Phosphine ligands cychzation

The Shibasaki cychzation of mc.vo-cyclohexa-1,4-dienes in the presence of a chiral palladium complex and silver carbonate in l-methyl-2-pyrrolidinone is probably the first example of an enantioselective Heck reaction (Scheme 10.34).60 The enantiomeric excess could be slightly improved by replacing the chiral phosphine ligand BINAP with the corresponding less coordinating arsine ligand, as well as replacing silver carbonate with silver phosphate.61,62... 

Total synthesis of (—)-macrolactin A, a 24-membered macrolide, was achieved based on intramolecular coupling of alkenylstaimane with iodide in 64 to afford the macrolide 65 as a key reaction. The cychzation occurred without a phosphine ligand in NMP in 42% yield [32],... 

Intramolecular cross-coupling of prochiral inflate 61a, which contains a pair of enan-tiotopic alkylboranes and is generated by hydroboration of prochiral diene 60a, was examined with palladium catalysts coordinated with several chiral phosphine ligands (Scheme Highest enantioselectivity in forming cyclopentane derivative (R)-62 of 28% ee was observed with ferrocenylbisphosphine 63. In the cychzation of 60b, which has a quaternary carbon center, the enantioselectivity was a httle higher, PPFA (5) giving 62b of 31% ee. 

The use of Cp rings with pendant phosphines in CpCoL2 complexes has also been reviewed. Carbonyl complexes of this type (Cp Co(CO)2) lose CO at room temperature to afford pendant phosphane adducts (equation 46). The chelated phosphane can then be uncoordinated with ligands such as cod substitution of cod (Section 5.1.4) with alkynes allows the cobalt complex to participate in cychzation reactions (Scheme 26). 

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