Polyenes

14,000,000 Leading Edge Experts on the ideXlab platform

Scan Science and Technology

Contact Leading Edge Experts & Companies

Scan Science and Technology

Contact Leading Edge Experts & Companies

The Experts below are selected from a list of 237 Experts worldwide ranked by ideXlab platform

Mitchell P. Croatt - One of the best experts on this subject based on the ideXlab platform.

  • Palladium-Catalyzed Chemoselective Protodecarboxylation of Polyenoic Acids.
    Organic Letters, 2018
    Co-Authors: Mohammed H. Al-huniti, Mark A. Perez, Matthew K. Garr, Mitchell P. Croatt
    Abstract:

    Conditions for the first palladium-catalyzed chemoselective protodecarboxylation of polyenoic acids to give the desired Polyenes in good yields are presented. The reactions proceed under mild conditions using either a Pd(0) or Pd(II) catalyst and tolerate a variety of aryl and aliphatic substitutions. Unique aspects of the reaction include the requirement of phosphines, water, and a polyene adjacent to the carboxylic acid.

  • Palladium-Catalyzed Chemoselective Protodecarboxylation of Polyenoic Acids
    2018
    Co-Authors: Mohammed H. Al-huniti, Mark A. Perez, Matthew K. Garr, Mitchell P. Croatt
    Abstract:

    Conditions for the first palladium-catalyzed chemoselective protodecarboxylation of polyenoic acids to give the desired Polyenes in good yields are presented. The reactions proceed under mild conditions using either a Pd(0) or Pd­(II) catalyst and tolerate a variety of aryl and aliphatic substitutions. Unique aspects of the reaction include the requirement of phosphines, water, and a polyene adjacent to the carboxylic acid

William S Johnson - One of the best experts on this subject based on the ideXlab platform.

  • the first examples of nonenzymic biomimetic polyene pentacyclizations total synthesis of the pentacyclic triterpenoid sophoradiol
    Journal of Organic Chemistry, 1994
    Co-Authors: Paul V Fish, William S Johnson
    Abstract:

    The first examples of nonenzymic, biomimetic, polyene pentacyclizations are reported. A series of closely related (E,E,Z,Z)-Polyenes 10–13 with the same tetraene carbon backbone but with differing initiator groups were synthesized and cyclized. The Polyenes 10–12 were all synthesized from the known bromo triene 14 using established protocol. Polyene 13 was prepared from aldehyde 16 by reaction of 16 with (1-methyl-1-cyclopropyl)magnesium bromide to give cyclopropylcarbinol 21. Rearrangement of 21 with MgBr 2 to bromide 22 and then alkylation of the lithium enolate of ethyl 3,3-dimethylacrylate with 22 furnished 23. Isomerization of the double bond into conjugation with the ester and dimethylation of enoate 24 gave 13. Polyene acetal 10 was cyclized with SnCl 4 to pentacycles 26 (4β:4α, 5.5:1) in 51% isolated yield accompanied by regiospecific in situ dehydrofluorination. Polyene 11, with the aldehyde initiator, was cyclized with SnCl 4 to yield alcohols 27 (4β:4α, 5.4:1) in 49% yield, again with loss of HF. Cyclization of the epoxide 12 using the preferred conditions of (i-PrO)TiCl 3 as the Lewis acid gave pentacycle 28 as a major product (GC yield, 21 %; 10% isolated) along with the bicyclic ether 29 (13%) and backbone-rearranged bicyclic triene 30 (24%). The protic acid-catalyzed cyclization of tetramethylallyl alcohol 13 furnished fluoropentacycle 33 as the major product in 31 % yield. In contrast, the Lewis acid-catalyzed cyclization of 13 gave the dehydrofluorinated pentacycle 32 in 50% yield. Fluoropentacycle 33 was converted to sophoradiol (3), a biologically active pentacyclic triterpenoid of the oleanane series, by oxidative cleavage of the C3 isopropylidene and C22 vinylidene groups, regiospecific dehydrofluorination to introduce the C12–13 alkene, and finally stereoselective reduction of diketone 35. The conversion of 13 → 33 → 3 has demonstrated that the tetramethylallylic alchol group is an effective substitute for the epoxide (cf. 12 → 28) as an initiator of biomimetic polyene cyclizations. © 1994, American Chemical Society. All rights reserved.

