Search results for "REARRANGEMENT"
showing 10 items of 298 documents
New approaches to the synthesis of organofluorine nitrogenated derivatives
2004
Fluorinated carboxylic acids are valuable building blocks for several types of organofluorine nitrogenated derivatives. In this review paper, several strategies that use these compounds as starting materials are described. First, fluorinated seven-membered cyclic β-amino esters can be diastereoselectively synthesized from these compounds with a ring-closing metathesis (RCM) reaction as the key step. The use of the RCM reaction in a different approach enables the preparation of fluorinated cyclic α-amino acid derivatives. Fluorinated carboxylic acids also constitute the starting material for the asymmetric synthesis of fluorinated allylic amines. Finally, a solution and solid-phase synthesis…
Enediolates and dienediolates of carboxylic acids in synthesis. Synthesis of β,γ-epoxyacids from α-chloroketones
1998
Abstract Lithium dienolates of saturated or α,β-unsaturated acids react with α-chloroketones provide a convenient method for preparation of highly sustituted β,γ-epoxyacids. These highly reactive compounds lead in most cases to variable ammounts of the corresponding β-lactones and allylic alcohols.
Unsaturated syn- and anti-1,2-Amino Alcohols by Cyclization of Allylic Bis-trichloroacetimidates. Stereoselectivity Dependence on Substrate Configura…
2014
Disubstituted allylic bis-imidates undergo Lewis acid catalyzed or spontaneous cyclization to oxazolines, which are precursors of unsaturated amino alcohols. Stereoselectivity of the cyclization is mainly determined by the substrate configuration. Highly selective cis-oxazoline formation is achieved starting from anti-E-bis-imidates while trans-oxazoline predominantly forms from anti-Z-bis-imidates. On the basis of DFT calculations, the stereoselectivity trends can be explained by the formation of the energetically most stable carbenium ion conformation, followed by the cyclization via most favorable bond rotations.
Diastereoselective synthesis of antiquorin and related polyoxygenated atisene-type diterpenes
2007
Abstract A diastereoselective approach to polyoxygenated atisene-type diterpenes starting from (S)-(+)-carvone is described. The key steps used in the preparation of the atisene framework are an intramolecular Diels–Alder reaction, an intramolecular diazoketone cyclopropanation, an endocyclic cyclopropane ring cleavage and the regioselective reduction of an allylic bromide by a low-valent chromium species. The synthesis of natural atisanes antiquorin (1), atis-16-ene-3,14-dione (3), atis-16-ene-2,3,14-trione (8) and 3β-hydroxy-atis-16-ene-2,14-dione (9) following this approach is presented. Also described is the synthesis of 18-hydroxy-atis-16-ene-3,14-dione (5), the structure erroneously a…
A Green Look at the Aldol Reaction
2005
Aldol reactions have been and are widely applied for the preparation of β-hydroxy aldehydes, β-hydroxy ketones or α,β-unsaturated aldehydes or ketones through addition or addition-elimination reactions of aldehydes and ketones. The study of the aldol reaction from the point of view of its greenness must have in mind first of all that a general synthetic method must be based on complete and efficient conversions of well defined selectivity and that greenness is more a term for comparison than an absolute kind of qualification. This comparison, when referred to the aldol reaction, applies here to the diverse modifications of the reaction. Thus, the original poorly selective, but highly atom e…
Design, Synthesis, and Biological Evaluation of Novel Fluorinated Ethanolamines
2011
The preparation of novel fluorinated allylamines and their use as key fragments for the stereoselective synthesis of hydroxyethyl secondary amine (HEA)-type peptidomimetics is described. Our strategy employs chiral sulfinyl imines as synthesis intermediates, by treatment of hemiaminal precursors with two equivalents of vinylmagnesium bromide. The subsequent oxidation of the allylic amines to the corresponding epoxides was achieved by treatment with methyl(trifluoromethyl)dioxirane. Finally, epoxide ring opening with a range of nitrogen nucleophiles provided a library of HEA-derived peptidomimetics with a phenyldifluoromethylene moiety. The biological evaluation of these derivatives revealed…
Novel Approach for Asymmetric Synthesis of Fluorinated β-Amino Sulfones and Allylic Amines
2003
[reaction: see text] Enantiomerically pure gamma-fluoroalkyl beta-amino sulfones are readily synthesized in three steps starting from fluorinated imidoyl chlorides and arylmethyl sulfones. A complementary two-step sequence starting from chiral fluorinated beta-amino sulfoxides has also been developed. To illustrate the application of this procedure, a new method for the synthesis of alpha-fluoroalkyl allylic amines in optically pure form involving a Julia methylenation-desulfonylation reaction is presented.
Investigation of the aqueous transmetalation of π-allylpalladium with indium salt: the use of the Pd(OAc)2–TPPTS catalyst
2005
pi-Allylpalladium complexes could be generated in water by the palladium(0) water soluble catalyst prepared in situ from palladium acetate and TPPTS. These complexes were transmetalated with indium to react with benzaldehyde. The aqueous solution of Pd(0)(TPPTS)(n) could be reused without deterioration of the catalyst in the first and second recycling. The system proved to be efficient with primary and secondary allylic substrates. The stereochemical outcome of the allylation through umpolung of allylpalladium, was also studied using models with a restraint conformation.
Synthesis of borylindenides. Complexes with iron and rhenium moieties
1999
Abstract Borylation of lithium indenide with BBrMe 2 gives the allylic 1-indenyl derivative (1-Ind)BMe 2 ( 1c ) together with the bis-allylic connected species (1-Ind) 2 BMe ( 3 ) and with BCl i Pr 2 , the allylic 1-indenyl (1-Ind)B i Pr 2 ( 1d ); the latter, with Et 3 N or Py added, rearranges to the vinylic 3-indenyl isomer (3-Ind)B i Pr 2 ( 2d ). The disubstituted indene C 9 H 6 Ind(SiMe 3 )B(O 2 C 2 Me 4 ) ( 5 ) was prepared from Li[C 9 H 6 B(O 2 C 2 Me 4 )] ( 4b ) and Me 3 SiCl. Both (1-Ind)BMe 2 and (1-Ind)B i Pr 2 readily undergo metalation when treated with LiTMP or LiInd to give pure 1-borylindenides Li(C 9 H 6 BMe 2 ) ( 4c ) and Li(C 9 H 6 B i Pr 2 ) ( 4d ). A barrier to internal …
Synthesis of borylindenides; structure of [Li(N,N′,N″-Me3-1,3,5-C3H6N3)][1-C9H6{B(NMe2)2}]
1998
Abstract Borylation of lithium indenide (LiInd) affords indenylboranes. With BCl(NMe2)2 the primary allylic 1-indenyl derivative IndB(NMe2)2 (1) readily rearranges to the more stable vinylic bis(dimethylamino)(3-indenyl)borane 1′. With BCl(OCMe2)2 the (1-indenyl)-1,3,2-dioxaborolane IndB(OCMe2)2 (2) is obtained. Both indenylboranes 1′ and 2 readily undergo metalation when treated with lithium amides such as LiTMP or LDA to give 1-borylindenides Li[C9H6B(NMe2)2] [Li(3)] and Li[C9H6B(OCMe2)2] [Li(5)] in high yields. In the systems 1′/LiInd and 2/LiInd metalation equilibria are established with equlibrium constants K≈1 (1'/LiInd) and K≈1.4 (2/LiInd). The structure of the solvate [Li(TMHT)][1-C…