Bromides, acyl, from aldehydes

In contrast to eq. 2.29, eq. 2.30 shows the oxidative conversion of aldehydes (62) to amides (63) via acyl bromides with NBS/AIBN/R2NH under refluxing conditions in CC14 [74]. The reaction comprises of the abstraction of the formyl hydrogen atom by the succinimidyl radical, bromine atom abstraction from NBS by the acyl radical, and lastly,... 

Reduction of Acyl Derivatives to Aldehydes. Aroyl chlorides and bromides give modest yields of aryl aldehydes when refluxed in diethyl ether with triethylsilane and Aluminum Chloride. Better yields of both alkyl and aryl aldehydes are obtained from mixtures of acyl chlorides or bromides and triethylsilane by using a small amount of 10% Palladium on Carbon catalyst (eq 7). This same combination of triethylsilane and catalyst can effect the reduction of ethyl thiol esters to aldehydes, even in sensitive polyfunctional compounds (eq 8). ... 

Under the influence of the triamine-Al catalyst, in situ generated ketene (formed from acyl bromide and diisopropylethy-lamine) reacted with aliphatic or aromatic aldehydes, affording -lactone in excellent yield and 88 96% ee (eq 5). AAC reactions deliver enatioeniiched -lactone acetate aldol surrogates, which are direct progenitors of numerous chiral building blocks (/S-amino acid, allene, and Q , -disubstituted carboxylic acids ). 

As noted earlier, [HCr(CO)5] also converts alkyl halides to alkanes, but the reactivity of the acyl chloride is much higher, such that it was possible to selectively convert the acyl chloride to an aldehyde in one step, without interference from the alkyl bromide functionality. A second equivalent of [HCr(CO)5] further reduced the alkyl bromide (Eq. (27)). 

Carbon atom 2 of the oxazole ring is also supplied by aldehydes in their reaction with a- (hydroxylamino) ketones, which proceeds in the presence of sulfuric acid and acetic anhydride (equation 109). Three further oxazole syntheses involving incorporation of a C(2) fragment are the condensation of triethyl orthoformate with the hydrochlorides of a-aminoacetophenones (equation 110), the reaction of acyl chlorides with a-azido ketones or a-azido esters in the presence of triphenylphosphine (equation 111), and the preparation of 2-aminobenzoxazole and benzoxazoleimines from o-aminophenols and cyanogen bromide (equation 112). 

Carbonylferrate salts, such as K [HFe(CO)4] , which is readily prepared from [Fe(CO)s] and ethanolic KOH, react with alkyl bromides or iodides to form alkyliron complexes. Under ambient conditions these complexes undergo insertion of CO and, in the presence of excess CO, aldehyde is eliminated and [Fe(CO)s] is regenerated (Scheme 10). Unfortunately, the reaction is not catalytic and the hydridocar-bonylferrate salt must be prepared in a separate step. Using the commercially available salt Na2[Fe(CO)4] a similar reaction takes place, but in this case the intermediate acyl complex is anionic and acid treatment is necessary to liberate the aldehyde (Scheme 11). ... 

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