Carbonyl groups tolerance

Another feature of the Pd—C bonds is the excellent functional group tolerance. They are inert to many functional groups, except alkenes and alkynes and iodides and bromides attached to sp carbons, and not sensitive to H2O, ROH, and even RCO H. In this sense, they are very different from Grignard reagents, which react with carbonyl groups and are easily protonated. 

It looks as though all that is needed is to prepare the acetylenic anion then alkylate it with methyl iodide (Section 9 6) There is a complication however The carbonyl group m the starting alkyne will neither tolerate the strongly basic conditions required for anion formation nor survive m a solution containing carbanions Acetyhde ions add to carbonyl... 

This method for introduction of the thioether functional group tolerates the presence of a broad range of functional groups, such as alkene, ester, carbonyl, and cyano groups. 

The dehydration of primary amides with hydrosilane catalyzed by iron carbonyl clusters, such as [Et3NH][HFe3(CO)n] and Fe2(CO)9, was achieved by Seller and coworkers in 2009 (Scheme 43) [145]. This reaction shows good functional group tolerance (e.g., such as aromatic, heteroaromatic, and aliphatic substrates). 

The hydrosilylation of carbonyl compounds by EtjSiH catalysed by the copper NHC complexes 65 and 66-67 constitutes a convenient method for the direct synthesis of silyl-protected alcohols (silyl ethers). The catalysts can be generated in situ from the corresponding imidazolium salts, base and CuCl or [Cu(MeCN) ]X", respectively. The catalytic reactions usually occur at room tanperature in THE with very good conversions and exhibit good functional group tolerance. Complex 66, which is more active than 65, allows the reactions to be run under lower silane loadings and is preferred for the hydrosilylation of hindered ketones. The wide scope of application of the copper catalyst [dialkyl-, arylalkyl-ketones, aldehydes (even enoUsable) and esters] is evident from some examples compiled in Table 2.3 [51-53],... 

When the epoxy-isobutenyl ester of crotonic acid is treated with the Cp2ZrCl2/AgC104 Lewis acid, the epoxide is opened by intramolecular assistance of the ester carbonyl group, giving a dioxolenium cation (Scheme 8.49). This species is a highly electrophilic Diels—Alder dienophile that reacts with a range of dienes. THF deactivates cationic zirconocene species and is therefore not tolerated as a solvent [89]. 

Formation of C-C bonds remains the ultimate challenge to the synthetic chemist. The employment of new synthetic methods in complex target synthesis can be frustrated by a lack of functional group tolerance and substrate specificity. These problems can be somewhat alleviated within conjugate addition reactions by the use of secondary amine catalysts where a number of important and highly selective methods have been developed. Two principle classes of nucleophile have been shown to be effective in the iminium ion activated conjugate addition of carbon nucleophiles to a,P-unsaturated carbonyl systems aryl, heteroaromatic and vinyl... 

Gyclization/hydrosilylation of enynes catalyzed by rhodium carbonyl complexes tolerated a number of functional groups, including acetate esters, benzyl ethers, acetals, tosylamides, and allyl- and benzylamines (Table 3, entries 6-14). The reaction of diallyl-2-propynylamine is noteworthy as this transformation displayed high selectivity for cyclization of the enyne moiety rather than the diene moiety (Table 3, entry 9). Rhodium-catalyzed enyne cyclization/hydrosilylation tolerated substitution at the alkyne carbon (Table 3, entry 5) and, in some cases, at both the allylic and terminal alkenyl carbon atoms (Equation (7)). 

Substitution at the terminal position of the allylstannane, as in crotonyltributyl stannane, however, is not tolerated, because hydrogen abstraction from the allylic position is a competing reaction [21], An extension of the method involves the coupling of the anomeric radical precursors 28 with the allyltributyltin reagent 29 [14], In the reagent 29 the double bond is activated toward addition of nucleophilic radicals by the electron-withdrawing t-butoxy carbonyl group. The obtained product 30 has been useful en route to 3-deoxy-D-marmo-2-octulosonic acid (KDO). 

Reaction of the complex 24 with terminal alkene 25 generates styrene and the real catalytic species 27 via the ruthenacyclobutane 26. The complex 24 is commercially available, active without rigorous exclusion of O2 and water, and has functional group tolerance. Carbonyl alkenation is not observed with the catalysts 22 and 24. Their introduction has enormously accelerated the synthetic applications of alkene metathesis [11]. 

The other way to prepare cyclopropanes is based on the spin-center-shift. Thus, aryl-alkyl ketones, 26, bearing a leaving group X adjacent to the excited carbonyl group undergo a smooth cyclization to benzoylcyclopropanes 27 in moderate to good yields (Scheme 6b) [4a, b]. The reaction tolerates a variety of functional groups, often proceeds stereoselectively, and can be extended to the preparation of bicyclo[n.l.O]alkane derivatives. 

A series of CMs of a,/i-unsaturated carbonyl compounds with allylsilanes have been tested in the presence of the Hoveyda-Grubbs catalyst (Eq. 44) [76]. Functionalized allylsilanes have been obtained in moderate-to-good yield and very good stereoselectivity in favour of the E isomer. Examples have proved a high functional group tolerance of the Hoveyda-Grubbs catalyst. 

The reaction tolerated various functional groups, thus allowing the in situ preparation of allylboron compounds possessing a carbonyl group (Equation (32)).236 The tandem diboration-intramolecular allylboration provided a diastereoselective access to the cycloalkanes bearing 1,3-diols. 

---