Diiodosilane. 2. A Multipurpose Reagent for Hydrolysis and Reductive Iodination of Ketals, Acetals, Ketones, and Aldehydes

Article abstract of DOI:10.1021/jo00296a068

The reaction patterns of diiodosilane (SiH2I2, DIS) with ketals, acetals, ketones, and aldehydes were explored.The reagent may be used for mild cleavage of ketals and acetals either hydrolytically to give the parent carbonyl functionality or reductively to produce the corresponding alkyl iodide.At low temperatures (-42 deg C) and short reaction times (few minutes), catalytic amounts (5-10 molpercent) of DIS provide clean deprotection of various ketals and acetals to yield ketones and aldehydes, with no apparent reduction of the latter.At temperatures above 0 deg C, DIS effectively reduces ketals and acetals to iodoalkanes.This reduction is quite general both with respect to ketals and acetals and unprotected ketones and aldehydes.Reaction rates, however, are strikingly dependent on the substrate, with the following tendencies: (a) aromatic functionalities are generally reduced much faster than their aliphatic analogues; (b) ketals and acetals are rapidly reduced to the corresponding iodoalkanes, while free aldehydes, and particularly ketones, are essentially inert under the reaction conditions (but can be significantly activated by catalytic amounts of iodine); (c) dimethyl ketals form the parent ketones preferentially, while all other ketals, including diethyl ketals and dioxolanes, are reduced to iodoalkanes.