Química Orgânica 1 · Adição a alcenos e regioquímica
Hydroboration–oxidation of 1-methylcyclohexene
Condições: BH3·THF, THF, 0 °C; then H2O2, NaOH, H2O
Desenhe este problema você mesmo
Arraste dos elétrons que se movem até onde eles vão, ou toque em um e depois no outro. Cada seta é verificada; Dica ajuda quando você travar. Não precisa de conta.
O mecanismo, passo a passo
Próximo mostra as setas curvas de cada passo e as explica. Os passos escritos estão abaixo.
Ler todos os 8 passos escritos
Concerted syn hydroboration
The π pair bonds to boron at the ring CH carbon while a hydrogen moves from boron to the methyl-bearing carbon, all on the same face of the ring.
As setas curvas
- The π pair forms the C–B bond at the ring CH carbon.
- The B–H pair delivers hydrogen to the methyl-bearing carbon.
Cis or trans?
H and B add to the same face, and oxidation keeps the configuration, so the new H and OH are cis to each other, which puts the methyl and OH trans.
Hydroperoxide adds to boron
The hydroperoxide anion, formed from H2O2 and NaOH, fills the empty p orbital on boron.
As setas curvas
- The hydroperoxide oxygen lone pair forms the B–O bond.
Ring carbon shifts from boron to oxygen
The ring carbon migrates from boron to oxygen with its bonding pair as the O–O bond breaks and hydroxide leaves; the carbon keeps its configuration.
As setas curvas
- The C–B pair moves with the ring carbon to oxygen.
- The O–O bond breaks and hydroxide leaves.
Hydroxide adds to boron
Hydroxide adds to the boron of the alkoxyborane, setting up release of the alkoxide.
As setas curvas
- The hydroxide lone pair forms a B–O bond.
The alkoxide is released
The B–O bond to the ring oxygen breaks, giving the cyclohexoxide anion and a hydroxyborane.
As setas curvas
- The B–O bonding pair stays on the alkoxide oxygen.
Water protonates the alkoxide
Water transfers a proton to the alkoxide, giving the alcohol and hydroxide.
As setas curvas
- The alkoxide lone pair bonds to a water hydrogen.
- The O–H pair stays on oxygen as hydroxide.
trans-2-Methylcyclohexan-1-ol
OH is on the former ring CH carbon, next to the methyl-bearing carbon, and trans to the methyl group.
O que você vai praticar
Draw hydroboration of 1-methylcyclohexene with boron on the ring CH carbon, then the oxidation sequence that replaces boron with OH to give 2-methylcyclohexan-1-ol.
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