合成路线1

The formylation of the beta-ionone (I) with methyl formate and NaOMe gives the enol (II), which by reaction with methanol and H2SO4 yields the dimethylacetal (III). The reaction of (III) with methylenetriphenylphosphorane (IV) affords the methylene compound (V), which is treated with formic acid to provide the aldehyde (VI). The condensation of (VI) with isopropylidenemalonic acid dimethyl ester (VII) by means of NaOH gives the polyenic malonic acid (VIII) as a mixture of isomers that is separated by crystallization in ethyl ether to yield the desired all-trans-isomer (IX). Finally, this malonic acid is selectively monodecarboxylated by means of refluxing 2,6-dimethylpyridine to afford the target (E,E,E,Z)-isomer.

合成路线2

The reaction of beta-ionon (X) with triethyl orthoformate (A) by means of H2SO4 in dioxane gives beta-ionon enolether (XI), which by reaction with NBS in CCl4 and hydrolysis with acetic acid is converted into 4-acetoxyonon (XII). The Grignard reaction of (XII) with vinylmagnesium bromide (B) in THF and hydrolysis with KOH in methanol gives 5-(3-hydroxy-2,6,6-trimethylcyclohex-1-en-1-yl)-3-methylpenta-1,4-dien-3-ol (XIII), which is oxidized with MnO2 in methylene chloride yielding 5-(3-oxo-2,6,6-trimethylcyclohex-1-en-1-yl)-3-methylpenta-1,4-dien-3-ol (XIV). Finally, this compound by reaction with triphenylphosphonium bromide (C) in DMF is converted into the phosphonium salt (VIII), which is finally condensed in a Wittig reaction with 2,7-dimethyl-2,4,6-octatriene-1,8-dial (IX) by means of sodium methoxide in dichloromethane.

合成路线3

The aldehyde intermediates (V) and (XII) are produced starting from β-ionone (XXVI) by several different methods. The lithium enolate of ketone (XXVI) is acylated with diethyl chlorophosphate to produce an enol phosphate intermediate, which undergoes regioselective β-elimination in the presence of LDA to furnish acetylene (XXVII). Deprotonation of (XXVII) with butyl lithium followed by treatment with phenyl cyanate gives nitrile (XXVIII), which undergoes conjugate addition of dimethyl cuprate in cold THF to afford the cis-trienenitrile (XXIX). Subsequent reduction of nitrile (XXIX) using DIBALH in hexane at –78 °C provides the target aldehyde (V) as the major isomer (4). Alternatively, Reformatsky reaction of β-ionone (XXVI) with the organo zinc reagent derived from ethyl bromoacetate followed by acidic dehydration produces a mixture of cis- and trans-ionylideneacetates (XXX), which, after saponification to the corresponding carboxylic acids, are separated by fractional crystallization from acetonitrile. The desired cis-isomer (XXXI) is then esterified by treatment with iodomethane and potassium carbonate under nonisomerizing conditions to furnish the cis-methyl ester (XXXIIa) (14). Reduction of ester (XXXIIa) with LiAlH4 in cold THF followed by re-oxidation of the resulting alcohol with MnO2 in CH2Cl2 affords aldehyde (V) (3, 14). The analogous tritium-labeled intermediate is similarly obtained utilizing [3H]-LiAlH4 in the reduction step (3). The tricarbonyliron complex of β-ionone (XXXIII) can be conveniently prepared by treatment of (XXVI) with dodecacarbonyltriiron(0) in boiling benzene. Condensation of (XXXIII) with the lithium enolate of ethyl acetate in cold THF gives the hydroxy ester adduct (XXXIV), which is dehydrated by means of SOCl2 in pyridine to produce the (9Z)-conjugated ester (XXXV) as the major isomer. Reduction of ester (XXXV) with DIBALH in Et2O at –45 °C yields the trienol derivative (XXXVI), which is converted to aldehyde (XII) without decomplexation by mild oxidation of the corresponding bromomagnesium alkoxide with azodicarbonyldipiperidine under Mukaiyama’s conditions. Alternatively, decomplexation of (XXXV) with CuCl2 provides the ethyl ester (XXXIIb), which is reduced to aldehyde (V) following known procedures (5). Scheme 3.

合成路线4

合成路线5