Abstract:The conjugate addition of organo-cuprate and -copper reagents to the trans-ester (1) produced the anti-isomer (4a) predominantly, while addition of cuprates to the cis-esters (2 and 3) gave the syn-isomer (5) preferentially, and addition of organocopper compounds to (2) and (3) afforded the anti-isomer (4) predominantly; this change indicates the importance of reagent type in controlling 1,2-asymrnetric induction during conjugate addition.
“…Thus, either syn-91 or anti-93 is formed upon conjugate addition with BF 3 -modified reagents, as a function of enoate geometry. The stereochemistry of the reaction is in accordance with the ''modified'' Felkin-Anh model [40].…”
Section: G-alkyl-substituted a B-unsaturated Carbonyl Derivativesmentioning
“…Thus, either syn-91 or anti-93 is formed upon conjugate addition with BF 3 -modified reagents, as a function of enoate geometry. The stereochemistry of the reaction is in accordance with the ''modified'' Felkin-Anh model [40].…”
Section: G-alkyl-substituted a B-unsaturated Carbonyl Derivativesmentioning
“…In a very similar way to the S N 2‘ reactions, the addition of nucleophiles to γ-chiral-α,β-unsaturated carbonyl compounds can be analyzed (Scheme ). Again, ( E )-alkenes ( E )- 147 preferentially give rise to diastereomer 148 following the Felkin paradigm, while with ( Z )-alkenes ( Z )- 147 1,3-allylic strain is the dominating control element leading to the anti -Felkin diastereomer 149 . , 43 Addition of Nucleophiles to 147 …”
“…Whatever the explanation, the most important result is that the degree of diastereoselectivity is low, in contrast to cuprate additions in the literature, including silylcuprates, in which the substituents on the stereogenic centre were differentiated either by having an electronegative substituent 10,11 or simply by steric effects. 12 Conjugate addition to the second substrates, 14 and 15, followed by protonation of the intermediate enolates 18 and 19, can give four diastereoisomeric products 20, 21, 22 and 23 (Scheme 3). All four were detectable, using distinctive signals in 1 H-NMR spectra, but they were not all easily separable.…”
The bis[dimethyl(phenyl)silyl]cuprate reagent introduces a silyl group to the beta-position of three alpha,beta-unsaturated esters: methyl Z-4-dimethyl(phenyl)silylpent-2-enoate 11, and methyl Z- and E-(1'-dimethylphenylsilylbenzyl)but-2-enoates 14 and 15, diastereoselectively in the unexpected sense, syn to the silyl group in the conformation in which the hydrogen atom is 'inside'. The selectivity is low (58:42) in the first case 11, where the nucleophilic attack is adjacent to the stereogenic centre carrying the silyl group, and moderate (72:28) for both Z- and E-alpha,beta-unsaturated esters 14 and 15, where the nucleophilic attack is at the other end of the double bond from the stereogenic centre. It is conceivable that nucleophilic attack actually takes place in a conformation in which the donor substituent, the silicon-carbon bond, is out of conjugation with the double bond.
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