Stannanes organo

The most important palladium-catalyzed processes include Heck vinylation of halides and sulfonates and various cross-coupling reactions in which a nucleophilic intermediate (stannane, organo-zinc halide or boronic acid) is coupled with an electrophile (halide or sulfonate). These coupling reactions are usually restricted to arylation and vinylation because of the tendency of alkylpalladium species to undergo elimination. The pyrrole and indole rings can participate in cross-coupling as either the nucleophilic or electrophilic component. 

Synthesis of aryl ketones or aldehydes from aryl tnllates or iodides and organo stannanes in ihe presence of CO and a palladum catalyst... 

Displacement of the chlorine atom in 395 by sodium thiomethoxide or other mercaptans was reported recently. The same authors also described an efficient synthesis of 4-arylidene-2-phenyl-5(477)-oxazolones 399 from 395 and organo-stannanes via palladium catalyzed Stille reaction (Scheme 7.128). Selected examples are shown in Table 7.36 (Fig. 7.47). 

Ito, Y. Matsuura, T. Murakami, M. N-Substituted organo(silyliminomethyl)stannanes synthetic equivalent to organosilyl carbonyl anion and carbonyl dianion. J. Am. Chem. Soc. 1987, 109, 7888-7890. 

The alkyne is transformed into the corresponding organotin reagent by radical hydrostannylation. First under kinetic control the Z-organo-stannane is formed. But in the presence of excess tributyltinhydride, reversible addition of the tributyltinradical to either carbon atom of the double bond equilibrates the Z-isomer to the more stable -organo-stannane, which is obtained in 53 % (2 steps). TBS- deprotection furnishes 23 (building block II) in 63 % yield. When hydrostannylation and deprotection are carried out the other way round, the yield of this sequence from 20 to 23 drops from 33 % to 29 %. 

Organo-silanes and -stannanes possessing sp caibon-metal bonds also add to carbonyls in the presence of Lewis acids. Alkynylation with silyl- and stannyl-alkynes is promoted by AlCb or Z11CI2 (equations 9 and lO). " Notably, the reaction of l,3-bis(trimethylsilyl)-l-prcq>yne with chloral affords ynic alcohol instead of allenylic alcohol, showing the preferential cleavage of sp C—Si bonds (equation 11). ... 

Other organo-silanes and -stannanes are relatively inert, and addition reactions to aldehydes or ketones have been quite limited. However, there seems to be no reason why these organometals should not find applications in the future through the development of appropriate promoters. Actually, several examples appear in the literature. Aryl- or vinyl-silanes, which possess sp C—Si bonds, add to chloral in the presence of AICI3 (Scheme 2). The intramolecular addition reactions of alkylstannanes to ketones proceed with TiCU (equations 13 and 14). ... 

Lewis acid promoted ring opening of oxiranes with organo-silanes or -stannanes is reported. TMS-CN cleaves the C—O bond in the presence of AlCh, Et2AlCl, Ti(OPr )4 or LnXs, and P-hydroxy-... 

Table 4.1 Rates of the reaction of some carbon-centred radicals with organo-stannanes.15...

Because the initial oxidative addition of Pd(0) is faster with the aryl bromide than the vinyl bromide, the vinyl groups can be selectively coupled to give 78, by using one equivalent of organo-stannane or boronic acid. Coupling with a second equivalent of organo-... 

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