Aldols haloacetyl aldol reactions

A Haloacetyl oxazolidinones form suitable enolate partners in aldol reactions, although complete aldehyde conversion requires the use of a slight excess of imide. Nucleophilic azide displacement of a-halo-P-hydroxy syn aldol adducts affords the corresponding anti a-amino- 3-hydroxy compounds. ... 

Chiral alcohol 73 was synthesized using the Evans aldol reaction and provided the syn-selective aldol adduct (95 5) in 52% yield in the haloacetyl aldol reaction during the total synthesis of (-)-clavosolide B. The chlorine atom was removed by treatment of Zn/NH4C1 in methanol, providing an additional example of an acetate aldol equivalent. 

Alternative routes to labeled anri-/3-hydroxy-a-amino acids of the a//o-threonine type are described in Section 11.3.9. They involve aldol reactions of haloacetyl-Evans and -Oppolzer auxiliaries to give iyn-/3-hydroxy-a-halo derivatives, whose a-halo groups are then inverted by nucleophilic displacement with azide ion. ... 

Chiral a-unsubstituted a,)8-unsaturated, isotopically carbon-labeled imides or esters (such as 249 above) needed as starting materials for such applications are best prepared by Horner-Wadsworth-Emmons reaction of e.p. (7 )-or-(5)-A-diethylphosphonoacetyl 4-substituted l,3-oxazolidin-2-ones or bornane-10,2-sultams or of (1R,2S,3R)/ (15,2R,35)-3-[A-phenylsulfonyl-A-(3,5-dimethylphenyl)amino]bornyldiefhylphosphono-acetates (e.g., 252) with aldehydes For purposes of isotopic synthesis, labels could be incorporated either via the haloacetyl group or the aldehyde component, or both, as suggested in Figure 11.87. Entities of the 249-type are also accessible through aldol reaction of the respective homochiral acetyl derivatives 253 with aldehydes, (9-acetylation of the resultant diastereomeric )8-hydroxy intermediates 254 and elimination of HO Ac upon treatment with Both methods avoid the separate preparation of labeled... 

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