Process for preparing an enol silyl ether compound

Details Process for preparing an enol silyl ether compound Process for preparing an enol silyl ether compound

1990-09-10

1991-12-10

Shaver, Paul F.

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

Organic compounds

Diazo or diazonium

C07C11300

Patent

active

050719661

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
The present invention relates to a process for preparing an enol silyl ether compound which is a useful intermediate for use in synthesis of carbapenem .beta.-lactam antibiotics, typically thienamycin, known as .beta.-lactam antibiotics of the fourth generation.
2. Background Art
Generally a diazo compound having the general formula (V): ##STR4## wherein R.sup.7 is a protecting group for carboxyl group and R.sup.5 is hydrogen atom or a protecting group for hydroxyl group, is well known as an intermediate for synthesis of the carbapenem .beta.-lactam antibiotics. It is also known that the compound of the formula (V) is readily synthesized in a good yield by the synthetic method shown in the following reaction scheme: ##STR5## wherein R.sup.5 and R.sup.7 are the same as defined above, R.sup.6 is a trialkylsilyl group, and L is a releasing group (cf., for example, Tetrahedron Letters, 23, 2293 (1982), Journal of the American Chemical Society, 103 (22), 6765 (1981), Japanese Unexamined Patent Publication No. 59-170096).
The present inventors earlier developed a simple method for preparing 4-acetoxy-3-hydroxyethylazetidin-2-one derivative used in the above-mentioned reaction (cf. Japanese Unexamined Patent Publication No. 61-18791 and No. 61-18758).
Accordingly, an enol silyl ether compound from a diazoacetoacetic acid ester, which is the desired compound of the present invention, is useful as an intermediate for synthesis of carbapenem .beta.-lactam antibiotics.
Heretofore an enol silyl ether from a diazoacetoacetic acid ester was synthesized by using a triorganosilyl halide as a silylating agent in the presence of a strong base, e.g. lithium hexamethyldisilazide, according to the following reaction: ##STR6## wherein R.sup.7 is the same as defined above, and R.sup.8, R.sup.9 and R.sup.10 are the same or mutually different and each is an alkyl group having 1 to 4 carbon atoms (cf. Japanese Unexamined Patent Publication No. 58-103358).
The above reaction has a drawback that in the case that R.sup.7 is p-nitrobenzyl group, a strong base cannot be used.
It is reported that in the case that R.sup.7 is p-nitrobenzyl group, a corresponding enol silyl ether can be synthesized when the reaction is carried out using a silylating agent such as triorganosilyl triflate in the presence of trialkylamine (cf. Japanese Unexamined Patent Publication No. 59-170096).
However, such a silylating agent as triorganosilyl triflate causes the following problem in addition to problems in handling when it is used in large quantities. An aqueous solution containing fluorine-containing compounds such as trifluoromethanesulfonic acid which is generated in washing after the reaction cannot be drained as a waste water as it is. Although the solution must be subjected to a suitable treatment, it is not easy to conduct such a treatment.
In view of the above situation, the present inventors made extensive researches to solve the problems mentioned above and it has been found that when a diazoacetoacetic acid ester is reacted with a trialkylsilyl chloride in the presence of an organic base and an alkali halide, the diazoacetoacetic ester can be readily converted in a high yield into an enol silyl ether thereof, which leads to the completion of the present invention.


DISCLOSURE OF THE INVENTION

The present invention provides a process for preparing an enol silyl ether compound from a diazoacetoacetic acid ester having the general formula (IV): ##STR7## wherein R.sup.1 is a lower alkyl group having 1 to 6 carbon atoms, phenyl group, a substituted phenyl group, an aralkyl group or allyl group, and R.sup.2, R.sup.3 and R.sup.4 are the same or mutually different and each is a lower alkyl group having 1 to 6 carbon atoms, which comprises reacting a diazoacetoacetic acid ester having the general formula (I): ##STR8## wherein R.sup.1 is the same as defined above, with a trialkylsilyl chloride having the general formula (II): ##STR9## wherein R.sup.2, R.sup.3 and R.sup.4 are the same as defined above, in an inert solvent

REFERENCES:
patent: 4525582 (1985-06-01), Amato et al.
patent: 4683296 (1987-07-01), Ueda et al.

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