Vinyl halides synthesis

Palladium(0)-Catalyzed Reaction of 1-Alkenylboronates with Vinylic Halides Synthesis of (lZ,3E)-l-Phenyl-l,3-octadiene... 

Reaction with Vinylic Halide. Synthesis of Conjugated Alkadienes... 

SENARY Conjugated Aldehyde Synthesis Formation ot polyunsaturated aldehydes trom vinyl halides and enamlnoaldehydes... 

Oleno synthesis via Pd catalyzed vinyl coupling o( vinyl borates with vinyl halides... 

Unsymmetrical trans vinyl halides have been prepared from acetylenic alcohols by Corey and co-workers (as illustrated in the accompanying formulation) in connection with their synthesis of farnesol and Gecropia juvenile hormone. Several syntheses of vinyl halides (with... 

The original Sonogashira reaction uses copper(l) iodide as a co-catalyst, which converts the alkyne in situ into a copper acetylide. In a subsequent transmeta-lation reaction, the copper is replaced by the palladium complex. The reaction mechanism, with respect to the catalytic cycle, largely corresponds to the Heck reaction.Besides the usual aryl and vinyl halides, i.e. bromides and iodides, trifluoromethanesulfonates (triflates) may be employed. The Sonogashira reaction is well-suited for the synthesis of unsymmetrical bis-2xy ethynes, e.g. 23, which can be prepared as outlined in the following scheme, in a one-pot reaction by applying the so-called sila-Sonogashira reaction ... 

This organometallic coupling reaction is useful in organic synthesis because it forms carbon-carbon bonds, thereby making possible the preparation of larger molecules from smaller ones. As the following examples indicate, the coupling reaction can be carried out on aryl and vinylic halides as well as on alkyl halides. 

For reviews of organotin hydrides, see Neumann, W.R Synthesis, 1987,665 Kuivila, H.G. Synthesis, 1970,499, Acc. Chem. Res., 1968,1,299. Tributyltin hydride also reduces vinyl halides in the prescence of a palladium catalyst. See Uenishi, J. Kawahama, R. Shiga, Y Yonemitsu, O. Tsuji, J. Tetrahedron Lett., 1996, 37, 6759. 

The DPE reduction is used as a test reaction to characterize the materials and optimize the preparation conditions of the catalyst. Since hydroaluminations can also be used for the synthesis of carboxylic acids, deuterated products, or vinyl halides via quenching with CO2, D2O or Br2 [44], the method is also a valuable organic synthesis tool. However, as compared with molecular catalysts like Cp2TiCl2 that are known to catalyze hydroaluminations [44], the titanium nitride materials described here are solid catalysts and can be separated by centrifugation. Moreover, they can be reused several times, which is an advantage as compared to molecular catalysts. 

In recent years, cross-coupling methodology has emerged as a viable tool for enamide synthesis, and, indeed, there are a number of published protocols which employ palladium- or copper-catalyzed stereospecific amidations of vinyl halides [17]. For example, Buchwald and coworkers had recently shown that a copper-catalyzed cross-coupling of vinyl bromides or iodides proceeded with retention of stereochemistry (Scheme 9.16), though the only example using a tetrasubstituted vinyl halide, 23, lacked the need for any stereochemical control in the halide portion [18]. Based on this it seemed feasible that the desired enamide 22 could potentially be assembled via a comparable coupling between amide 24 and a stere-odefined vinyl halide such as 25. 

Unfortunately, it quickly became apparent that a shortfall in this proposal was an inability to prepare the desired vinyl halide 25 in a straightforward and selective manner [19]. In contrast, we reasoned that the selective formation of an enol sulfonate, such as the enol triflate 26a, could be controlled by judicious tuning of enolization conditions starting from the corresponding ketone, and that such an enol sulfonate would possibly be a substrate for a palladium-mediated coupling (Scheme 9.17). In this way a common intermediate from the previously defined synthesis, that is, the racemic ketone rac-13 or its cyano equivalent rac-5 could be used to generate the required enamide. 

A wide variety of other functional groups can be employed in these annulations. For example, this chemistry has been extended to the synthesis of 1,2-dihydroisoquinolines, benzofurans and benzopyrans (Scheme 3).3 One can also employ vinylic halides and triflates in this process.4... 

A similar approach was used by the Alcaide group [183] in the synthesis of tricyclic (3-lactams 6/1-391 from 6/1-390 (Scheme 6/1.99). In this domino process the primarily obtained it-allyl-Pd-complex reacts with the N-nucleophile of the urethane moiety to form a C-N-bond and a vinyl halide. The final step is then an intramolecular Heck-type reaction of the vinyl halide with the alkyne moiety and re-... 

In the course of our successful synthesis, we identified several limitations of our new method and associated strategy (1) the harsh conditions of the bicyclization reaction do not tolerate base-sensitive functionality such as vinyl halides (2) post-cyclization manipulations such as iododesilylation reactions are complicated by the sensitive/ reactive functionality of the products (a,p-unsaturated aldehyde, indoline, etc.) and (3) the incorporation of the required functionality into the Zincke aldehyde requires the synthesis of a complex tryptamine derivative, resulting in a lengthy, non-convergent route. In order to develop a concise route to strychnine, we would have to address each of these issues, and a straightforward solution to obviate all of these is described below. 

Suitably positioned vinyl halide can undergo Heck-type intramolecular coupling to generate dienes (equations 124 and 125)216,217. When one of the reacting partners in the Heck reaction is a diene, trienes are obtained (equation 126)218. Heck coupling of ally lie alcohols and alkenyl iodides has been employed for the synthesis of vitamin A and related compounds (equation 127)219,220. A similar double Heck reaction on a Cio-diiodide with a Cis-allylic alcohol leads to -carotene as a mixture of isomers (equation 128)209e. 

Several examples of transition metal catalysis for the synthesis of piperidines appeared this year. Palladium catalyzed intramolecular urethane cyclization onto an unactivated allylic alcohol was described as the key step in the stereoselective synthesis of the azasugar 1-deoxymannojirimycin . A new synthetic entry into the 2-azabicyclo[3.3.1]nonane framework was accomplished through a palladium mediated intramolecular coupling of amine tethered vinyl halides and ketone enolates in moderate yields . A palladium catalyzed decarboxylative carbonylation of 5-vinyl... 

Veits, Y.A., Karlstedt, N.B., and Beletskaya, I.P, Cross-coupling of silylphos-phines with substituted vinyl halides as a method of 2-alkenylphosphine synthesis, Zh. Org. Khim., 30, 66, 1994. 

Axelrad, G., Laosooksathit, S., and Engel, R., A direct synthesis of vinylic phosphonates from vinylic halides, Synthetic Commun., 10, 933, 1980. 

Na2CC>3), 25 °C, 24 h. Larock extended his work in several ways [302-305], particularly with regard to Pd-catalyzed cross-coupling of o-allylic and o-vinylic anilides with vinyl halides and triflates to produce 2-vinylindoles [303-305], an example of which is shown [305]. The related "Larock indole synthesis" is discussed separately in the next section. 

Isomerization of 1,3-dienes (12, 36).3 The 1,5-hydrogen shift in isomerization of 1,3-dienes catalyzed by (naphthalene)Cr(CO)3 (1) can be used for synthesis of aryl-substituted exocyclic alkenes, which are not readily available by coupling of aryl halides with exocyclic vinyl halides. 

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