Electrocyclic processes in aromatic biosynthesis: a biomimetic study of pseudorubrenoic acid A
摘要:
The possible involvement of 6pi electrocyclic ring closures, mediated by electrocyclase enzymes, of polyunsaturated acyclic polyketide intermediates in the biosynthesis of certain o-dialkyl-substituted benzenoid natural products is discussed. The feasibility of the process is illustrated by the electrocyclic ring closure of 7E,9Z,11E,13Z-1-t-butyldimethylsilyloxy-hexadeca-7,9,1 1,13-tetraene (12a) to the cyclohexadiene 13 followed by dehydrogenation to the analogue 14 of the o-dialkyl-substituted aromatic metabolite pseudorubrenoic acid A (1). (C) 2002 Elsevier Science Ltd. All rights reserved.
Titanacyclobutenes or Titanium Vinyl Carbene Complexes? Reactivity of Organotitanium Species Generated by the Reaction of γ-Chloroallyl Sulfides with a Titanocene(II) Reagent
conjugated dienes and vinyl cyclopropanes as major products, thus suggesting the formation of vinyl carbene complexes as intermediates. On the contrary, the organotitanium species generated from acyclic beta,gamma-disubstituted gamma-chloroallyl sulfides revealed titanacyclobutene-like reactivity, and their reaction with 1,5-diphenylpentan-3-one produced homoallyl alcohols. These organotitanium species
The title compounds are prepared by an efficient one-pot reaction involving ring-opening of an epoxide with lithium 3-trimethylsilyl-1-phenylthio-2-propyn-1-ide, tosylation of the intermediate alkoxide, and finally deprotonation. In an alternative approach, intramolecular epoxide ring opening by a ß anion is succesfully applied.
Neutral Sulfur Nucleophiles: Synthesis of Thioethers and Thioesters by Substitution Reactions of N-Heterocyclic Carbene Boryl Sulfides and Thioamides
作者:Xiangcheng Pan、Dennis P. Curran
DOI:10.1021/ol5010164
日期:2014.5.16
Newly discovered boryl sulfides and N-borylthioamides are shown to serve as neutral sources of sulfur nucleophiles in substitutionsreactions. For example, heating of diMe-Imd-BH(SPh)2 with benzyl bromides, primary bromides, or acid chlorides provides the corresponding thioethers or thioesters in high yields. Likewise, N-phenyltetrazole thioethers/esters are made from a readily available N-borylthionotetrazole
Sequential One-pot Reactions of Thioformates with Lithium Silylacetylides, Arylmagnesium Halides, and Electrophiles Leading to Formation of Propargyl Sulfides
One-pot reactions of thioformates with lithium silylacetylides, arylmagnesiumhalides, and electrophiles that produce propargyl (2-propynyl) sulfides are described. The pathway for this process beg...
A new and highly efficient catalytic system based on CpRuClL2 is proposed for the S-propargylation of thiols by propargylic carbonates under neutral conditions, in which specific requirements inherent to the different reactivities of aliphatic and aromatic thiols are achieved by tuning both the nature of the ancillary ligand L and the experimental conditions.