Heteroatomic nucleophiles oxidation synthesis

Wacker-type reactions are Pd(II)-catalyzed transformations involving heteroatom nucleophiles and alkenes or alkynes as electrophiles [108]. In most of these reactions, the Pd(ll) catalyst is converted to an inactive Pd(0) species in the final step of the process, and use of stoichiometric oxidants is required to effect catalytic turnover. For example, the synthesis of furan 113 from a-allyl-P-diketone 112 is achieved via treatment of the substrates with a catalytic amount of Pd(OAc)2 in the presence of a stoichiometric amount of C uC F [109]. This transformation proceeds via Pd(lt) activation of the alkene to afford 114,... 

The first carbene compound to be well characterized was prepared in 1966 and was one of many Fischer-Type Carbene Complexes io be reported (see equation 7). Fischer carbenes are characterized by heteroatom substituents at the carbene carbon, stabilization by a low-valent metal center, and a partial positive charge at the carbene carbon. In contrast, Schrock Type Carbene Complexes, or alkylidenes, that have alkyl substituents, are found on metal centers in higher oxidation states, and are nucleophilic at carbon. Many Fischer carbenes are known for chromium, whereas chromium alkylidenes are much less common. Monohalocarbenes of chromium, for example, (OC)5Cr=C(F)NEt2, have also been extensively investigated. Two carbene reactions of note for their application to organic synthesis are the cycloaddition of alkenes with carbene complexes and the reaction of aromatic carbenes with alkynes to yield complexed naphthols (the Dotz reaction ). ... 

The two main routes for the synthesis of isoxazoles are (a) the attack of hydroxylamine (NH2OH) on diketones and (b) a reaction of nitrile oxides called a 1,3-dipolar cycloaddition. They thus form a link between the strategy we have been discussing (cyclization of a nucleophile with two heteroatoms and a compound with two electrophilic carbon atoms) and the next strategy—cycloaddition reactions. 

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