Bradley S. DeHoff

Cembranolide total synthesis. Anisomelic acid

Abstract The stereoselective total synthesis of (±)-anisomelic acid ( 34 ) has been achieved starting from aldehyde 7 , the ozonolysis product of geranyl acetate. Two key steps ensured the stereoselectivity of the synthesis. The first entailed a highly anti-selective addition of the allyltitanium derived from carbamate 15 to aldehyde 5 affording the enol carbamate allylic alcohol 16 . The second was a highly ( Z )-selective Horner-Emmons cyclization of the derived phosphono ester aldehyde 25 leading to the conjugated ester 27 . Further conversion led to the crystalline lactone 30 whose structure was confirmed through single crystal X-ray analysis. Equilibration of the conjugated double bond of 30 gave rise to a 1:1 mixture of the ( Z ) and ( E ) isomers. This result was foretold by molecular mechanics calculations.

Total synthesis of the germacranolide (±)-aristolactone via [2,3] Wittig ring contraction

The total synthesis of (±)-aristolactone (15) is described wherein the key cyclodecenynol precursor 10 is prepared in over 90% yield via a highly regio and stereoselective [2,3] Wittig rearrangement of the 13-membered propargylic ether 9.

Stereoselective synthesis of cembranolide precursors via macrocyclization of α-alkoxyallylstannane aldehydes

Abstract An efficient route to the MOM-protected α-hydroxylallylstannane propargylic aldehyde 15 starting from geraniol is described. Cyclization of 15 to the 14-membered cembranolide intermediate 16 , a 7:1 mixture of cis and trans isomers, is effected in 80% yield with BF 3 ·OEt 2 at −78°C.

Stereoselective total synthesis of the cembranolide diterpene anisomelic acid

Abstract A highly stereoselective total synthesis of the cembranolide diterpene anisomelic acid has been achieved via a convergent route. Macrocyclization was effected by a (Z)-selective intramolecular Horner-Emmons condensation.

A Convenient Two-Step Procedure for Lactone α-Methylenation

Abstract A new procedure for lactone α-methylenation is described in which α-hydroxymethyl lactones are dehydrated with cyclohexyl-3-(2-morpholinoethyl)carbodiimide metho-p-toluenesulfonate-CuCl2 in acetonitrile.