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Note on a preparation of β, γ‐unsaturated carboxylic acid derivatives using the amide acetal Claisen rearrangement 3‐(Trimethylsilyl)allyl alcohols smoothly undergo the amide acetal Claisen rearrangement furnishing allyl silanes. Subsequent protolysis with HF at −20° provides a convenient, stereoselective method for the preparation of β, γ‐unsaturated carboxylic acid derivatives. Three model examples illustrate the procedure.

1x 74)Sumnzury. Two stercosclcctivc syntheses o f n o n x t i c acid I, the buildmg block of the niacrotetrolide antibiotic nonactin are described. The characteristic cis-configuration of the 2,s-substltuents on the tctrahydrofuran ring of I is obtained in the first synthcsis by catalytic hydrogenation of the furan derivative X. This key intermediate possesses thc carbon skeleton and correct distribution of oxygen functions for convcrsion into nonactic acid. It is synthesized by a n electrophilic substitution of 2-acctonylfuran (VI) with the N-cyclohexyl-N-propcnyl nitrosonium ion (V) generated from the corresponding cr-chloronitrone (VII) and silver fluoroborate, followed by hydrolysis and oxidation of the aldchydc group.Thc sccond synthesis starts with a tliol already having the correct configuration of the side chain that contains the hydroxyl group. For this purpose threo-l-octcn-5,7-diol (XV) is synthesized from acetylacetonc in two steps. Oxidative cleavngc of the tcrminal double bond of this thveo-diol yields a n aldehyde which is converted by a Wittig reaction, with the carbanion, obtained froin clicthyl u-methoxycarbonylethyl phosphonatc, into thc o p i chain intermediate, 2-methy1-6,8dihydroxy-2-nonenoic acid methylester (XV t 1 I). Base-catalyzed cyclisation of this M , B-unsaturatcd dihydroxy cstcr yields thc methyl ester of nonactic acid (I) as the main product.

An enantioselective synthesis of the potent angiotensin-converting enzyme inhibitor (I'S,3S)-3-[( 1'-(ethoxycarbonyl)-3'-phenylpropyl)amino]-2,3,4,5-tetrahydro-2-0~0-1~~ I-benzazepine-I-acetic acid hydrochloride (3) is described which uses a crystallization-based resolution of a racemic amino intermediate with concomitant racemization ofthe unwanted enantiomer.