Hydrogen chloride reaction with allene

Secondary and tertiary propargyl alcohols are directly converted to halo-allenes on reaction with concentrated aqueous hydrogen halides in the presence of the corresponding cuprous halide [60,72-73]. (See Table VII.) Better yields are obtained with hydrogen bromide. Hydrogen chloride yields chloroallene, propargyl chloride, and the chloro- 1,3-diene isomers (Eq. 60). 

Propargyl alcohols may be converted to allenes by several methods, for example, (a) through the intermediate formation of propargyl halides which are not isolated but react directly with cuprous salts and hydrogen halide [60, 72-73] or cyanide [71] (b) typical alcohol reactions with thionyl chloride [74a-d] phosphorus halides [75-77], and miscellaneous reagents (see Scheme 3). 

Related to ketene cycloadditions are the group of cycloadditions with vinyl cation intermediates. The reaction between 2-butyne 6.120 and chlorine giving the dichlorocyclobutene 6.122 is the Smirnov-Zamkow reaction, and there is a similar reaction between allene 6.123 and hydrogen chloride giving the... 

From the above discussion, it is clear that a vinylium ion can participate as the TT a component in the concerted [tt s + rr a] cycloaddition. For example, allene reacts with hydrogen chloride at —70 °C to give a mixture of the ste-reoisomeric l,3-dichloro-l,3-dimethylcyclobutanes. In this reaction, an initially formed cation combines with a molecule of allene by the [tt s + rr a] route to give another cation, which reacts with chloride ion and hydrogen chloride to afford the observed products. 

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