A varity of synthetic uses of iodotrichlorosilane reagent in some organic reactions

Iodotrichlorosilane is readily available by mixing cheap , commercially available tetrachlorosilane with sodium iodide . Halogen analysis of the distillate indicates that the exchange of iodide ion practically stops at the first stage and yields iodotrichlorosilane under these conditions . for experimental purposes this mixure may be used in place of the isolated ITCS .

1-The generation of carbonyl compounds from acetals and ketals

The generation of carbonyl compounds from gem-diethers is an important process that is of continuing interest. Transacetalisation and hydrolysis with awide variety of acid catalysts are the traditional methods of choice . iodotrichlorosilane can be used for the high yield cleavage of acyclic ketals , but is unsuitable for cyclic ketals whilst diiodosilane may be used at low temperatures but above zero it produces iodoalkanes.

We now report that ITCS readily cleavages both cyclic and acyclic acetals and ketals at room temperature .

The reactions with acetals are very fast as , even though ITCS readily cleavage esters and phenolic methyl ethers

Two equivalent of ITCS are required for efficient production of the carbonyl compounds .when one equivalent of ITCS is used , then a α-iodoethers can be isolated

2-Uses of reductive properities of iodotrichlorosilane

2.1-Chemoselective reduction of alpha,beta unsaturated ketones and nitriles

A tetrachlorosilane-sodium iodide has been applied to many organic synthesis as an iodotrichlorosilane (ITCS) equivalent , where beside the application to cleavage of ethers ; esters ,acetals and ketals, it can be used to introduce an acetamide or benzamide group into aromatic or aliphatic aldhydes to produce corresponding derivative containing anitrogen function in the place of the oxygen function of its carbonyl group

Example: by using two equivalent of iodotrichlorosilane , β-phenyl α,β-unsaturated ketone can be reduced to the corresponding saturated ketones in high yield at room temp in acetonitrile solvent

R: phenyl

The suggested mechanism of this reaction involves 1,4 addition of iodotrichlorosilaneto enone to produce β-iodosilylenol ether intermediate where β-iodo ketons can be isolated after hydrolysis ,the intermediate is attacked by another molecule of ITCS to give another intermediate which have hydrogenated product by hydrolysis

2.2- with some natural products

The versatility of iodotrichlorosilane (ITCS) ,(SiCl4/NaI in situ) as auseful reagent in organic synthesis is well established

Attempting to introduce an acetamide group in danthron to produce an anthracene derivative containing a nitrogen function in the place of the oxygen function of its carbonyl group, we found that by using five equivalents of ITCS in presence of CH3CN and CH2Cl2 the resulting product was anthralin

Since the main objective of the study is to establish the proposing mechanism of the reaction , it will be convenient to mention firstly some of the facts concerning the reaction under investigation these facts are :

1-by using 3 moles of ITCS with danthron under the same conditions ,the reaction does not proceed

2-under the same conditions the reaction of anthraquinone with five equivalent of ITCS does not proceed to reduce the carbonyl group

3- the reaction of carbonyl conjugated with an aromatic ring was found to be effected with some selectivity in the presence of hydroxyl substituents in the ring . so , the order reactivity of carbonyl groups at C-9 and C-10 are not the same . the carbonyl at C-9 is less reactive for the reaction owing to unfavour electronic factor and more sterically hindered .

Therefore, the suggested mechanism may proceed as follow: in the scheme danthrone reacts with 3 equivalents of ITCS to give intermediate (1) and two equivalents of HI . the α-iodosilyl ether (intermediate could be reduced by trichlorosilyl hydride ,which was produced by the reaction of ITCS with the liberated HI , to give intermediate (2) which could react with H2O during work up to give the product .

The mechanism of the reaction shows that , one mole of danthrone needs 5 equivalents of ITCS to be reduced to anthralin