Frederick E. Ziegler

A Mild Method for the Esterification of Fatty Acids

Abstract In conjunction with a synthetic problem, we were in need of a method for the stoichiometric esterification of fatty acids, containing the aqueous acid labile tert-butyl dimethylsilyloxy group (OTBS), with a variety of alcohols. It has been reported2 that fatty acids form acylureas in the presence of dicyclo-hexylcarbodiimide (DCC) and methanol3 without esterification.

A C6, C7 oxygen functionalized intermediate for the synthesis of forskolin: stereochemical control in an intramolecular Diels-Alder reaction

Abstract Stereospecific intramolecular Diels-Alder reactions of aldehydes 3a and 3b afford lactones 4 and 5 , respectively. The mechanism of the reactions is considered. Lactone 4 is elaborated further to provide acetonide 14b , an important intermediate in an approach to the synthesis of forskolin ( 1 ).

A palladium-catalyzed carbon-carbon bond formation of conjugated dienones : A macrocyclic dienone lactone model for the carbomycins

Abstract A Pd catalyzed coupling of terminal vinylic iodides with methyl vinyl ketone and related enones to produce dienones is described. The application of this method to macrocyclization is demonstrated in a model system for the agylcone of carbomycin B.

The stereocontrolled photoaddition of allene to cyclopent-1-ene-1-carboxaldehydes. A total synthesis of (±) steviol methyl ester and isosteviol methyl ester

Abstract The stereochemistry of the photoaddition of allene to hydroindenal 19 is explored. The stereochemistry is proven by conversion into steviol methyl ester 22b and isosteviol methyl ester 24 .

Acyclic stereocontrol via the claisen rearrangement: a formal synthesis of (+) tirandamycic acid

Abstract The optically active lactone 1a, prepared previously by the claisen rearrangement, serves as a starting material for the synthesis of (−) alcohol 7b which has been ultilized by Ireland in the synthesis of tirandamycic acid 8a.

A synthesis of (+)-9a-desmethoxymitomycin A via aziridinyl radical cyclization

Abstract A synthesis of (+)-desmethoxymitomycin A is described. The critical step is a highly stereoselective cyclization of an aziridinyl radical to afford a tetracycle having the same relative and absolute stereochemistry as mitomycin A and C.

Regiochemical control in the hemiacetalization of a dihydroxydialdehyde. An application of the use of homochiral 3-methyl-δ-butyrolactones to the construction of homochiral tripropionate units.

Abstract A method for the inversion of lactone homochirality and subsequent chain extension of dipropionate to tripropionate units is discussed. The synthetic sequence leads to (+)-methyl Prelog-Djerassi lactonic acid.

Functionalized cyclopentanes via radical cyclizations using thiocarbonate derivatives as initiators and terminators

Abstract A radical-based cyclization is described that employs xanthates or cyclic thionocarbonates as initiators and allylic dithiocarbonates or allylic thiocarbamates as terminators.

R-3-methyl-γ-butyrolactone as a template for the synthesis of (+)-invictolide

Abstract The dextrorotatory antipode of the pheromone invictolide has been synthesized from R-3-methyl-γ-butyrolactone, which is employed as a stereochemical template for the addition of propionate units via a Claisen rearrangement and a palladium-catalyzed alkylation. (+)-Invictolide is inactive.

On the extent of racemization of allylic esters during palladium—mediated alkylation with homochiral 3-methyl-δ-butyrolactone derivatives

Abstract The allylic phosphate 4e has been shown to racemize 4–6% upon alkylation with the sodium lactone enolates of 1c and ent-1c in the presence of Pd(Ph3P)4. The acetate 4d racemizes 11%.