The organoalkali route to vitamin A and b-carotene

The reductive cleavage of Me vinyl-b-ionyl ether or the deprotonation of 3,2',6',6'-tetramethyl-5-(1-cyclohexenyl)-1,3-pentadiene gives rise to an organometallic C15 species that combines selectively with a variety of electrophiles at the terminal chain position. Its reaction with aldehydes, however, is less clean. In particular, (E)-b-formyl-2-butenyl acetate gives the expected adduct I and, after dehydration, vitamin A acetate only in poor yield. The same is true for the analogous reaction with 2,7-dimethyl-2,4,6-octatriendial, which ultimately affords b-carotene. Vitamin A acetate can also be prepd., this time in moderate yield, by functionalization through consecutive deprotonation, borylation, oxidn. and acetylation of a C20 pentaene hydrocarbon having the required skeleton. Both the C15 and the C20 organometallic key intermediates adopt spontaneously a zigzag-like outstretched conformation which, upon electrophilic trapping, directly and exclusively leads to the all-(E) configuration. [on SciFinder (R)]

Published in:
European Journal of Organic Chemistry, 20, 3903-3909
CAN 136:102535 30-30 Terpenes and Terpenoids Section de Chimie (BCh), Universite,Lausanne,Switz. Journal 1434-193X written in English. 100-52-7 (Benzaldehyde); 497-03-0 (trans-2-Methyl-2-butenal); 623-27-8 (1,4-Benzenedicarboxaldehyde); 1115-08-8 (3-Methyl-1,4-pentadiene); 5056-17-7; 14398-40-4; 26586-02-7; 59057-30-6 Role: RCT (Reactant), RACT (Reactant or reagent) (organoalkali route to vitamin A and b-carotene); 55497-47-7P; 388075-80-7P; 388075-82-9P; 388075-83-0P; 388075-87-4P; 388075-88-5P; 388075-89-6P Role: RCT (Reactant), SPN (Synthetic preparation), PREP (Preparation), RACT (Reactant or reagent) (organoalkali route to vitamin A and b-carotene); 127-47-9P (Vitamin A acetate); 3917-39-3P; 7235-40-7P (b,b-Carotene); 51468-89-4P; 134436-06-9P; 388075-81-8P; 388075-84-1P; 388075-85-2P; 388075-86-3P; 388075-90-9P; 388075-91-0P Role: SPN (Synthetic preparation), PREP (Preparation) (organoalkali route to vitamin A and b-carotene)

 Record created 2006-03-03, last modified 2018-12-03

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