Process for the manufacture of benzene derivatives

Details Process for the manufacture of benzene derivatives Process for the manufacture of benzene derivatives

1986-07-24

1989-02-14

Killos, Paul J.

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acid esters

560 52, 560 60, C07C 6976

Patent

active

048047767

DESCRIPTION:

BRIEF SUMMARY
The present invention is concerned with a novel process for the manufacture of p-tert.butyl-benzene derivatives.
The products obtained according to the process in accordance with the invention are novel intermediates, which are suitable for the manufacture of a known odorant substance, or this odorant substance itself.
The process comprises reacting p-tert.butyl-benzyl chloride with a 2-formylpropionate of the formula ##STR3## wherein R represents lower-alkyl, e.g. C.sub.1-6 -alkyl, especially methyl or ethyl, ##STR4## wherein R has the above significance, optionally after purification, into p-tert.butyl-.alpha.-methyl-hydrocinnamaldehyde by decarbalkoxylation.
p-tert.Butyl-benzyl chloride is accessible in accordance with DT-OS (German Offenlegungsschrift) No. 3,320,020 in an economical in practically pure form. This halide can be oxidized according to Sommelet to give p-tert.butyl-benzaldehyde and the last-mentioned aldehyde can be condensed with propionaldehyde to give p-tert.butyl-.alpha.-methyl-cinnamaldehyde. By hydrogenation of the double bond in the side chain there is obtained the known odorant substance p-tert.butyl-.alpha.-methyl-hydrocinnamaldehyde (U.S. Pat. No. 2,875,131).
The present reaction sequence is more efficient as it avoids above all the Sommelet reaction, which owing to the accumulation of N-compounds such as methylamine and ammonia leads to an undesired pollution of the environment with harmful substances; in addition the energetically-unfavourable sequence oxidation/(condensation)/reduction is avoided.
A further advantage lies in the fact that the reaction products of the individual steps are obtained in sufficient purity that they need not be purified prior to, where applicable, further reactions in accordance with the invention.
It would, indeed, have been simpler and more obvious from p-tert.butyl-benzyl chloride by alkylating propionaldehyde, or masked or modified form of p-tert.butyl-.alpha.-methyl-hydrocinnamaldehyde by alkylating a masked or modified propionaldehyde (e.g. an enamine, an imine etc), but unfortunately these two routes could not be realized.
Finally, it would also have been simpler to convert the compound I via the free acid directly into p-tert.butyl-.alpha.-methyl-hydrocinnamaldehyde, but this route could also not be realized.
The reaction of p-tert.butyl-benzyl chloride with the compound of formula II can be carried out under generally known alkylation conditions.
Thus, the reaction is conveniently carried out in a homogeneous phase, namely in an only slightly polar solvent, e.g. an aliphatic or aromatic hydrocarbon such as pentane, hexane, heptane, octane etc. or benzene, toluene etc. and in the presence of a non-nucleophilic base. Suitable bases are, in particular, metal hydrides such as alkali metal hydrides, e.g. lithium, sodium or potassium hydride, or tertiary alcoholates such as sodium tert.amylate or potassium tert.butylate etc. The presence of a quaternary ammonium compound as a catalyst is advisable, see e.g. Walter E. Keller, Compendium of Phase-Transfer Reactions and Related Synthetic Methods, 1st edition, Fluka AG, CH-9470 Buchs, Switzerland, 1979, 33.
The reaction temperature is not critical, the reaction can be carried out e.g. at room temperature or at an elevated temperature.
The formyl esters of formula I which are formed are novel compounds which are also an object of the present invention.
The optional further reaction of the formyl ester I is carried out in accordance with the invention by decarbalkoxylation, i.e. removal of the carboxylic acid ester group, while avoiding decarbonylation or deformylation.
This decarbalkoxylation of the compound I can be carried out e.g. by firstly converting the compound I into a compound of the formula ##STR5## wherein R has the above significance and R.sup.1 represents a protected formyl group, e.g. an acetal (a dialkoxymethyl group), e.g. dimethyl acetal, diethyl acetal, or a cyclic derivative such as ethylene acetal (2,5-dioxa-cyclopentyl) etc.
The compound I is conveniently acetalized.
This acetaliz

REFERENCES:
Lalande, R. et al., C. R. Acad. Sc. Paris, t, 258, (May 4, 1964), group 8, pp. 4567-4569.
"Compendium of Phase-Transfer Reactions and Related Synthetic Methods", Walter E. Keller, editor, 1st Edition, Fluka AG, Buchs, Switzerland (1979), p. 33.
"Organikum Organisch-Chemisches Grundpraktikum", Collective Authors, 6th Edition, VEB Deutscher Verlag Der Wissenschaften, Berlin, (1967), pp. 366-369, 376-381, 398-405.
F. Elsinger et al., Helv. Chim. Acta 43 (1960), 113-118.
P. Mueller et al., Tett. Letters 1973, 3565-3568.

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