The reaction of the C=N bond in PhCH=NPh with the carbanionic species Ph2PCH2-, leading to the N-phenyl beta-aminophosphine Ph2PCH2CH(Ph)NHPh, L1, is described. This molecule reacts with different organic electrophiles to afford related compounds Ph2PCH2CH(Ph)NPhX (X = SiMe3, L2; COPh, L4), [Ph2MePCH2CH(Ph)NHPh]+(I-), L3, and [Ph2PCH2CH(Ph)N(Ph)CO]2, L5, containing two amido and two phosphino functions. The coordination properties of L1, L2, and L4 have been studied in palladium chemistry. The X-ray structure of [PdCl2(Ph2PCH2CH(Ph)NHPh-kappaP,kappaN)] shows the bidentate coordination mode for the L1 ligand with equatorial C(Ph)-N(Ph) phenyl groups. [PdCl2(Ph2PCH2CH(Ph)NHPh-kappaP,kappaN)] crystallizes at 298 K in the space group P2(1)/n with cell parameters a = 10.689(2) A, b = 21.345(3) A, c = 12.282(2) A, beta = 90.294(12) degrees, Z = 4, D(calcd) = 1.526. The reaction between 2 equiv of L1 and [PdCl(eta3-C3H5)]2 affords the [PdCl(eta3-C3H5)(Ph2PCH2CH(Ph)NHPh-kappaP)] complex in which an unexpected N-H.Cl intramolecular interaction has been observed by an X-ray diffraction analysis. [PdCl(eta3-C3H5)(Ph2PCH2CH(Ph)NHPh-kappaP)] crystallizes at 298 K in the monoclinic space group Cc with cell parameters a = 10.912(1) A, b = 17.194(2) A, c = 14.169(2) A, beta = 100.651(9) degrees, Z = 4, D(calcd) = 1.435. Neutral and cationic alkyl or allyl palladium chloride complexes containing L1 are also reported as well as a neutral allyl palladium chloride complex containing L4. Variable-temperature 31P[1H] NMR studies on the allyl complexes show that the eta3/eta1 allyl interconversion is enhanced by a positive charge and also by a N-H.Cl intramolecular interaction.
The acceptor-substituted 1,2-thiaphospholes 1 react regioselectively with the electron-rich acetylenes 2 at −78°C by [2+2] cycloaddition to afford the novel heterobicyclic compounds 4. As demonstrated by the examples of their reactions with nonacarbonyldiiron(0) and the pentacarbonyltungsten fragment, compounds 4 are able to function as ligands in complex compounds. In addition, the electron-rich double bond in the bicyclic compound 4a is amenable to further reactions. Hence, treatment with mesitylenecarbonitrile
A novel approach to the tricyclic core of the Stemona alkaloids stemofoline and didehydrostemofoline has been discovered that features an intramolecular (3+2) dipolar cycloaddition of an unactivated carbon-carbon double bond with an azomethine ylide; the azomethine ylide was generated by an unprecedented reaction that occurred during a Swern oxidation of an α-(N-cyanomethyl)-β-hydroxy ester. In separate experiments, the efficacy of introducing the requisite oxygen functionality at C(8) and the 1-butenyl side chain at C(3) was established. Keywords Azomethine ylide; Dipolar cycloaddition; Alkaloid synthesis; Remote functionalizationThe roots and leaves of the Stemonacea species have been used extensively in traditional oriental medicine as insecticides and to treat respiratory diseases and parasitic infestation.i Stemofoline (1) was the first alkaloid isolated from Stemona japonica , ii and didehydrostemofoline (2), which was originally named asparagamine A because the plant from which it was isolated was erroneously thought to be Asparagus racemosus, was reported afterwards.iii , iv Isostemofoline and isodidehydrostemofoline, the 11,12-E isomers of 1 and 2, respectively, have also been isolated.v Both 1 and 2 exhibit powerful insecticidal activity as insect acetylcholine receptor antagonists.iv , vi Moreover, 2 exhibits nanomolar activity against different human carcinoma cell lines and possesses potent in vivo antioxytocin activity.iiib , vii These structurally intricate and biologically interesting targets have attracted considerable interest from the synthetic community.viii However, the only total syntheses that have been recorded for alkaloids of this family are of (±)-isostemofoline by Kendeix and of racemic 2 and (±)-isodidehydrostemofoline by Overman.xIn developing an approach to 1 and 2, we were intrigued by the possibility of forming the tricyclic core embodied in 4 by a (3+2) dipolar cycloaddition involving an azomethine ylide 5 that might be generated in situ by silver ion promoted decyanation and deprotonation of Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Supplementary DataExperimental procedures and characterization data for all new compounds are provided. Supplementary data associated with this article can be found in the online version at doi:(Insert doi). the chiral amino nitrile 6 (Scheme 1).xi The subsequent transformation of 4 into the advanced intermediate 3 would then require a remote functionalization xii followed by introduction of the requisite lactone ring. A variety of options were then envisioned for converting 3 into the targeted ...
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