4,6,6-Trimethyl-1,3-cyclohexadiene-1-carboxaldehyde → 2-Isopropyl-5-methylhexan-1-ol

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Reaction Steps

After comparison of the proton NMR spectral data to published spectral data for dehydrocitral (2) (Kann et al., J. Org. Chem. 55, 5312-5323 (1990)) and 4,6,6-trimethyl-1,3-cyclohexadiene-1-carboxaldehyde (3) (Hong et al., Org. Letters, 8, 2217 (2006)), the mixture was shown to contain dehydrolavandulal (1), (2E,4E)-3,7-dimethyl-2,4,6-octatrienal (2) (dehydrocitral), and 4,6,6-trimethyl-1,3-cyclohexadiene-1-carboxaldehyde (3) in a 76:12:12 ratio, respectively. The proton NMR spectrum of dehydrolavandulal (1) exhibited a singlet at δ 9.44 (CH═O); a doublet (J=12 Hz) at δ 7.10 (vinyl H at C3); a broad doublet (J=12 Hz) at δ 6.35 (vinyl H at C4); broad singlets at δ 5.27 and δ 4.80 (C═CH2); and broad singlets at δ 1.97, 1.94, and 1.90 (three CH3 groups). The proton NMR spectrum of dehydrocitral (2) was characterized by a doublet (J=8.1 Hz) at δ 10.10 (CH═O, E stereoisomer); a doublet of doublets (J=15, 11 Hz) at δ 6.97 (vinyl H at C5); a doublet (J=15 Hz) at δ 6.24 (vinyl H at C4); a broad doublet (J=11 Hz) at δ 6.00 (vinyl H at C6); a broad doublet (J=8.1 Hz) at δ 5.95 (vinyl H at C2); a doublet (J=1.2 Hz) at δ 2.30 (CH3 at C3); and overlapping broad singlets at δ 1.88 (two CH3 groups at C7). The assignment of dehydrolavandulal was further confirmed by hydrogenation of dehydrolavandulal to obtain the known compound tetrahydrolavandulol, as shown in Example 5. The presence of 4,6,6-trimethyl-1,3-cyclohexadiene-1-carboxaldehyde as a minor component in the product mixture was indicated by a singlet at δ 9.40 (CH═O) and a singlet at δ 1.20 (6H; two CH3 groups at C6). For a full spectral characterization of the latter cyclic aldehyde, see B. C. Hong, et al., Org. Letters, 8, 2217 (2006).

Provenance & Evidence