Enantioselective allyl coupling

Treatment of the (—)-menthone-derived 2/7-1,3-benzoxazin-4(3//)-one 202 with triflic anhydride gave the triflate 203 in quantitative yield. Palladium-catalyzed cross-coupling of 203 with 2-pyridylzinc halide resulted in formation of an approximately 3 1 mixture of the 4-(2-pyridyl)-2//-l,3-benzoxazine 204 and a 4-imino-l,3-benzodioxane derivative 205 (Scheme 36). Compound 205 was formed by the isomerization of 203, which occurred with complete retention of stereochemistry. The 4-(2-pyridyl)-l,3-benzoxazine derivative 204 was applied in enantioselective allylic alkylations of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate as a chiral ligand inducing a 62% ee in the product <2005JOM(690)2027>. 

In 1998, Yamamoto et al. reported the first catalytic enantioselective allylation of imines with allyltributylstannane in the presence of a chiral 7i-allylpalladium complex 23 (Scheme 9) [15]. The imines derived from aromatic aldehydes underwent the allylation with high ee values. Unfortunately, the allylation reaction of aliphatic imines resulted in modest enantioselectivities. They proposed that a bis-Jt-allylpalladium complex is a reactive intermediate for the allylation and reacts with imines as a nucleophile. The bis-Jt-allylpalladium complex seemed the most likely candidate for the Stille coupling [16]. Indeed, the Stille coupling reaction takes place in the presence of triphenylphosphine even if imines are present, whereas the allylation of imines occurs in the absence of the phosphine [17]. They suggested the phosphine ligand played a key role in controlling the... 

A related rhodium catalyzed enantioselective reductive coupling of acetylene to N arylsulfonyl imines leads to the formation of (Z) dienyl allylic amines (Scheme 1.28) [105]. The scope of the reaction is comparable to that demonstrated for the analogous iridium catalyzed process. The reaction between the acetylene and rhodium leads to the oxidative dimerization of acetylene to form a cationic rhoda cyclopentadiene that then reacts with the imine to generate the product after the protolytic cleavage and reductive elimination. 

Homillos V, P6rez M, Fananas-Mastral M, Feringa BL (2013) Copper-catalyzed enantioselective allyl-allyl cross-coupling. J Am Chem Soc 135 2140-2143... 

Hojoh K, Shido Y, Ohmiya H, Sawamura M (2014) Construction of quaternary stereogenic carbon centers through copper-catalyzed enantioselective allylic cross-coupling with alkylboranes. Angew Chem Int Ed 53 4954-4958... 

Scheme 11.7 NHC-Cu-catalyzed diastereoselective borocupration/nucleophilic attack on carbonyl (left) and enantioselective borocupration/allylic coupling (right).

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