A flexible synthetic route to the 16-membered tetramate-embedding macrocyclic scaffold present in various polycyclic tetramate macrolactams (PTMs) was developed which differs from the seminal synthesis of ikarugamycin by Boeckman Jr. in protecting groups and the order of connections. We also devised a short approach to various stereoisomers of the 5/5/6-tricarbocyclic motif found in discodermide and
By a sequence comprising asymmetric hydroboration, boron-zinc exchange, and transmetalation with copper, allylations, alkynylations, and allenylations of unsaturatedketals or acetals can be performed with good enantioselectivities (see scheme, (-)-IpcBH2 =(-)-isopinocampheylborane, TMS=Me3 Si). The products correspond to a formal Michael addition with inversion of polarity.
Synthesis and reaction of secondary and primary diorganozinc reagents using a boron–zinc exchange reaction
作者:Eike Hupe、M.Isabel Calaza、Paul Knochel
DOI:10.1016/s0022-328x(03)00237-7
日期:2003.8
Applications of the boron–zincexchange reaction to make new carboncarbon bonds are reviewed. Functionalized chiral secondary alkylzinc reagents can be prepared by this exchange reaction and allows to perform formal enantioselective Michael-additions with umpolung of reactivity. The scope of substrate controlled diastereoselectivehydroborations can be considerably enhanced by this methodology. A