3-Chloro-2-buten

In a 3-1. three-necked round-bottomed flask fitted with a reflux condenser and a mercury-sealed stirrer, 250 g. (2 moles) of 1,3-dichloro-2-butene (Note 1) and 1.25 1. of 10% sodium carbonate are heated at reflux temperature for 3 hours. The 3-chloro-2-buten-l-ol is extracted with three 300-ml. portions of ether, which are then dried over anhydrous magnesium sulfate. The ether is removed by distillation through a 20-cm. Fenske column, and the residue is distilled from a 250-ml. Claisen flask, yielding 134 g. (63%) of 3-chloro-2-buten-l-ol, b.p. 58-60°/8 mm., 1-4670. 

Treatment of 3-chloro-2-buten-l-ol with NaNHa gives primarily 2-butyn-l-ol rather than 2,3-butadien-l-ol. Using SpartanView to obtain the energies of the two products, tell whether the lower-energy molecule corresponds to the observed product. 

Stoik et al. have shown that heteroannular extended dienolates such as (73), which contain substituents at both the a- and y-positions, undergo predominantly equatorial alkylation (Scheme 35). The dienolate (73) was product by lithium-ammonia reduction of the tricyclic dienone (72) and the product of its alkylation wiA I-bromo-3-chloro-2-butene and hydrolysis of the resulting enol ether, i.e. (74), was a key intermediate in a short, highly stereoselective synthesis of ( )-adrenosterone. It was pointed out that equatorial alkylation is obtained with dienolates such as (73) and related compounds brcause a peri interaction (Me OMe) of the a- and y-substituents forces the ring a to adopt a half-boat conformation in which the a-face of the ir-system is accessible to attack. 

NaNH2 is also a basic reagent of choice for dehydrohalogenation. Dehydrohalogenation is easily achieved by treatment of bromo- or chloroaliphatic or bromovinylic compounds with a suspension of NaNH2. For example stearolic acid (ref. 48), 10-undecynoic acid (ref. 49) or diethoxy acetylene (ref. 50) have been so prepared (Fig. 9). In the same conditions phenylacetylene has been obtained from 2-bromostyrene (ref. 51), 2-butyn-l-ol from 3-chloro-2-buten-l-ol (ref. 52) but more drastic conditions are required to prepare cyclohexylpropyne from the corresponding vinyl bromide (ref. 53). 

Moisture must be completely excluded because sodamide readily becomes coated with sodium hydroxide it is thus advisable to prepare the reagent shortly before use by reaction of sodium with anhydrous liquid ammonia192 in the presence of iron(m) chloride or nitrate.190 2-Butyn-l-ol (7) is then obtained in 80% from 3-chloro-2-buten-l-ol (6) by way of its sodium salt, the original starting material being l,3-dichloro-2-butene 193... 

Butyn-l-ol Biacetyl Methyl acrylate l-Chloro-2-methyl-l-propene a-3-Chloro-2-buten-l-ol / -3-Chloro-2-buten-l-ol... 

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