Generation and Reactions of Alkynylsamariums

Three methods have been developed for generating alkynylsamariums: (1) reduction of iodoalkynes with SmI2 in the presence of HMPA, (2) deprotonation at the terminal position of 1-alkynes either by tetrahydrofurylsamarium generated by PhI and SmI2 in THF, or, (3) deprotonation by butyllithium followed by metal–metal exchange with SmI3. Alkynylsamariums arising from iodoalkynes with SmI2 undergo coupling with carbonyl compounds under both Barbier and Grignard conditions in benzene-HMPA or THF-HMPA as a solvent system. Tetrahydrofurylsamarium generated from iodobenzene and SmI2 in THF can deprotonate from terminal alkynes to yield alkynylsamariums whereas other alkylsamariums, such as ethyl-, isopropyl-, cyclohexyl-, and cyclopentylsamarium do not work well. Metal–metal exchange between an alkynyllithium and SmI3 is also effective; the reactive species in this case would be alkynylsamariums rather than alkynyllithiums. To reveal the properties of alkynylsamariums, we examined the stability and reactivity of alkynylsamariums toward various electrophiles.