  • cation stabilizing auxiliaries in polyene cyclizations 6 the fluorine atom as a cation stabilizing auxiliary in biomimetic polyene cyclizations 3 use to effect regiospecific control
    Journal of the American Chemical Society, 1993
    Co-Authors: William S Johnson, William R Bartlett, Fook S Tham, Robert A Buchanan, Rudolph K Kullnig
    Abstract:

    The fluorine atom substituted at the pro-C-13 position (steroid numbering) has been shown to be an effective cation-stabilizing (C-S) auxiliary in the acid-catalyzed cyclization of polyene substrates. The preparation of these Polyenes employed the known fragmentation of cyclic epoxy hydrazones to construct the methylacetylenic and gem-dimethyl groups. The fluoroolefinic ketal Claisen and cyclopropylcarbinol rearrangements established the 3(E) and 11 (E) trisubstituted alkenes

Rudolph K Kullnig - One of the best experts on this subject based on the ideXlab platform.

Jürgen Behnisch - One of the best experts on this subject based on the ideXlab platform.

  • Chemical dehydrochlorination of poly (vinyl chloride) by LiCl in dimethylformamide
    Polymer, 1992
    Co-Authors: A. Holländer, H Zimmermann, Jürgen Behnisch
    Abstract:

    Abstract The dehydrochlorination of poly (vinyl chloride) (PVC) with LiCl in dimethylformamide (DMF) is distinguished by the formation of polyenic products exhibiting an optical absorption peak at a wavelength greater than 500 nm. PVC dehydrochlorinated by other means usually absorbs below 450 nm. Since optical absorption characterizes the polyene sequence length distribution, we can assume that more Polyenes with a large number of conjugated double bonds are formed. Investigating the influence of reaction conditions on the formation of long conjugated Polyenes, a strong influence of reaction temperature and polymer concentration in the reaction system was found. Polyenes with an absorption peak at 630 nm could be prepared by adding an inert matrix polymer and hydrogen chloride. The mechanism of the formation of long polyene sequences is discussed by means of an ineffective Cl-Cl substitution, which changes the substituent configuration on the PVC backbone and thus creates steric opportunities for dehydrochlorination.

Mohammed H. Al-huniti - One of the best experts on this subject based on the ideXlab platform.

  • Palladium-Catalyzed Chemoselective Protodecarboxylation of Polyenoic Acids.
    Organic Letters, 2018
    Co-Authors: Mohammed H. Al-huniti, Mark A. Perez, Matthew K. Garr, Mitchell P. Croatt
    Abstract:

    Conditions for the first palladium-catalyzed chemoselective protodecarboxylation of polyenoic acids to give the desired Polyenes in good yields are presented. The reactions proceed under mild conditions using either a Pd(0) or Pd(II) catalyst and tolerate a variety of aryl and aliphatic substitutions. Unique aspects of the reaction include the requirement of phosphines, water, and a polyene adjacent to the carboxylic acid.

  • Palladium-Catalyzed Chemoselective Protodecarboxylation of Polyenoic Acids
    2018
    Co-Authors: Mohammed H. Al-huniti, Mark A. Perez, Matthew K. Garr, Mitchell P. Croatt
    Abstract:

    Conditions for the first palladium-catalyzed chemoselective protodecarboxylation of polyenoic acids to give the desired Polyenes in good yields are presented. The reactions proceed under mild conditions using either a Pd(0) or Pd­(II) catalyst and tolerate a variety of aryl and aliphatic substitutions. Unique aspects of the reaction include the requirement of phosphines, water, and a polyene adjacent to the carboxylic acid

Related terms

Polyenes - 15 days free trial to Access Experts & Abstracts