Approach to the Synthesis of Chlorothricolide: Synthesis of (±)-19,20-Dihydro-24-O-methylchlorotricolide, methyl ester, ethyl carbonate

Author: Varney, Michael David

Year: 1986

Degree: Dissertation (Ph.D.)

Advisor: Ireland, Robert E.

Committee Members: Dervan, Peter B.; Ireland, Robert E.; Grubbs, Robert H.; Goddard, William A., III

Option: Chemistry

DOI: 10.7907/h9ke-rp15

Abstract

An approach to the total synthesis of the 14-membered macrolide antibiotic aglycon chlorothricolide is presented. Key steps from the two halves to (±)-19,20-Dihydro-24-O methylchlorothricolide, methyl ester, ethyl carbonate include initial esterification across the C1 and C25 carbons followed by macrodilactonization across the C17 and C14 carbons. Ester enolate Claisen rearrangement and subsequent decarboxylation afforded the intact lactone. Functionalization of the top half is explored.

The ester enolate Claisen rearrangement of propionate derivatives of resolved 1-(t-butyldimethylsilyl)-trans-2-butene-1-ol is reported. Subsequent protiodesilation of the reduced and protected Claisen products resulted in the formation of 2,3-dimethyl-4-pentenyl ethers. Thus, the secondary α-silyl alcohol has functioned as a chiral primary alcohol equivalent.

The Claisen rearrangement of vinyl ethyl derivatives of 5-tert-butyl-1-(hydroxymethyl)-1-cyclohexene is reported. The standard allyl vinyl ether conditions as well as the triethyl orthoacetate and ester enolate variants of the Claisen rearrangement all resulted in the formation of cis(axial)-4-tert-butylcyclohexyl-substituted systems. Thus, in sterically unbiased cases, this [3.3] sigmatropic process results in the axial attachment of the side chain in a cyclohexyl system.

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