- Low-energy pathway for Pauson-Khand reactions: Synthesis and reactivity of dicobalt hexacarbonyl complexes of chiral ynamines
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A family of dicobalt hexacarbonyl complexes of 1-(dialkylamino)-2-(trimethysilyl)acetylenes (3a-f) derived both from achiral and chiral amines [a, morpholine; b, (S)-2-methoxymethylpyrrolidine; c, (2R,5R)-2,5-bis(methoxymethyl)pyrrolidine; d, (±)-trans-2,5-bis(benzyloxymethyl)pyrrolidine; e, (2R,5R)-2,5-dimethylpyrrolidine; f, (S)-(α-methylbenzyl)benzylamine] has been prepared by a one-stage process from dichloroacetylene. The methanolysis at room temperature of these complexes (MeOH/K2CO3) induces the selective cleavage of the carbon-silicon bond, leading to the thermally unstable terminal ynamine complexes 12a-f. The Pauson-Khand reaction of 12a-f with strained olefins (norbornadiene and norbornene) takes place at unprecedentedly low temperatures (-35 °C) in the absence of chemical promoters. Diastereoselectivities of up to 94:6 are recorded in these reactions with the ynamine complexes derived from C2 symmetrical chiral auxiliaries (12c,d). The high reactivity depicted by terminal ynamines in the Pauson-Khand reaction has been analyzed by theoretical semiempirical procedures [PM3(tm)] and with density functional theory (VWN/B88), and appears to reflect an easy CO loss from the ynamine-dicobalt hexacarbonyl complexes.
- Balsells,Vazquez,Moyano,Pericas,Riera
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p. 7291 - 7302
(2007/10/03)
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- α-Sulfinylamidines by the Reaction of Ynamines with N-(Sulfinyl)arenesulfonamides
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in spite of very different substitution the ynamines 1a-q react with the N-(sulfinyl)arenesulfonamides 2a-c to give the α-sulfonylamidines 4.In on e case we succeeded to isolate both of the configutrtion isomers (E- and Z-4i).The structure of the sulfines 4 is confirmed by spectroscopic data and by some reactions: hydrolysis, photolysis, oxidation, and reaction with 2,3-dimethyl-1,3-butadiene of some sulfines 4 furnish the analogous methylene compounds 5 (exception 6), the 2-oxoamidines 7, and the Diels-Alder adducts 8.
- Kosack, Steffen,Himbert, Gerhard
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p. 833 - 842
(2007/10/02)
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