Copper-based allylation reagents

One approach that was influential in our research on the synthesis and applications of allylboronates to access a-methylene y-lactones, which was reported by Sidduri and Knochel, utilize a mixed zinc copper reagent that allowed for the one-pot preparation of a-methylene y-lactones (Equation 10). The desired copper-based allylation reagents are formed with high selectivity through a cfs-carbocupration, and the diastereoselectivity of aldehyde addition is high, which suggests a Type I chair-Uke transition state similar to allylboration reactions (see Section 5.1). 

Typical Experimental Details of Copper Chemistry 233 Table 5.14 1,4-Conjugate additions with copper anion-based allyl organocopper reagents. 

This type of chemoselectivity has been observed in the oxidations of alcohols using copper(II) chloride and a catalytic quantity of 2,2,6,6-tetramethylpiperidinyl-l-oxyl (11 equation 11). The oxidizing species which is generated, in fw example the oxidation of (12) to (13), is the cation (14), which may also be produced using electrochemicai oxidation (in the wesence of the weak base 2,6-lutidine). Allylic and ben lic alccAols are easily oxidized by this reagent, whereas secondary alcdiols react slowly. 

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