Method of producing acetals

Details Method of producing acetals Method of producing acetals

1999-11-18

2001-02-06

McKane, Joseph (Department: 1626)

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

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C548S142000, C548S144000, C548S251000

Reexamination Certificate

active

06184383

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method of producing a compound having an acetal skeleton, with good efficiency and a high yield. The compound is useful for a photographic coupler, or as an intermediate in a variety of organic synthesis.
BACKGROUND OF THE INVENTION
Hitherto, synthesis of acetals having the structure shown below has not been sufficiently studied. One general method therefor is described in JP-A-5-313322 (“JP-A” means an unexamined published Japanese patent application).
Specifically, as shown in scheme (I) below, it was a method wherein (A) was subjected to methylolation with paraformaldehyde, to synthesize (B), and the resultant (B) was reacted with mercapto azole in the presence of zinc iodide, to obtain (C) as an objective product.
However, the above-described method had such problems that
(i) Two steps are necessary to obtain the object,
(ii) The yield is low in each of the steps,
(iii) It is extremely difficult to isolate (B) using a means other than column purification, because (B) of an intermediate is synthesized with a low yield and poor crystallinity,
(iv) Paraformaldehyde is adhered onto a cooling tube during the synthesis of (B), and
(v) Unless the purity of (B) is increased, the synthesis reaction of (C) does not go well.
Compared to such a conventional method, JP-A-5-331145 describes a method in which a reaction is efficiently carried out using a metal salt, whose typical example is copper bromide, as a catalyst. However, this method still has such problems that
(1) The yield is not satisfactory, and
(2) It causes a heavy load on environment, at the dealing and disposal of metal salt (heavy metal) used as a catalyst.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of producing acetal compounds, with good efficiency and high yield, which method improves the above-mentioned drawbacks of the conventional methods.
Other and further objects, features, and advantages of the invention will appear more fully from the following description.
DETAILED DESCRIPTION OF THE INVENTION
The above-described object of the present invention has been accomplished by
(1) A method of producing acetals, comprising reacting a compound represented by formula (I), at least one compound selected from a group consisting of a compound represented by formula (II), paraformaldehyde, and trioxane; and a compound represented by formula (III), to synthesize an acetal represented by formula (IV), wherein the reaction is carried out in the presence of an oxidizing agent and an acid;
 wherein R
1
represents an alkyl group, an aryl group, or a heterocyclic group; and R
2
represents an alkyl group or an aryl group;
 wherein R
3
and R
4
each independently represent a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a carbamoyl group, a sulfamoyl group, an aryl group, or a heterocyclic group;
 wherein X
1
represents a group of non-metal atoms necessary to form a 5- or 6-membered nitrogen-containing heterocycle; and M represents a hydrogen atom or a cation (e.g. sodium ion);
 wherein R
1
, R
2
, R
3
, and R
4
each have the same meanings as in formulae (I) and (II), and X
2
represents the same group of atoms as X
1
in formula (III).
As preferable embodiments of the present invention, the following methods can be mentioned:
(2) The method of producing acetals as stated in the above (1), wherein R
1
is represented by formula (VI):
 wherein Ar represents a substituted or unsubstituted alkyl group or aryl group;
(3) The method of producing acetals as stated in the above (1), wherein the oxidizing agent is a peroxide; and
(4) The method of producing acetals as stated in the above (1), wherein the oxidizing agent is a hydrogen peroxide, or an addition product thereof.
Compounds represented by formula (I) are explained below. R
