Halides carbonyl dibromide

Reactions of carbonyl dibromide with other carbon halides... 

Carbonyl dibromide reacts with the other carbonyl halides, upon heating in an autoclave, according to [902,905] ... 

Complexes of other metals are also capable of catalyzing useful carbonylation reactions under phase transfer conditions. For example, certain palladium(o) catalysts, like Co2(C0)g, can catalyze the carbonylation of benzylic halides to carboxylic acids. When applied to vinylic dibromides, unsaturated diacids or diynes were obtained, using Pd(diphos)2[diphos l,2-bis(diphenylphosphino)ethane] as the metal catalyst, benzyltriethylammonium chloride as the phase transfer agent, and t-amyl alcohol or benzene as the organic phase(18),... 

The key butenolide needed by Buszek, for his synthesis of (—)-octalactin A, had already been prepared by Godefroi and Chittenden and coworkers some years earlier (Scheme 13.4).9 Their pathway to 10 provides it in excellent overall yield, in three straightforward steps from l-ascorbic acid. The first step entails stereospecific hydrogenation of the double bond to obtain L-gulono-1,4-lactone 13. Reduction occurs exclusively from the sterically less-encumbered ot face of the alkene in this reaction. Tetraol 13 was then converted to the 2,6-dibromide 14 with HBr and acetic anhydride in acetic acid. Selective dehalogenation of 14 with sodium bisulfite finally procured 10. It is likely that the electron-withdrawing effect of the carbonyl in 14 preferentially weakens the adjacent C—Br bond, making this halide more susceptible to reductive elimination under these reaction conditions. 

In 1983, Nokami et al. observed that water had an accelerating effect on the aUylation of carbonyl compounds with diallyltin dibromide in ether. For example, benzaldehyde was aUylated in 75% yield in 1.5 h in a 1 1 mixture of ether/water, while the same reaction gave less than 50% yield in a variety of organic solvents such as ether, benzene, or ethyl acetate, even after a reaction time of 10 h. The tin reaction can be activated by using a combination of tin metal and a catalytic amount of hydrobromic acid. In this case, the addition of metallic aluminum powder or foil to the reaction mixture dramatically improved the yield of the product. The use of allyl chloride for such a reaction, however, was not successful The reaction can also proceed intramolecularly and ketones having allylic halide functionality were cyclized to form five- and six-membered rings.Similar intramolecular reactions occurred stereoselectively with aldehydes (Eq. 4.9). ... 

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