Browsing by Author "Mhehe, George Lukando"

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    Synthesis of Thia-Strigol analogues (potential striga controlling agents)
    (University of Dar es Salaam, 1987) Mhehe, George Lukando
    The use of strigol analogues in the control of Striga and related weeds has been restricted due to the breakdown of these compounds in the soil. Efforts have therefore been directed towards modification of the structure of these compounds in order to enhance the stability under soil conditions, with retention of the desired biological activity. This thesis describes the synthesis of novel strigol analogues in which the enol ether unit in the strigol skeleton has been replaced by an enethiol ether moiely. This thesis describes the synthesis of a number of strigol analogues (Potential Striga controlling agents) in which the enol ether oxygen present in strigol and strigol analogues has been replaced by sulphur. The prepartations of three model analogues, viz.3- (benzylthiomethylidene) - dihydro -2- (3H) - rufanone, 3 - (1 - benzylthiothylidene) - dihydro -2- (3H)- furanone and 2-methyl-4- (2-oxotetrahydrofuran -3-methylidenethio) - but -2-in-4- olide are discribed. These are simple compounds but their preparations demonstrate the possibility of carrying out the desired coupling reaction. The achievement of this coupling, giving products with the correct -geometry around the enethiol double bond, paved a way to the enethiolhalobutenolide coupling reactions required in the synthesis of thia-strigol analogues. The synthesis ofthia-strigol analogues having an aromatic A-ring has been accomplished. The synthesis involved coupling of the sodiomethylidenethiolate derived from the parent lactone 3,3a,4 8b-tetrahydroindeno - /1,2-b/-2-furanone, with 5-chloro -or 5-broms-3-methyl-2-(5H)- furanone. The problems encountered during the coupling are also discussed. Two more strigol analogues have been synthesized using similar coupling procedures. Thioformylation of Corey's lactone, viz.3,3a, 6,6a-tetrahydro-butenolide afforded the bis-lactone strigolanalogue 3-methyl -5- (2-oxo-3,3a,6,6a-tetrahydro-2H-cyclopenta -/b/-furan-3- methylidenethio)-2-(5H)- furanone. In the same manner thioformylation of 2,3,3a,6a-tetrahydor-(4H)-cyclopenta/b/-furan-3-methylidenethio)2- (5H)- furanone. In the same manner thioformylation of 2,3,3a,6a-tetrahydro- (4H)- cyclopenta-/b/-furan-2-one, which is a double bond isomer of Corey's lactone afforded, after the usual coupling, the isometric analogue. The preparation of 6-methoxyindan-1- one-2-acetic acid, a precursor for ring substituted strigol analogue, is described.