Copper-based catalysts alkylations

This methodology was applied to a concise synthesis of the alkaloid epilupinine (Scheme 18.10) [27]. N-alkylation of proline benzyl ester with bromo diazoketone 25 gave substrate 26. Treatment with either Rh2(OAc)4 or various copper-based catalysts... 

A majority of the literature on ATRP focuses on the synthesis of styrene and its derivatives with copper-based catalysts. One of the most extensively studied systems is the polymerization of styrene conducted with CuBr, nitrogen-based ligands, and alkyl bromides as initiator. Better molecular weight control is obtained at low temperatures, presumably due to a lower contribution of thermal self-initiation during the early stage of the polymerization. For example, the reaction temperature can be lowered to 80-90 °C when efficient catalysts, such as CuBr/PMDETA, are used [19-22, 30]. 

Another efficient method to obtain metal carbenoid species is by treating diazo compounds with catalytic amounts of transition metals (see preceding two papers) [22, 23, 24]. Although a-diazo carbonyl compounds [23] are very useful precursors for this transformation, alkyl- or aryl-substituted diazo compounds can be also used [24,25]. The most effective catalysts for this reaction are rhodium and copper based, but several other transition metals, possessing a vacant... 

An alternative approach to aziridine synthesis involves transfer of a carbenoid species to imines. Jacobsen achieved the first asymmetric aziridination of imines by transfer of copper carbenoids derived from copper bis-oxazohne catalysts and ethyl diazoacetate onto imines, but this process only proceeds with moderate yield and selectivity. Better results have been achieved by addition of ethyl diazoacetate to imines in the presence of enantiopure Lewis acids such as the boron-based catalysts prepared from vaulted biaryls such as VAPOL (4.154) and B(OPh)3. A range of aryl and alkyl N-benzylaldimines, for example (4.155) and (4.156), undergo aziridination to give ds-aziridines with high ee using this procedure. 

In 1959, Osbond and cowoikers synthesized arachidonic acid (8) based on iterative use of propargyl alcohol [41]. This synthetic protocol is considered as a general route to synthesize methylene-interrupted PUFAs (Scheme 3.9) [42]. Copper promoted acetylide alkylation of propargyl alcohol (36) with propargylic bromide 35 afforded diyne 37 after bromination of the resulting alcohol. Two more sequences of copper promoted alkylation gave tetrayne 40, which was reduced with Lindlar s catalyst to give arachidonic acid (8). 

The use of copper catalysts based on chiral phosphorus ligands to assist 1,4-additions of dialkylzinc reagents has in recent years produced major breakthroughs, with excellent enantioselectivities. A number of monodentate and bidentate phos-phoramidites, phosphites, phosphonites, and phosphines are now available as chiral ligands for alkyl transfer to a variety of cyclic and acyclic enones. So far. 

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