Allylboronates from Palladium-catalyzed Cross-coupling Reactions with Allyl Electrophiles

6 Allylboronates from Palladium-catalyzed Cross-coupling Reactions with Allyl Electrophiles 

Palladium-catalyzed substitution of an allylic acetate such as 37 with diboronyl reagent 24 gives good yields of allylboronates in DMSO as solvent (Equation 21) [57]. This reaction is a steieoconvergent process the boron tends to add to the least substituted end of unsymmetrical allylic units, and both E and Z isomers of acetate 37 yield the E-isomer of 38. Another drawback to this process is that the product is often formed with variable yields of the allylic dimer (e.g., 39). Allylic halides were also employed as substrates with pinacolborane as the borylating agent and a platinum catalyst [58]. 

Recently, allylic acetates were borylated as the first step of an efficient one-pot procedure for the allylation of aldehydes [59]. Borylation of allylic acetates can also be performed in tandem with an intramolecular allylboration (Section 6.4.1.6). 

A variant of these reactions was optimized based on the Hosomi-Miyaura borylation of a,P-unsaturated carbonyl compounds with nucleophilic boryl copper, providing 2-alkoxycarbonyl (as well as 2-acyl- and 2-cyano) allylboronates such as 40 in high stereoselectivity (Equation 22) [60]. The resulting 2-alkoxycarbonyl reagents react with aldehydes to provide a-methylene-y-butyrolactones. 

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