126249-06-7Relevant articles and documents
Total syntheses of the gregatins A-D and aspertetronin A: Structure revisions of these compounds and of aspertetronin B, together with plausible structure revisions of gregatin E, cyclogregatin, graminin A, the penicilliols A and B, and the huaspenones A and B
Burghart-Stoll, Heike,Brueckner, Reinhard
supporting information; experimental part, p. 3978 - 4017 (2012/10/18)
Comprehensive comparisons of 1H and 13C NMR chemical shift values in the furanone cores a, b, and c provide plausible support for a reassessment of the furanone nuclei of the title compounds from b to c. Total syntheses via enantiomerically pure lactic esters were based on the Seebach-Frater "self-reproduction of stereocenters" methodology. Attachment of the hexadienyl side-chain in a trans,trans-selective manner was achieved by addition of the Seebach-Frater enolate to trans-hex-4-en-1-al rather than to trans-hex-3-en-1-al. The type-c furanone cores of the synthetic materials were reached by single or double acylation of a model γ-hydroxy-β-oxo ester (compound 50) and its hexadiene-containing counterpart 29. Our syntheses confirmed the novel connectivities in six compounds. In addition, they required revision of the configuration of a quaternary carbon atom in five cases. Moreover, they allowed elucidation of the configurations of four previously unassigned stereocenters. Hindsight analyses of why the furanone cores of the title compounds had been misinterpreted as a and/or b instead of c are given. Why the stereocenters in the heterocycles had been incorrectly configured, on the bases (a) of relay studies in the 1960s, and (b) of a 1984 total synthesis of gregatin B, is also discussed.
Total synthesis of the calphostins: Application of Fischer carbene complexes and thermodynamic control of atropisomers
Merlic,Aldrich,Albaneze-Walker,Saghatelian,Mammen
, p. 1297 - 1309 (2007/10/03)
The total syntheses of the potent protein kinase C inhibitors calphostins A, B, C, and D as well as a variety of structural analogues are reported. An aminobenzannulation reaction of an enantiopure chromium Fischer carbene complex is utilized to prepare a pentasubstituted naphthylamine. After optimization of side-chain substituents, conversion of the naphthylamine to an o-naphthoquinone was followed by biomimetic oxidative dimerization using trifluoroacetic acid and air yielding a 1:2 P/M mixture of atropisomeric perylenequinones. Thermal equilibration to a 3:1 P:M atropisomeric ratio and separation of the perylenequinones followed by side chain desymmetrization and functionalization led to the total synthesis of enantio- and diastereomerically pure calphostin C in only twelve steps from commercially available starting materials. In addition, calphostins A, B, D, and several structural analogues were prepared to evaluate biological activities.
Mechanism of an Acid Chloride-Imine Reaction by Low-Temperature FT-IR: β-Lactam Formation Occurs Exclusively through a Ketene Intermediate
Lynch, Joseph E.,Riseman, Stephen M.,Laswell, William L.,Tschaen, David M.,Volante, Ralph P.,et al.
, p. 3792 - 3796 (2007/10/02)
The reaction of acid chloride 8 with imine 9 in the presence of a base to form 2-azetidinones 10 and 11 was examined by low-temperature FT-IR spectroscopy.The rate constants for formation of the ketene 12 from the acid chloride and base and for subsequent reaction of this ketene with the imine were measured.From the kinetic data we conclude that the azetidinone products arise completely from the ketene intermediate and not via direct acylation of the imine with the acid chloride.
