Process for the preparation of certain triaryl rhamnose carbamates
View Patent ↗Triaryl rhamnose carbamate insecticides are prepared from triaryl acyl azides and tetrahydropyran-2-ols in good yield without the use of a hydride base.
1. A process for preparing triaryl rhamnose carbamates of the Formula (I),
wherein
R 1 represents (C 1 -C 6 )haloalkyl or (C 1 -C 6 )haloalkoxy, and
R 2 represents (C 1 -C 6 )alkyl, (C 2 -C 6 )alkenyl or (C 2 -C 6 )alkynyl,
which comprises
a) rearranging a triaryl acyl azide of Formula (II)
wherein
R 1 is as previously defined,
to an isocyanate of Formula (III)
wherein
R 1 is as previously defined,
by heating at a temperature of about 60° C. to about 110° C. in an anhydrous aprotic solvent, and
b) contacting the isocyanate of Formula (III) with a tetrahydropyran-2-ol of Formula (IV)
wherein
R 2 is as previously defined,
in a polar aprotic solvent in the presence of cesium carbonate.
2. The process of claim 1 in which R 1 is a (C 1 -C 2 )fluoroalkoxy group.
3. The process of claim 1 in which R 2 is CH 2 CH 3 , CH 2 CH 2 CH 3 or CH 2 CH═CH 2 .
4. The process of claim 1 in which the isocyanate of Formula (III) is prepared and used in situ.
5. The process of claim 1 or 4 in which the anhydrous aprotic solvent and the polar aprotic solvent are a mixture of an aromatic hydrocarbon and a nitrile.
6. The process of claim 5 in which the anhydrous aprotic solvent and the polar aprotic solvent are a mixture of toluene and acetonitrile.