Acidified Alcohols as Agents to Introduce and Exchange Alkoxyls on the Periphery of Helicenes

Alcohols containing HCl transform the hydroquinone reduction-products of helicenebisquinones into p -alkoxyphenols that have the alkoxyls specifically on the peripheries of the helices. The reactions are quick, and the yields are high. Alkoxyls at the 6-position are replaced also, but only after 2 h at 60 °C, not after the 5 min at 25 °C sufficient to replace the peripheral hydroxyls of the hydroquinones. After the remaining inside hydroxyls of a dihydroxytetramethoxy[6]helicene prepared by this procedure have been converted into camphanates, one diastereomer crystallizes from solution, allowing an enantiomer resolution to be carried out on a large scale. By then simply reapplying the procedure with alcoholic acid, a variety of resolved dihydroxytetraalkoxy[6]helicenes can be prepared in excellent yields without resolution procedures having to be developed for each. Similar procedures are effective when applied to a [7]carbohelicene.