Ditin reagent

Palladium-catalyzed intramolecular cross-coupling reaction of bis-aryl halides using ditin reagents. 

Ollivier and Renaud built on his new ditin-mediated radical azidation with benzenesulfonyl azide [125] to introduce tandem intramolecular cyclization-azidation processes [126]. For example, iodoacetal 131 provides the corresponding tertiary azide 132 in high yield as a 3 2 mixture of endolexo diastereoisomers (Scheme 41). The necessify of using ditin reagents still constitutes a drawback in this method, as DLP-mediated tin-free reaction conditions failed due to an inefficient chain process. 

Supported Ditin Reagents. Ditin reagents can be obtained by reduction of organotin halides with arene metal radical anions or by dehydrogenation of supported organotin hydrides in the presence of Pd(PPh3)4 (Scheme 5.5.13) ... 

Using supported ditin compounds, it is possible to promote free radical addition of organic iodides to ttiple bonds and atom transfer cyclization of e-unsaturated iodoacetates or iodoamides using UV irradiation. In this latter case, tin contamination was found to be 5-34 ppm using 0.1 eq. of ditin reagent, and recycling of the tin reagent was also possible. 

Lithium metal in tetrahydrofuran can also be used as the coupling reagent, and unsymmetrical ditins can be prepared when the reaction is conducted in stages (162,163). 

Treatment of halides and triflates with ditin and palladium catalyst is quite useful, especially for the preparation of the corresponding tin reagents with sensitive functionalities (Scheme 52) [16,218]. 

Although hexabutyl ditin is readily separated from even moderately polar allylic stannanes by column chromatography, when the allylic tin reagents are nonpolar, removal is often not possible. Frequently small amounts of distannane impurity can be carried on to the addition reaction without an adverse affect on the yield. As the products of the additions are alcohols, subsequent removal of the distannane poses little problem. 

The lithium reagents may be used to make unsymmetrical ditin compounds (220) just as the sodium reagents, thus avoiding the use of liquid ammonia. 

Reaction with alcoholic silver nitrate has been used as a qualitative test for the ditin linkage, and a variety of compounds, including aryl derivatives, have been shown to deposit a silver mirror on treatment with the reagent (195, 198, 200, 215, 244). Potassium permanganate is also reduced readily (200,265). Hexaphenylditin has been shown to react virtually quantitatively to produce triphenyltin hydroxide when subjected to the action of potassium permanganate in acetone solution (265). 

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