Reagent selection cyclic derivatives formation

Most Shapiro reactions of acyclic sulfonylhydrazones or cyclic sulfonylhydra-zones derived from larger rings proceed with selectivity for the formation of the E-vinyllithium reagent. For example, the trisylhydrazone generated from 4-heptanone (12)... 

Optically active five- or six-membered cyclic A -acyliminium ions of this type are generated from the a-inethoxy derivatives, easily obtainable through anodic methoxylation of intermediates that are prepared via ex-chiral-pool syntheses from certain natural amino acids. Reaction of 5-substituted five-membered cyclic A -acyliminium ions with various nucleophiles leads to the predominant formation of cw-products with moderate selectivity. The trans-selective reaction with alkyl copper reagents appears to be an exception. 

Wilson (1992) described the use of various boronic acids for the derivatiza-tion and separation of ecdysteroids by normal- and reversed-phase TLC. The derivatives were prepared from butyl-, phenyl-, and aminophenylboronic acids by over-spotting a methanolic solution of the reagent on to the applied ecdysteroids at the origin of the TLC plate. Butylboronic acid was also used as a mobile-phase additive to modify chromatographic behavior. A 20,22-diol group was an essential structural requirement for the formation of a cyclic boronate of an ecdysteroid. These procedures allowed for the selective separations of such compounds as ponasterone A and 2-deoxyecdysone. Pis and Harmatha (1992) also described the use of phenylboronic acid as a versatile derivatization agent for TLC studies of ecysteroids. 

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