F. Bigi et al. / Tetrahedron 56 (2000) 2709±2712
2711
The formylation process was then extended to different
phenols. Interestingly, with monosubstituted phenols
[RCH3, (CH3)3C; R0H] the formylation exclusively
occurred at the ortho position (Table 1).
3-tertButyl-salicylic aldehyde (6d). Pale yellow oil, bp
247±248.58C (lit13a bp 2488C).
3-Methyl-5-decyl-salicylic aldehyde (6e). Pale yellow oil,
bp 37±388C/0.07 mm Hg; H NMR (300 MHz, CDCl3) d
1
The ortho-regioselectivity of the process could be ration-
alised, assuming the formation of an activated complex
resulting from an H-bond between formaldehyde and the
OH group of the phenol co-ordinated to the catalyst
surface.17
0.80 (3H, t, J6.6 Hz, CH3CH2), 1.19 (14H, br s, 7 CH2),
1.5 (2H, m, CH2CH2Ar), 2.17 (3H, s, CH3Ar), 2.47 (2H, t,
J7.7 Hz, CH2Ar), 7.08 (1H, d, J2.0 Hz, H-6), 7.13 (1H,
br s, H-4), 9.76 (1H, s, CHO), 11.01 (1H, s, OH); IR (NaCl)
3103 (OH), 1654 (CvO) cm21; MS m/z (M1) 276 (15%),
149 (100%), 41 (13%). Anal. calcd for C18H28O2: C, 78.2;
H, 10.2. Found: C, 78.1; H, 10.3.
Finally, we faced the problem of the catalyst recycle. After
®ltration and washing with methanol, the montmorillonite
KSF was effective only for one cycle, promoting the model
reaction in 36% yield.
Acknowledgements
In conclusion, the discovery and development of this
catalytic reaction have led to a new method for the direct
formylation of phenols in good yield and high selectivity
under environmentally friendly conditions.
Á
The authors thank the Ministero dell'Universita e della
Ricerca Scienti®ca e Tecnologica (MURST), Italy, the
Consiglio Nazionale delle Ricerche (CNR), Italy and the
University of Parma (National Project Stereoselezione in
Sintesi Organica. Metodologie ed Applicazioni) for ®nan-
cial support. The authors are also grateful to the Centro
Á
Interfacolta Misure (C.I.M.) for the use of NMR and Mass
Experimental
instruments and to Mr Pier Antonio Bonaldi for technical
assistance.
Melting and boiling points were obtained on an Electro-
thermal melting point apparatus and are uncorrected. IR
spectra were recorded on a Nicolet PC5 spectrophotometer.
1H NMR spectra were recorded on a Bruker AC300 at
300 MHz. Chemical shifts are expressed in ppm relative
to TMS as internal standard. Mass spectra were obtained
on a Hewlett±Packard HP-5971 A instrument in EI mode
at 70 eV. Microanalyses were carried out by Dipartimento
di Chimica Generale ed Inorganica, Chimica Analitica,
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Á
Chimica Fisica dell'Universita di Parma. TLC analyses
were performed on Merck 60 PF254 silica gel plates using
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Synthesis of salicylic aldehydes 6. General procedure
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1.4 ml) and montmorillonite KSF (1.5 g) in toluene (5 ml),
was heated at 1008C in a small autoclave under ef®cient
stirring. After 4 h the reaction mixture was cooled to rt,
the catalyst was ®ltered and washed with boiling methanol
(3£50 ml); the solvents were distilled off and the crude was
puri®ed by ¯ash chromatography using as eluant mixtures
of hexane/ethyl acetate (5±10%). All the known products
(6a±d) gave spectral data consistent with the reported ones.
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3-tertButyl-5-methyl-salicylic aldehyde (6a). Pale yellow
oil, bp 110±1128C/7 mm Hg (lit6 bp 128±1308C/
16 mm Hg).
3,5-Ditertbutyl-salicylic aldehyde (6b). Pale yellow solid,
mp 54±568C (lit18 mp 54±568C).
3-Methyl-salicylic aldehyde (6c). Pale yellow oil, bp 210±
2128C (lit13a bp 2118C).
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(b) Chemistry of Waste Minimisation, Clark, J. H., Ed.; Chapman