Coupling allylic

For a review of some allylic coupling reactions, see Magid, R.M. Tetrahedron, 1980, 36, 1901. 

H n.m.r.spectrum of compound 64 showed the well-known allylic coupling 111 between the protons on C-4 and C-6 and C-4 and C-6. On reacting with silver fluoride and pyridine, 2,3,4,l, 3, 4 -hexa-0-acetyl-6,6 -dibromo-6,6 -dideoxysucrose, like the 6,6 -diiodo derivative (63), gave the corresponding 6,6 -dideoxy-5,5 -diene derivative.96... 

The magnitude of the long-range allylic coupling, (V ) is controlled by the dihedral angle between the C-H bond and the plane of the double bond in a relationship reminiscent of the Karplus relation. 

Homoallylic coupling (5,/nn) is closely related to allylic coupling in its stereochemical dependence. In cyclic compounds the existence of homoallylic couplings can be used for configurational assignments. For example, tru s-2,5-disubstituted bislactim ethers show a 4 Hz difference in the couplings between H-2 and H-5200. 

SCHEME 62. Synthesis of hennoxazole A via Pd-catalyzed alkenyl-allyl coupling... 

An alternative allylic coupling has been reported (J. Am. Chem. Soc. 2004,126, 10676 and 11130) by Amir Hoveda of Boston College. Coupling of the allylic phosphonate 8 with diethyl zinc in the presence of an enantiomerically-pure Cu catalyst gives the branched product 9 in 95% . It is striking that the reaction works almost as well with the allylic phosphonate 10. Reaction with diethyl zinc in the presence of the enantiomerically-pure Cu catalyst forms the quaternary center ofl 1 in 91 % . 

For a review of some allylic coupling reactions, see Magid Tetrahedron 1980, 36, 1901-1930, pp. 1910-1924, "In this section are discussed methods in which one molecule is a halide. For other allylic coupling reactions, see 0-87, 0-90, and 0-91. 

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