Metathesis nucleophilic addition

Cassidy JH, Marsden SP, Stemp G. Stereoselective synthesis of 2,3,5-trisubstituted tetrahydrofurans by an allyl silane metathesis-nucleophilic addition sequence. Synlett 1997 1411-1413. 

Stereoselective, conjngate allylation of more remote positions nsing aUyl trimethylsilane and TiCU is possible. Further transformation by nucleophilic addition and ringclosing metathesis affords fused polycychc ring systems (Scheme 88). Stabilized anions and organocopper see Copper OrganometaUic Chemistry) reagents also participate in Michael-type additions to complexed Q, /3-unsaturated aromatic enones. 

Metallacyclic complexes play an important role as reactive intermediates in catalytic cycles initiated by homogeneous transition-metal complexes. Thus, metallacyclobutanes are discussed as intermediates in alkene metathesis, isomerization of strained cyclopropane compounds and many other reactions. On the other hand, numerous examples of isolable me-tallacyclobutane complexes have been reported. These can be formed by different routes such as carbon-carbon bond cleavage of cyclopropane compounds (A), cyclometallation via C — H bond cleavage (B), nucleophilic addition to allyl complexes (C), rearrangement of metallacyc-lopentanes (D) or transmetalation of 1,3-dimetallalated carbon chains (E). ... 

In addition to ring-closing metathesis, nucleophilic aromatic substitution and Heck coupling reactions can also be used to efficiently form cyclic peptides using microwave irradiation. 

Natural product synthesis as a test of newly developed methodologies, for example, partial reduction of furans and pyrroles, nucleophilic addition to pyridinium salts. Os-catalyzed oxidative cyclization for the synthesis of tet-rahydrofurans and pyrrolidines, tethered aminohydroxylation of aUcenes, and ring-closing- and cross-metathesis for the constmction of heteroaromatics 12CC11924. 

The four most common methods for the synthesis of late transition metal enolates are oxidative addition to halocarbonyl compoxmds, ligand metathesis with main group enolates or silyl enol ethers, nucleophilic addition of anionic metal complexes to halocarbonyl electrophiles, and insertion of an a,3-imsaturated carbonyl compoimd into a metal hydride. Examples of these synthetic routes are shown in Equation 3.47-Equation 3.50. Equation 3.47 shows the synthesis of a palladium enolate complex by oxidative addition of ClCHjC(0)CHj to Pd(PPh3), Equation 3.48 shows the synthesis of a palladium enolate complex by the addition of a potassium enolate to an aryl Pd(II) halide complex, and Equation 3.49 shows the synthesis of the C-bound W(II) enolate complex in Figure 3.7 by the addition of Na[( n -C5R5)(CO)jW] to the a-halocarbonyl compound. Finally, Equation 3.50 shows the synthesis of a rhodium enolate complex by insertion of but-l-en-3-one into a rhodium hydride. This last route has also been used to prepare enolates as intermediates in reductive aldol processes. - ... 

In contrast to many other methods commonly employed for stereoselective alkene synthesis such as elimination, alkenylation, alkene metathesis, alkyne addition, the JuUa olefination, and the Peterson olefination [1-3], the olefination reactions of phosphorus-stabilized carbon nucleophiles remain very powerful for modem stereoselective alkene synthesis owing to their convenience, complete positional selectivity, and generally high levels of geometrical control. However, further modifications of these olefination reactions are definitely needed to broaden substrate scope, enhance stereoselectivity, and improve environmental impacts. 

SnCU is also the principal source for alkyltin chlorides, RnSnCU-n- Allyltrialkyltin reagents react with SnCU to produce allyltrichlorotin species through an Se2 pathway (eq 1). Silyl enol ethers react with SnCU to give a-trichlorotin ketones (eq 2). Transmetalation or metathesis reactions of this type are competing pathways to nucleophilic addition reactions where SnCU is present as an external Lewis acid. As a consequence, four important experimental variables must be considered when using SnCU as a promoter (1) the stoichiometry between the substrate and the Lewis acid (2) the reaction temperatnre (3) the nature of the Lewis base site(s) in the substrate and (4) the order of addition. These variables influence the reaction pathway and product distribution. ... 

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