Carbonylation Stille coupling

Scheme 31. Catalytic cycle for the Stille reaction carbonylative coupling.

Numerous stannanes have been coupled with halopyridines as electrophiles in the Stille coupling. One of the simplest of these is vinylstannane [82-84]. The Stille reaction of bromopyridine 95 with tributylvinyltin gave angustine (96) [84], an indolopyridine alkaloid. Bromopyridine 95 also took part in a three-component carbonylative-Stille coupling sequence to provide an entry to another indolopyridine alkaloid, naucletine (97) [84]. 

Several other research groups have also made use of 1-iodo glycals in their syntheses of C-l alkyl and aryl glycals (Scheme 8). Vogel and co-workers reported the use of 1-iodo glycals in carbonylative Stille couplings with... 

An alternative route for installing a methyl ketone is the three component carbonylative-Stille coupling with tetramethyltin. An indolopyridine alkaloid, naucletine (58), was prepared using such a sequence from pyridyl bromide 57 <95CC1675>. 

The Stille coupling may be combined with carbonylation in two ways. Acid chlorides may be used as substrates for the reaction with vinyl or aryl stannanes. However, an atmosphere of carbon monoxide is frequently required to prevent decarbonylation after the oxidative addition step. 

Metallated 1-ethoxy-1,3-dienes 697 and 712, obtained from the corresponding acetals by means of the LICKOR base, have been treated with alkyl halides, epoxides, carbonyl compounds, carbon dioxide and carboxylic esters affording ( )-l-substituted 1-ethoxy-1,3-dienes and, after hydrolysis, a,P-unsaturated carbonyl compounds1007-1010 (Scheme 186). Intermediates 697 and 712 have been transformed into the corresponding vinyl stan-nanes, which were submitted to Stille couplings with iodobenzene and benzoyl chloride823. 

The first enantioselective total synhesis of (-)-strychnine was achieved by L.E. Overman and co-workers. The carbon skeleton of the main precursor for the key aza-Cope rearrangementMannich cyclization was assembled by applying a Pd ° -catalyzed carbonylative Stille coupling reaction. Thus, the cyclic vinylstannane was coupled with the triazinone-protected ortho-iodoaniline to afford 80% yield of the aromatic enone using Pd2(dba)3 as the catalyst in the presence of carbon monoxide. 

Jeanneret, V., Meerpoel, L., Vogel, P. C-Glycosides and C-disaccharide precursors through carbonylative Stille coupling reactions. Tetrahedron Lett. 1997, 38, 543-546. 

The reactions have a very wide scope. Acyl halides serve as substrates for Stille couplings in addition to the usual aryl and alkenyl halides however, most alkyl halides cannot be used as substrates. Like Pd-catalyzed carbonylations, reactions proceed most quickly when X = I and rather slowly when X = Cl, although especially bulky phosphine ligands such as /-Bu3P allow even aryl chlorides to undergo coupling at room temperature. Again, triflates are also widely... 

The carbonylative Stille coupling is another extremely useful reaction. When the Stille coupling of Ar-X and R-SnR 3 is carried out under an atmosphere of CO, the product is the ketone (ArCOR). An insertion of CO intervenes between oxidative addition and reductive elimination. 

Problem 6.23. Draw a mechanism for the following carbonylative Stille coupling. 

Ketones can be obtained by coupling of acid chlorides with organostannanes or by carbonylative couplings. The first reaction is one of the older and more general Stille coupling reactionsi i 122 and continues to be used under essentially the original conditions.1 3... 

In addition to the hnear array of pyridyl rings, it was also possible to construct cyclic arrays as in cyclosexipyridine 262 [94], This was accomplished by sequential Stille couplings initiated by reacting 258 with 259 to afford 260. The remaining bromide of 260 was then coupled with a vinyl stannane derivative that produced 261. Unmasking of the latent carbonyl functionality preceded elaboration to 262. 

Enol triflates have emerged as attraetive alternatives to vinyl halides in the Stille coupling partner due to their ease of preparation from readily available carbonyl compounds. The addition of LiCI has been found to be beneficial to Stille enol triflate coupling reactions. Thus, it was not surprising that coupling 5-tributylstannylpyrimidine to enol triflate 134 proceeded in good yield in the presence of LiCI. In this case, the addition of Cul as cocatalysts was found to also be beneficial to the reaction outcome [57]. 

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