Selectivity Indium-mediated allylation

1 selectivity

1.1 chemoselective chemistry
1.2 regioselective chemistry
1.3 diastereoselective chemistry
1.4 enantioselective chemistry

selectivity

indium mediated allylations selective, offering 4 different types of selectivity: chemoselectivity, regioselectivity, diastereoselectivity, , enantioselectivity.

chemoselective chemistry

organoindium intermediates not react –oh or –co2h groups. reactions carbonyls, however, give high yields. research has shown in reactions of indium intermediate electrophilic compound of both aldehyde , ketone, reaction proceeded aldehyde. electrophilic compound shown below.

regioselective chemistry

the regioselectivity of allylation mediated indium in water dependent on steric effects of substituents on both intermediate , carbonyl. α-attack nucleophile (at position bearing halogen) distinguishable γ-attack (at double bond) inspecting products. scheme below gives example of 2 different products formed same nucleophile under α-regioselectivity (α) , γ-regioselectivity (γ). regioselectivity not appear depend on conjugation or degree of substitution.

diastereoselective chemistry

the addition of allylindium reagents aldehydes substituted @ α or β carbons can diastereoselective in aqueous systems. example, if chelation control present in α-oxy aldehyde, product expected syn diastereomer. sample reaction of chelation versus non-chelation control illustrated below.

numerous investigations have found explanation effect. oxygens of carbonyl , hydroxyl group chelate indium of organoindium intermediate illustrated below on left 2 green bonds. incipient c-c bond, illustrated in red, creates six-member ring in chair conformation. under chelation control, allyl group attacks carbonyl carbon less hindered side opposite of r group. once c-c bond formed, indium released, producing syn diol. similar chelated structure explains why allylation of β-oxy aldehydes results in anti diols.

from application of allylindium , oxygenated aldehydes, pharmaceutical companies can select specific diastereomeric products. grignard reaction not have advantage because reactive attacks indiscriminately both sides.

enantioselective chemistry

indium capable of affording excellent enantioselectivity when performed in presence of chiral additives. example, 3 effective chiral additives shown below.

the addition of allylindium reagents electrophilic hydrazones, illustrated below, has been reported synthesize 1 enantiomer of chiral product 97% selectivity using binol chiral additive. similarly, chiral amino alcohol allows extremely high enantioselectivity in allylation of ketones.