Lignin-type, α,β-unsaturated aldehydes of lignin-type in organic solvents
摘要:
A 1:1 reaction of [HO(CH2)(3)](3)P with 4-hydroxy-3-methoxy-cinnamaldehyde (coniferaldehyde) or 3,5-dimethoxy-4-hydroxycinnamaldehyde (sinapaldehyde) in acetone at room temperature affords phosphonium zwitterions of the type R3P+CH(4-O--Ar)CH2CHO; other phosphines [R = Et, n-Bu, (CH2)(2)CN, and p-Tol] do not react under the same conditions. In alcohols R'OH(D) [R' = CD3, Et, (CD3)(2)CD, s-Bu, HOCH2CH2], the above phosphines (except the cyano-derivative) and those where R = i-Pr, Cy, Me2Ph, MePh2 do react within an equilibrium established between the reactants and the zwitterion-hemiacetal products R3P+CH(4-O--Ar)CH2CH(OH)(OR') that are formed as a mixture of two diastereomers. The nature of the phosphine and the alcohol affects the equilibrium and the diastereomeric ratio.