1
represents an alkyl group, (e.g. methyl, tert-butyl, 2-ethylhexyl, decyl, octadecyl, benzyl), an aryl group (e.g. phenyl, 1-naphthyl, 2-naphthyl), or a heterocyclic group (e.g. 3-pyridyl, 2-thienyl, 1-methyl-3-indolyl). Further, these groups may have a substituent. Examples of the substituent include a hydroxyl group, a carbamoyl group (e.g. carbamoyl, dimethylcarbamoyl, propylcarbamoyl, octadecylcarbamoyl, morpholinocarbonyl), an alkoxy group (e.g. methoxy, tert-butoxy, tetradecyloxy), an aryloxy group (e.g. phenoxy, 2-naphthoxy), an alkylthio group (e.g. methylthio, isopropylthio, decylthio), an arylthio group (e.g. phenylthio, 1-naphthylthio), an alkoxycarbonyl group (e.g. methoxycarbonyl, 2-ethylhexyloxycarbonyl, 2-hexyldecyloxycarbonyl, isopropyloxycarbonyl), an aryloxycarbonyl (e.g. phenoxycarbonyl), an acyl group (e.g. acetyl, pivaloyl, benzoyl), a sulfonyl group (e.g. methanesulfonyl, p-toluenesulfonyl), a nitro group, a cyano group, a halogen atom (e.g. fluoro, chloro, bromo), a sulfamoyl group, an acylamino group (e.g. acetylamino, butanoylamino, benzoylamino), a sulfonylamino group, and other amino groups (e.g. dimethylamino). Further, these groups may be further substituted.
R
2
represents a substituted or unsubstituted alkyl group (e.g. methyl, isopropyl, ethyl, hexyl, tetradecyl, benzyl) or aryl group (e.g. phenyl, 1-naphthyl, 2-naphthyl).
Examples of the substituent that R
2
may have are the same as those mentioned as substituents for R
1
.
Next, compounds represented by formula (II) are explained below.
R
3
and R
4
each independently represent a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a carbamoyl group, a sulfamoyl group, an aryl group, or a heterocyclic group. Examples of the aryl group include a phenyl group and a naphthyl group. Examples of the heterocyclic group include a 2-furyl group or a 2-thienyl group. Further, specific examples of other groups besides these groups are those mentioned for R
1
. When R
3
or R
4
represents a group other than a hydrogen atom, the group may further have a substituent.
Preferably R
3
and R
4
each represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a phenyl group. More preferably, at least one of R
3
and R
4
represents a hydrogen atom. Particularly preferably, both R
3
and R
4
represent a hydrogen atom.
Next, compounds represented by formula (III) are explained below.
X
1
represents a group of non-metal atoms necessary to form a 5- or 6-membered nitrogen-containing heterocycle, which may be further condensed with another ring. Further, the nitrogen-containing heterocycle or the condensed ring may have a substituent thereon.
A structure of the nitrogen-containing heterocycle moiety having a mercapto group of the compound represented by formula (III) is preferably represented by formulae (III-1) to (III-8), as shown below. Each bond on the heterocycle of formulae (III-1) to (III-8) represent a bonding site with a hydrogen atom or a substituent.
Among these, (III-1), (III-2), (III-4), (III-5), and (III-6) are preferable, and (III-1) and (III-4) are particularly preferable.
Examples of the substituent include not only those mentioned as substituents for R
1
, but also an alkyl group (e.g. ethyl, butyl, tert-butyl, benzyl) and an aryl group (e.g. phenyl). Further, these groups may further have a substituent. Preferably, the substituent is an alkyl group, an aryl group, an alkylthio group, an alkoxycarbonyl group, or an aryloxycarbonyl group.
Further, when R
1
of the compounds each represented by formula (I) or (IV) is a group represented by formula (VI) shown below, Ar in formula (VI) represents a substituted or unsubstituted alkyl or aryl group.
When Ar represents an alkyl group, specific examples thereof include, for example, methyl, propyl, butyl, decyl, 2-hexyldecyl, octadecyl, isobutyl, and 1,1-dimethylpropyl, which may further have a substituent. Further, when Ar represents an aryl group, specific examples thereof include, for example, phenyl, 1-naphthyl, and 2-naphthyl, which may further have a substituent. When a group represented by Ar

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