1,3,4-Thiadiazines

Heterocyclic compounds of the formula: ##STR1## wherein either X is --CR.sup.1 R.sup.2 -- and Y is --O--, --S-- or--NHR.sup.3 --, wherein R.sup.1, R.sup.2 and R.sup.3, which may be the same or different, each is hydrogen or alkyl of up to 4 carbon atoms; or X is --O--, --S-- or --NH-- and Y is --CR.sup.1 R.sup.2 -- wherein R.sup.1 and R.sup.2 have the meanings stated above; wherein R.sup.4 and R.sup.5, which may be the same or different, each is hydrogen (but provided that R.sup.4 and R.sup.5 are not both hydrogen), or each is a group defined in claim 1 which is readily convertible into a carboxy group; processes for their manufacture; and pharmaceutical compositions containing them. The compounds possess cardiotonic and/or antihypertensive activity.

What we claim is:

1. A heterocyclic compound of the formula ##STR20## wherein X is --S-- and Y is --CR.sup.1 R.sup.2 -- wherein R.sup.1 and R.sup.2, which may be the same or different, each is hydrogen or alkyl of up to 4 carbon atoms; wherein R.sup.4 and R.sup.5, which may be the same or different, each is hydrogen (but provided that R.sup.4 and R.sup.5 are not both hydrogen), or each has the formula: ##STR21##

--CONHNH.sub.2

--CONR.sup.6 OR.sup.7

--CONR.sup.7 R.sup.8

--COOR.sup.9

wherein R.sup.6 and R.sup.7, which may be the same or different, each is hydrogen, alkyl of up to 4 carbon atoms or arylalkyl of up to 10 carbon atoms; and wherein R.sup.8 and R.sup.9, which may be the same or different, each has the formula:

--CH.sub.2 --OCO--R.sup.11

--CH.sub.2 --OCO--OR.sup.11 ##STR22##

--(CH.sub.2).sub.m OH

--CH.sub.2 O--A--OR.sup.11

--A--NR.sup.12 R.sup.13

--A--COOR.sup.12

--A--CONR.sup.12 R.sup.13

wherein m is an integer from 2 to 4, A is alkylene of from 1 to 4 carbon atoms, R.sup.11 is alkyl of up to 4 carbon atoms and R.sup.12 and R.sup.13, which may be the same or different, each is hydrogen or alkyl of up to 4 carbon atoms; or a salt thereof where appropriate.

2. A heterocyclic compound of the formula: ##STR23## wherein X is --S-- and Y is --CH.sub.2 --; and R.sup.4 has the formula: ##STR24##

--CONHR.sup.8

--COOR.sup.9

wherein R.sup.8 and R.sup.9, which may be the same or different, ech has the formula

--CH.sub.2 OCOR.sup.11 ##STR25##

--(CH.sub.2).sub.m --OH

--(CH.sub.2).sub.m --NR.sup.12 R.sup.13

--CH.sub.2 --O--A--OR.sup.11

--A--COOR.sup.12

--ACON.sup.12 R.sup.13

wherein m is an integer from 2 to 4, A is alkylene of from 1 to 3 carbon atoms, R.sup.11 is alkyl of up to 4 carbon atoms and R.sup.12 and R.sup.13, which may be the same or different, each is hydrogen or alkyl of up to 4 carbon atoms.

3. A heterocyclic compound as claimed in claim 2 wherein m is 2, A is --CH.sub.2, --CH(CH.sub.3)--, --CH.sub.2 CH.sub.2 -- or --(CH.sub.2).sub.3 --, R.sup.11 is methyl, ethyl or t-butyl, R.sup.12, when part of --OR.sup.12, is hydrogen, methyl or ethyl and R.sup.12 and R.sup.13, when part of --NR.sup.12 R.sup.13, are both hydrogen, both methyl or both ethyl.

4. The compound 3-ethoxycarbonylpropyl, 1-ethoxycarbonylethyl, 1-N,N-diethylcarbamoylethyl or pivalyloxymethyl p-(5,6-dihydro-5-oxo-4-H-1,3,4-thidiazin-2-yl)benzoate.

5. A pharmaceutical composition having cardiotonic or antihypertensive activity comprising as active ingredient at least one heterocyclic compound, claimed in claim 1, in association with a pharmaceutically-acceptable diluent or carrier therefor.

6. A composition as claimed in claim 5 which contains, in addition to the heterocyclic compound, one or more drugs selected from sedatives, vasodilators, diuretics, cardiac membrane stabilising agents, agents used in the treatment of Parkinson's disease and other tremors, and cardiotonic agents.

7. A method for the treatment of acute or chronic heart failure in a warm-blooded animal in need of such treatment which comprises administering to said animal an effective amount of a heterocyclic compound claimed in claim 1.

8. The compound pivalyloxymethyl p-(5,6-dihydro-5-oxo-4H-1,3,4-thiadiazin-2-yl)benzoate.