Heck reaction elemental reactions

Heck-type arylation reactions of organobismuth compounds were first reported by Asano et al. in 1973 [11]. This article described the stoichiometric reaction of styrene, Ph3E (E = group 15 elements) and Pd(OAc)2 (Scheme 2). Ph3Bi afforded frans-stilbene only in 7% yield. The major product was biphenyl, which was... 

Researchers at Schering Plough were interested in preparing a variety substituted Azetidinones for testing as Cholesterol Absorption Inhibitors. In that sense, the Heck reaction is known to be an effective reaction that provides a useful diversity element and was employed as such. Heck reaction of 5-bromopyridine with chiral the terminal olefin provided the desired product [118]. 

The crucial step of Overman s approach is essentially a Grewe-type disconnection but involves an intramolecular Heck reaction to complete ring B. An enantioselective reduction of 2-allyl-cyclohexeneone 195 introduced a chiral element. Condensation of the resultant S-alcohol, (196) with phenylisocyanate, oxidation of the sidechain olefin with osmium tetroxide and acetonide protection afforded 198, Scheme 22. A copper-... 

Two hypothetical mechanisms have been proposed to explain the Heck reaction on the basis of Pd(II)/Pd(IV) cycles (Scheme 2.12). As discussed in Section 2.2.1, oxidative addition of aryl halides to Pd(II) precursors is both kinetically and thermodynamically difficult. The Pd(II)/Pd(IV) mechanism proposed by Shaw for the Heck reaction (Scheme 2.1) tried to elude this problem by postulating the intermediacy of anionic Pd(II) complexes with increased nucleophilicity, but it is not evident how this mechanism could be adapted to complexes containing PCP or related pincer ligands. With this problem in mind, Jensen [93] made an alternative proposal (Scheme 2.12a), which starts with the oxidative addition ofa C-H bond of the olefin to the Pd(II) pincer complex to afford a Pd(IV) vinyl-hydride intermediate. This idea was inspired by a similar reaction observed with an isostructural Ir(I) PCP complex, but such C-H bond activations are unusual in palladium chemistry. A theoretical analysis by Freeh [63] raled out such possibility, leading instead to the alternative Pd(II)/Pd(IV) cycle depicted in Scheme 2.12b. A key element... 

The general strategy illustrated in Scheme 16.3 is used in the synthesis of indane and tetralin derivatives (Scheme 16.4) [6]. Pd(0)-catalyzed double Heck reaction yielded the hexatriene framework, which on heating underwent disrotatory electrocyclization to yield the dihydroaromatic derivative. Dehydrogenation was carried out either with Pd/C or elemental sulfur to yield the aromatic... 

Siloxane polymers, recently prepared in our laboratories based on the former strategy, are illustrated in Figures 2 and 3 (17). The syntheses were quite efficient Each reaction on the polymer, i.e., hydrosilylation, regiospecific brominadon, and Heck reaction, went to hig conversion, confirmed spectroscopically and by elemental analysis. These were the first reports of the use of phosphonate groups as electron-withdrawing functionalities in NLO-chromophore-containing polymers (17,18). 

Perhaps one of the most challenging aspects of complex molecule synthesis is control of the absolute sense of stereochemistry for the preparation of optically-active compounds. In 1989, Shibasaki and Overman independently reported the first examples of asymmetric Heck reactions. These efforts focused on intramolecular cyclization reactions, which display extra elements of regiocontrol. To date, the asymmetric intramolecular Heck has been exploited in the synthesis of terpenoids, akaloids and polyketides, forging key tertiary and quaternary stereocentres. ... 

The main differences between using an iron cation and Pd(ll) to activate an olefin are (a) Pd(ll) reactions are often catalytic processes (b) the C-Pd a bond that results from nucleophilic attack on the coordinated olefin is reactive and undergoes either decomposition or further transformations, usually with reduction of the Pd species to Pd(0). There are numerous examples of arylation reactions of Pd(ll)-coordinated olefins, but only a few simple alkylation reactions. Pd-catalyzed reactions are usually more important for forming C-X bonds where X is an electronegative element (Section IV). Some examples of typical Pd-catalyzed C-C bond-forming reactions-are given in Eqs.(ll)-(15)(Heck, 1968, 1969), Eq. (16) (Heck, 1972), and Eq. (17) (Brown, 1974) (see also S. Tsuji, 1969 J. Tsuji, 1972 Bird, 1972, Henry, 1973). 

Certain brominated allylic alcohols suffer loss of the elements of HBr when exposed to Heck-t)q)e reaction conditions and so affording the corresponding a, 8-unsaturated aldehydes or ketones (eq 121). ... 

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