An early variant of the Nazarov cyclization119 employed an alkoxycarbonyl substituent and Lewis acid catalysis to facilitate the reaction. The cyclizations were described as temperamental", but did demonstrate the capability to facilitate the cyclization and control the site of the alkene in the cyclized product. For example, cyclization of the a,a -dienone 7 is promoted by the action of trimethylsilyl iodide to afford the /i-keto ester 8 in 48% yield. No studies in stereoinduction have been reported, but, given the recent advances in the design of chiral Lewis acids and the efficient chiral auxiliaries for the reactions of carboxylic acid esters, these substrates are potentially suitable candidates for such studies. 

Electrocyclic processes have been widely used for the predictable control of diene geometry and the control of vicinal stereocenters on cyclohexadicne rings. These reactions hold considerable potential for diastcreosclcctivc carbon carbon bond construction via stereoinduction from remote substituents. Yet as can be judged from this section, this aspect of the field is still in its infancy. There have been no reports of investigations into the efficacy of chiral auxiliaries or chiral catalysts. Perhaps it is the nonobvious nature of these carbon carbon bond constructions in the rctrosynthetic analysis of complex structures that has limited the scope of such investigations to date. It can be expected that future studies will rectify the oversight. 

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