Development of a general, sequential, ring-closing metathesis/intramolecular cross-coupling reaction for the synthesis of polyunsaturated macrolactones.
A general strategy for the construction of macrocyclic lactones containing conjugated Z,Z-1,3-diene subunits is described. The centerpiece of the strategy is a sequential ring-closing metathesis (RCM) that forms an unsaturated siloxane ring, followed by an intramolecular cross-coupling reaction with a pendant alkenyl iodide. A highly modular assembly of the various precursors allowed the preparation of unsaturated macrolactones containing 11-, 12-, 13-, and 14-membered rings. Although the RCM process proceeded uneventfully, the intramolecular cross-coupling required extensive optimization of palladium source, solvent, fluoride source, and particularly fluoride hydration level. Under the optimal conditions (including syringe pump high dilution), the macrolactones were produced in 53-78% yield as single stereoisomers. A benzo-fused 12-membered-ring macrolactone containing an E,Z-1,3-diene unit was also prepared by the same general strategy. The E-2-styryl iodide was prepared by a novel Heck reaction of an aryl nonaflate with vinyltrimethylsilane followed by iododesilylation with ICl.
Denmark
Scott E
SE
Roger Adams Laboratory, Department of Chemistry, University of Illinois, Urbana, Illinois 61801, USA. sdenmark@illinois.edu
Muhuhi
Joseck M
JM
D018942:Macrolides / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D013237:Stereoisomerism
D018942:Macrolides