Amides A-halo

More recently, the same group has used a simpler and more easily prepared chiral ammonium phase-transfer catalyst 99 derived from BINOL in asymmetric Darzens reactions with a-halo amides 97 to generate glycidic tertiary amides 98 (Table 1.13). Unfortunately the selectivities were only moderate to low [48]. As mentioned in Section 1.2.3.1, tertiary amides can be converted to ketones. 

Reaction between a-hydroxy or a-halo amides and NaOBr... 

These conditions can also be applied to enolates prepared from a-halo amides. 

Oxazolidinediones can be obtained from electrochemical reduction of a-halo amides in the presence of carbon dioxide. Originally, the 2,4-oxazolidine-... 

A-halo electrophiles (TV-halo amines, A-halo amides and iV-halo imides) react with alkenes such as 1-hexene, cyclohexene and styrene in the presence of boron trifluoride to give halofluorides and A-halo adducts (equation 34)51. These types of reactions have been dis-... 

A useful preparation of A-acylureas initiated by the addition of A-halo amides to isocyanides was described (equation 35)53. / -Keto-a-(phenylthio)alkyl p-tolyl sulfones in... 

Photochemical Addition of A -Halo Amides and A -Halo Imides to Alkenes General Procedure62> 3 ... 

Condensation of Carbonyl Compounds with a-Halo Amides (Refot-matsky)... 

A similar reaction has been carried out on A-halo amides, which give y-lactones ... 

The most commonly used nonoxidative method used by chemists prior to 1958 is the substitution reaction using either chiral a-amino acids (L = NH3) or a-halo amides (L = F, Cl,... 

The intermediate a-amide radical generally prefers an s-cis orientation 13, minimizing allylic strain. However, when R is small, allylic strain is decreased and the s-trans conformation 14 is more accessible (Eq. 5). The lower selectivity generally observed with the a-bromide substrates is presumably due to the fact that the a-halo amide carbonyl is not as good a donor as the a, 5-unsaturated amide carbonyl and that this may be adversely affecting interactions with the chiral Lewis acid. No selectivity was observed using these conditions when R = H. 

Addition of HOX by means of A-halo amides is important for, inter alia, steroid syntheses. A 9(ll)-double bond adds OH at position 11 (11/S-OH) and Br at position 9 (9oc-Br). Solvents used are mixtures of water with acetone, dioxane, pyridine, or tert-butyl alcohol. 0.46N-perchloric acid has proved particularly suitable as acid since it reduces any tendency to formation of halohydrin esters.295... 

Regeneration of the carbonyl group can entail a trial-and-error process with the many procedures available. " Hg" salts and A(-halo amides remain the most frequently employed reagents. Aqueous lodomethane is a mild alternative. Epimerization at an a stereocenter does not normally attend the formation or removal of the dithianyl group (eqs 8, 9, 12, 13). 

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