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Metal-Containing Heterocycles: Preparation, Properties, Reactions, LXIX Independent Mechanisms of the Cyclocotrimerization of Thiophosphinito Manganese Complexes with Alkynes. - An Easy Access to Five-Membered Heterocycles
Lindner, Ekkehard,Kaess, Volker,Mayer, Hermann A.
, p. 783 - 790 (2007/10/02)
In solution the dimeric thiophosphinitomanganese complexes 1 = Me (1), Et (2), nPr (3)> are in equilibrium with the monomeric species (4-6).For R1 = iPr (7) and Cy (8) the complexes are kinetically stabilized.In THF 4-8 react with different activated alkynes R2CR2 to form the S-isomeric five-membered heterocycles (11a,b,e-i).With additional alkynes R3R2, 11a,b,e-i are transformed into the thiaphosphamanganabicycloheptadienes 12a-i.The less activated alkyne HCCCO2Me inserts regiospecifically into theMn-C bond of 11a,b.The course of the reaction of 7, 8 with activated alkynes is strongly dependent on the polarity of the solvent.In THF the P-isomeric five-membered heterocycles (10g to i) are also obtained.In n-hexane, the P-isomeric seven-membered thiaphosphamanganacycloheptadienes (14g-k) are formed in a cycloaddition of 7, 8 to two molecules of R2CCR2.At elevated temperatures 14g-k eliminate CO with formation of the bicyclic compounds 12g-k.The action of MeCCCO2Me on 8 affords the seven-membered ring 15 in a regiospecific cycloaddition. 12a-d,h,i and 15 are starting compounds for easy access to the different substituted thiophenes 17, 18a-d, furans 19h,i, and the phosphole complexes 20a,b,h,i.
