Reactions on Chiral a,3-Unsaturated Imides and Esters

3-dipolar cycloadditions °, Pd(OAc)2-catalyzed cyclopropanations and OSO4- or RuCl3/NaI04-mediated bishydroxylations. These provide synthetic approaches to additional targets such as e.p. alicychc, heterocychc, a,/3-dihydroxylated and cyclopropanated carboxylic acid derivatives. 

Out of this arsenal of synthetic procedures, only Michael and Diels-Alder additions have been exploited so far for the preparation of e.p. compounds labeled with isotopic carbon or hydrogen. For applications in 1,4-additions, starting materials derived from Oppolzer s and Helmchen s auxiliaries have shown some superiority to the original Evans derivatives, though most weak points of the latter have been overcome by utilizing the C4-phenyl auxiUary (Xcpo) instead of the isopropyl (Xqpo) or benzyl (Xcbo) analogs. Nevertheless, the latter two have been more commonly used. 

Reaction conditions 1. MeCHO, DBU, LiBr, acetonitrile r.t., 3 h 2a. EtMgBr, 

Reaction conditions la. p CJMeLi or MeLi (2 equiv.), Cul.PBus, ether/toluene  

Significantly better yields (80-95%) and diastereoselectivities (to 98% d.e.) in 1,4-additions of organocuprates at the /3-position can be achieved by use of (IR,2S,3R)/ (lS,2i ,35)-3-[A -phenylsulfonyl-A -(3,5-dimethylphenyl)amino]boman-2-ol (Helmchen s auxiliary) in place of Oppolzer s auxiliary, and of RCu BFa (Yamamoto reagents) instead of 

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Sections 11.3.6-11.3.9 cover Type II reactions. Section 11.3.10, Reactions on Chiral a,/3-Unsaturated Imides and Esters , appears at the end because, although it is formally a Type I reaction, it utilizes as starting materials chiral haloacetates, which are for practical purposes Type 11 intermediates. 

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