Vinyl-N-heterocyclics

Bis(pyrazolyl)borate copper complex 902 has been employed as a catalyst in homogeneous and heterogeneous styrene epoxidation reactions <2000CC1653>. Pyrazole palladacycles 903 have proved to be stable and efficient catalysts for Heck vinylations of aryl iodides <2000CG2053>. A hemilabile pyrazolyl-functionalized N-heterocyclic carbene complex of palladium(ll) such as 904 has been found to be an excellent catalyst for Heck and Suzuki crosscoupling reactions in ionic liquids <2006JOC426>. 

NMR experiments on the reactions of halophosphates esters with pyridine showed that equilibria involving the formation of pyridinium salts in these reactions are almost entirely shifted to the left for chloro- and bromo-phosphates and to the right for the corresponding iodophosphates. This explains dramatic differences in chemical reactivity between these compounds. Substituted medium-sized and large N-heterocycles (117) have been prepared via an extension of the Suzuki reaction involving the palladium-catalysed coupling of vinyl-phosphates (118) with aryl or heteroaryl boronic acids (Scheme 27). ... 

Substltuted thiophenes (not readily available, since both electrophilic substitution and metallatlon take place at position 2) can be prepared from the readily avallablg 3-bromothlophene by Pd(0Ac)2-catalyzed reaction with allyllc alcohols. This process has be n extended to the preparation of 3-alkyIpyridines from 3-bromopyrldine, as well as a variety of vinyl-substituted heterocycles from the corresponding bromo precursors. 

N-Heterocyclic carbenes (NHC) are examples of ligands that possess the desired attributes [19]. In 2004, Caddick and Cloke reported that a Pd/NHC-based catalyst cross-couples primary alkyl bromides with alkyl- and vinyl-9-BBN reagents (Eq. 6) [20]. A system composed of Pd(dba)2/IPr HCl/AgOTf (IPr HCl=l,3-bis(2,6-diisopropylphenyl)imidazolium chloride) in the presence of KOt-Bu provides the most efficient catalyst. The yields of the cross-coupling products are modest (Table 3). 

Table 9.5 Copper/ligand catalyzed coupling between vinyl bromides and N-heterocycles.

Mercuric acetate sulfuric acid (N-Vinyl)oxo- from silyloxy-N-heterocyclics... 

Coniugate additions to vinyl-substituted aromatic N-heterocycles 12SL1590. 

Silyl enol ethers of P-amido substituted cyclohexanone give [2+2] cyclisadons to form N-heterocycles, fluoroalkyl amides convert cyclohexanones to the enol ether, C N02)4 witii benzocyclohexanone gives a-nitroketones, and with diazoesters give optically active siloxycyclopropanes. Pb(OAc)4 gives acetoxy derivatives, deracemisation by enantioselective protonation demonstrated, methyl vinyl ketones added to give a,e-diones, and... 

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