Thionyl bromide, reaction with alcohols

In 1963, an asymmetric synthesis of chloroallenes was reported by the SNi reaction of propargyl alcohols with thionyl chloride [34]. Since then, rearrangement of pro-pargylic precursors has been one of the most useful methodologies for the synthesis of allenes [35]. Treatment of 84, obtained by asymmetric reduction with LiAlH4-Dar-von alcohol complex, with thionyl bromide gave 86 as the major product via 85 (Scheme 4.21) [36],... 

Alcohols can be converted to alkyl halides by reaction with thionyl chloride, SOCI phosphorous trichloride, PCI phosphorous pen-tachloride, PCI or phosphorous tribromide, PBr3. For example, ethyl chloride or ethyl bromide can be prepared from ethyl alcohol via reactions with sulfur and phosphorous halides. 

Now let s draw the forward scheme. Hydrolysis of the nitrile to the carboxylic acid, followed by reaction with thionyl chloride, produces the acid chloride. Reaction with excess methyl magnesium bromide, followed by water work-up, results in the formation of a tertiary alcohol, with the incorporation of two new methyl groups. The tertiary alcohol can then serve as a nucleophile in an acetylation reaction (upon treatment with acetyl chloride) to give the desired ester. 

Both reactants m the Williamson ether synthesis usually originate m alcohol pre cursors Sodium and potassium alkoxides are prepared by reaction of an alcohol with the appropriate metal and alkyl halides are most commonly made from alcohols by reaction with a hydrogen halide (Section 4 7) thionyl chloride (Section 4 13) or phosphorus tri bromide (Section 4 13) Alternatively alkyl p toluenesulfonates may be used m place of alkyl halides alkyl p toluenesulfonates are also prepared from alcohols as their imme diate precursors (Section 8 14)... 

Other halides that are useful in converting alcohols to alkyl halides are PC15, PC13, PBr3, and Pl3, which are acid halides of phosphorus oxyacids. As with thionyl chloride, a weak base often is used to facilitate the reaction. The base acts to neutralize the acid formed, and also to generate bromide ion for SN reactions ... 

Preparation. Several methods of preparation have been reported, but the most convenient is probably the reaction of CS with phenylmagnesium bromide or phenyllithium to give dithiobenzoic acid this is converted into thiobenzoyl chloride with thionyl chloride. Oxygen must be rigorously excluded or benzoyl chloride is formed. The reagent reacts with alcohols in dry pyridine to... 

The synthesis of the second fragment, the oleandrose disaccharide appendage, is outlined in Scheme 94 [206,207]. The sequence begins with the addition of vinylmagnesium bromide to 689, which produces a 5 1 mixture of diastereomeric alcohols 700. Without separation, these are quantitatively converted to the cyclic sulfite 701 upon deprotection and treatment of the resulting diols with thionyl chloride. Reaction of 701 with diiron pentacarbonyl under ultrasonic conditions produces a mixture of diastereomeric iron complexes which, when carbonylated at 230 atm, gives j5,y-unsaturated lactone 702. 

The mechanism for the reaction of phosphorus tribromide with alcohols is similar to that for the reaction of alcohols with thionyl chloride. The alcohol reacts with PBr3 giving an intermediate of the type ROPBr2 which reacts with the nucleophilic bromide ion. 

Alkyl halides are prepared by the reaction of alcohols with mineral acids (HCl and HBr) or with reagents such as thionyl chloride, thionyl bromide, PXg, and PXg. Alcohols are also prepared by the reaction of alkenes with HCl, HBr, or HI however, alkyl sulfates, alkyl nitrates, and alkyl perchlorates from those mineral acids tend to be unstable. 

Dibenzocycloheptenone (24-6) also serves as a starting material for the preparation of one of the few medicinal products that contains an acetylenic linkage. Reaction of (24-6) with the Grignard reagent from propargyl bromide leads to the alcohol (27-1). The free proton acetylene is sufficiently acidic for that center to take part in a Mannich reaction. Thus, reaction of (27-1) with formaldehyde and dimethylamine gives the adduct (27-2). Dehydration by means of thionyl chloride completes the synthesis of intriptyline (27-3) [28]. 

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