Solution- and solid-state NMR study of intermediate η3-allyl-cobalt tricarbonyl type complexes in 3-methyl-1,2-butadiene polymerization

Szalontai, Gábor; Sóvágó, Judit; Ungváry, Ferenc

doi:10.1016/s0022-328x(99)00223-5

Cited by 5 publications

(1 citation statement)

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“…Reductive defunctionalizations during Pauson−Khand reactions have been described previously for α-halo cyclopentenone derivatives . It has been suggested that an allylic hydridocobalt complex, derived from the alkyne cobalt complex, is responsible for the reduction of the α-halo ketone 18b. The formation of sulfinamide 8 with inversion of configuration would lend support to the notion that the reduction of 2a − d may be caused at least in part by an allylic hydridocobalt complex derived from 7a − d , since the alternative reduction of 2a − d by a single electron-transfer mechanism should proceed under retention of configuration at the S-atom (Figure ). , Thus, reaction of 2a − d with such a hydridocobalt species could give enolates 10a − d and the S−H sulfoximine 11a .…”

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confidence: 65%

Asymmetric Synthesis of Fused Bicyclic α-Amino Acids Having a Hexahydro-cyclopenta[c]pyridine Skeleton via Intramolecular Pauson−Khand Reaction of 1-Sulfonimidoyl-Substituted 5-Azaoct-1-en-7-ynes

Günter

Gais

2003

J. Org. Chem.

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An asymmetric synthesis of fused bicyclic amino acids having a hexahydro-cyclopenta[c]pyridine skeleton and carrying besides an enone structural element a substituent at the beta-position is described. The key steps of the synthesis are a highly selective allylation of N-tert-butylsulfonyl imino ester with bis(allylsulfoximine)titanium complexes and a highly diastereoselective Pauson-Khand cycloaddition of sulfonimidoyl-substituted gamma,delta-unsaturated alpha-amino acid esters carrying a substituent at the beta-position and a propargyl group at the N-atom. The cyclization is accompanied by a reductive cleavage of the sulfoximine group of the primary cyclization product. Surprisingly, the removal of the sulfoximine group proceeds with inversion of the configuration at the S-atom and gives N-methyl-phenylsulfinamide with >/=98% ee. Deprotection of the bicyclic N-tert-butylsulfonyl-protected amino acid ester was accomplished through treatment with CF(3)SO(3)H under anhydrous conditions. The enantio- and diastereomerically pure sulfoximine-substituted gamma,delta-unsaturated alpha-amino acid esters used as starting material were obtained through a highly regio- and diastereoselective allylation of N-tert-butylsulfonyl imino ester with acyclic bis(allylsulfoximine)titanium complexes, described previously.

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