Carbon tetrabromide reaction with aldehydes

Dibromoalkenes which have been prepared from aromatic or a,/3-unsatur-ated aldehydes (by treatment with carbon tetrabromide and triphenylphosphine) react with three molar equivalents of methylenetriphenylphosphorane to give propargylidenetriphenylphosphoranes Wittig reaction with aldehydes completes a convenient synthesis of the conjugated enyne system of predominant -geometry (e.g. Scheme 117). ... 

Tribromoethanol derivatives are also obtained by the reaction of carbon tetrabromide with aldehydes in the presence of stannous fluoride. 2,3-Di-O-acetyl-D-erythronolactone 16 is synthesized as shown below (II). 

Reaction of aldehydes with carbon tetrabromide and tin(II) fluoride gives adducts, formed by addition of the elements of bromoform across the carbonyl group, which may be hydrolyzed to acids. In this way, 2,3-0-isopropylidene-D-glyceraldehyde (19) was converted into a mixture of D-erythro (20) and D-//zreo-tetronolactones (21).40... 

A rather unusual ylide, 85, can be readily generated by the interaction of carbon tetrabromide with triphenylphosphine. Reaction of 85 with aldehydes furnishes 1,1-dibromoalkenes 86a. The latter compounds, under the action of BuLi, are transformed into lithium acetylides 86b and ultimately into substituted acetylenes 86c. This sequence is widely used as a reliable method for the preparation of various acetylenes from readily available aldehydes. 

The first step is carried out by either of two procedures. In one, the aldehyde (I eq.) is added to a mixture of iriphenylphosphine (4 cq.) and carbon tetrabromide (2 eq.) in methylene chloride at 0° with a reaction time of 5 min. In the second, preferred method, a reagent is prepared by the interaction of zinc dust (2 eq.), iriphenylphosphine (2 eq.), and carbon tetrabromide (2 eq.) in methylene chloride at room temperature for 24-30 hr. The aldehyde (1 eq.) is added to this reagent and the reaction is allowed to proceed for 1-2 hr. The yields by the second method are 80-90%. 

A solution of the aldehyde (10.5 g, 32.2 mmol) in dry ("HiCF (400 mL) was treated at room temperature with carbon tetrabromide (42.6 g, 128 mmol) and zinc dust (8.41 g, 128 mmol), followed by triphenylphosphine (33.7g, 128 mmol) in portions to keep the reaction temperature at 25 °C for another 1 h, diluted with hexanes (300 mL), fdtered through a thin pad of silica gel, and washed with pentane and ether. The combined organic layers were concentrated in vacuo. The crude product was purified by chromatography (silica gel) eluting with hexanes/EtOAc (10 1) to yield 13.5 g (87%) of the dibromoolefin as a colorless oil. 

French chemists have been able to increase the yields to 85-90% by use of a 40 60 mixture of THF—ether as solvent instead of pure THF. Note that Corey and Fuchs (4, 550) have prepared 1,1-dibromo-l-alkenes by the reaction of an aldehyde with triphenylphosphine, carbon tetrabromide, and zinc in methylene chloride. 

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