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13C NMR studies of dianions of unsaturated carboxylic acids by MaJosé Aurell; Salvador Gil; Ramon Mestres; Margarita Parra; Amparo Tortajada is a Chemistry article available to read on EtoBox.

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13C NMR Spectra of the diions Li2-n resulting from doable deprotonation of unsaturated carboxylic acids I to 6 by lithium dialkylamides, are examined. Higher field resonance for C2 than for C4 atoms are observed, which x-veal higher electron density at C2 than at C4, in agreement with the kinetic a-regioselectivity exhibited by these dianions on reaction with electropbiles. Unsaturated carboxylic acids are synthetically usetul building blocks. On deprotonation by two equivalents of lithium dialkylamides they atford dianions (Lip) that react as ambident nucleophiles through their a or y carbon atoms leading to single or clearly predominant compounds when allowed to react with electrophiles under adequate conditions lm3. Regioselectivity trends depend on the electrophile as well as on reaction conditions (see Scheme 1 for butenoic acids). Thus, a attack predominates in the irreversible reaction with aIky1 halides and hydronium ion 4,s, and in reversible additions to aldehydes and ketones under kinetic conditions, but y-adducts are obtained when these additions are carried out under equilibrium conditions h-\*0. Stereoselectivity for y-attack is usually very high, and most frequently

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Author

MaJosé Aurell; Salvador Gil; Ramon Mestres; Margarita Parra; Amparo Tortajada

Publisher

Elsevier Science; Elsevier ; Elsevier Ltd.; Elsevier BV (ISSN 0040-4020)

Published

1994

Language

EN

Field

Chemistry (Physical Sciences)