Organotin reagents coupling

Coupling of Enol Triflates with Organotin Reagents. Coupling of an enol triflate with (Z)-1 -propenyltri-n-butyltin proceeds smoothly using Pd2(dba>3 as a catalyst in the absence of a phosphine ligand (eq 5). ... 

The ester 870 is prepared by the cross-coupling of the chloroformate 869 with an organotin reagent. Some chloroformates are easily decomposed by a Pd catalyst, and hence the reaction should be carried out by slow addition of the chloroformates. Similarly, the amide 872 is prepared by the reaction of the carbamoyl chloride 871 [742]. The coupling of alkylcopper with ethyl chloroformate catalyzed by Pd affords esters[743]. 

In the direct coupling reaction (Scheme 30), it is presumed that a coordinatively unsaturated 14-electron palladium(o) complex such as bis(triphenylphosphine)palladium(o) serves as the catalytically active species. An oxidative addition of the organic electrophile, RX, to the palladium catalyst generates a 16-electron palladium(n) complex A, which then participates in a transmetalation with the organotin reagent (see A—>B). After facile trans- cis isomerization (see B— C), a reductive elimination releases the primary organic product D and regenerates the catalytically active palladium ) complex. 

Stannyl derivatives of 2ff-pyran-2-one, accessible from bromopyranones by cross coupling with organotin reagents, themselves take part in Pd(0)-catalyscd cross coupling with enol triflates. This methodology offers a new approach to steroidal pyran-2-ones <96JOC6693>. 

Compared to the previously described transition metal-catalyzed transformations in this chapter, microwave-assisted Stille reactions [74] involving organotin reagents as coupling partners are comparatively rare. A few examples describing both inter- and intramolecular Stille reactions in heterocyclic systems are summarized in Scheme 6.38 [47, 75-77]. Additional examples involving fluorous Stille reactions are described in Section 7.3. 

Halogenated pyrroles can serve as the aryl halide in Stille couplings with organotin reagents. Scott has used this idea to prepare a series of 3-vinylpyrroles, which are important building blocks for the synthesis of vinyl-porphyrins, bile pigments, and indoles [77]. Although 3-chloro-and 3-bromopyrroles fail completely or fared poorly in this chemistry, 3-iodopyrroles 101 work extremely well to yield 3-vinylpyrroles 102. 

One of the first cross-coupling reactions performed on solid supports was the Stille reaction [250] which is a paUadium-catalyzed reaction of a trialkylaryl or trialkylalkenyl stannane with an aromatic iodide, bromide or triflate. In contrast to the process in liquid-phase, the organotin reagent is easily removed from the solid-phase because of the subsequent washing processes. Immobilized aryl halides have been frequently coupled with aryl and alkenylstannanes, whereas stan-nanes attached to the solid support have been used less frequently for the StiUe reaction. An example is the synthesis of a benzodiazepine library by EUman et al. Recently, a Stille cross-couphng reaction has been employed in the synthesis of al-kenyldiarylmethanes (ADAM) series of non-nucleoside HlV-1 Reverse Transcriptase Inhibitors (Scheme 3.14) [251]. 

Samuelsson, L. Langstrom, B. J. Labelled Comd. Radiopharm. 2003, 46, 263. MitcheU, T. N. Organotin Reagents in Cross-Coupling Reactions. In Metal-Catalyzed Cross-Coupling Reactions (2nd edn) De Meijere, A. Diederich, F. eds., 2004, 1, 125-161. WUey-VCH Weinheim, Germany. (Review). 

Reaction with Organotin Reagents (Migita-Kosugi-Stille Coupling) 656... 

Palladium-Catalyzed Coupling of Acid Chlorides with Organotin Reagents (E)-Ethyl-4-(4-n1trophenyl)-4-oxo-2-butenoate A, F. Renaldo, J, W. Labadie, and J. K. Stille, Department of Chemistry, Colorado State University, Ft. Collins, CO 80523... 

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