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Gilman cuprates, reactions with enynes

Highly enantioselective 1,5-substitution reactions of enyne acetates are also possible under carefully controlled conditions (Eq. 4.31) [46]. For example, treatment of enantiomerically pure substrate 70 with the cyano-Gilman reagent tBu2CuLi-LiCN at —90 °C provided vinylallene 71 as a 1 3 mixture of E and 2 isomers with 20% and 74% ee, respectively. This mediocre selectivity might be attributable to race-mization of the allene by the cuprate or other reactive copper species formed in the reaction mixture. The use of phosphines as additives, however, can effectively prevent such racemizations (which probably occur by one-electron transfer steps) [47]. Indeed, vinylallene 71 was obtained with an ee of 92% for the E isomer and of 93% for the 2 isomer if the substitution was performed at —80 °C in the presence of 4 eq. of nBusP. Use of this method enabled various substituted vinylallenes (which are interesting substrates for subsequent Diels-Alder reactions Sect. 4.2.2) to be prepared with >90% ee. [Pg.162]

Allenic amino acid derivatives 50, which are of special interest as selective vitamin Bg decarboxylase inhibitors [35], are accessible through 1,6-cuprate addition to 2-amino-substituted enynes 49 (Eq. 4.22) [36]. Because of the low reactivity of these Michael acceptors, however, the reaction succeeds only with the most reactive cuprate the t-butyl cyano-Gilman reagent tBu2CuLi-LiCN. Nevertheless, the addition products are obtained with good chemical yields, and selective deprotection of either the ester or the amino functionality under acidic conditions provides the desired target molecules. [Pg.157]


See other pages where Gilman cuprates, reactions with enynes is mentioned: [Pg.62]    [Pg.672]    [Pg.153]    [Pg.153]    [Pg.153]    [Pg.153]    [Pg.511]    [Pg.512]    [Pg.512]    [Pg.527]    [Pg.153]    [Pg.672]    [Pg.672]    [Pg.67]    [Pg.148]   
See also in sourсe #XX -- [ Pg.671 , Pg.672 ]

See also in sourсe #XX -- [ Pg.671 , Pg.672 ]

See also in sourсe #XX -- [ Pg.671 , Pg.672 ]




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Cuprate, 3- -, reaction with

Enynes

Gilman

Gilman cuprate

Gilman cuprates, reactions

Gilman reaction

With cuprates

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