Selective magnesiation of chloro-iodopurines: an efficient approach to new purine derivatives.

[reaction: see text] Both 6-chloro-2-iodo-9-isopropylpurine (1) and 2-chloro-6-iodo-9-benzylpurine (4) undergo a selective I/Mg exchange reaction with iPrMgCl at -80 degrees C. The reaction course at 0 degrees C is different. Magnesiation of 1 proceeds with the migration of magnesium to the 8 position of the purine nuclei. In the case of 4, substitution of iodine with an alkyl group from the Grignard reagent accompanied with a Cl/Mg exchange reaction takes place, and 6-alkyl-2-magnesiated purines (9) are formed. Thus prepared Grignard reagents afford the corresponding alcohols by the reaction with aldehydes.