Tandem rearrangements

Three enantiomerically pure starting materials ensure remote stereochemical control Tandem iminium ion formation and vinyl silane cyclisation Part IV - Tandem Pericyclic Reactions Electrocyclic Formation of a Diene for Diels-Alder Reaction Tandem Ene Reactions Tandem [3,3]-Sigmatropic Rearrangements Tandem Aza-Diels-Alder and Aza-Ene Reactions... 

The hydroalkoxylation of alkynes has recently attracted some marked interest. Several groups have developed alkyne alkoxylation/Claisen rearrangement tandem processes using allylic alcohols as nucleophiles and NHC-Au complexes as the catalysts. The group of Nolan developed, in 2013, the hydrophenoxylation of alkynes by using a cooperative NHC-Au catalysis pro-cess. The hydroalkoxylation of allenes could also be performed. This reaction was shown to proceed in a regioselective manner with the alcohol being introduced on the least hindered terminal carbon of the allene. ... 

The most recent, and probably most elegant, process for the asymmetric synthesis of (+)-estrone appHes a tandem Claisen rearrangement and intramolecular ene-reaction (Eig. 23). StereochemicaHy pure (185) is synthesized from (2R)-l,2-0-isopropyhdene-3-butanone in an overall yield of 86% in four chemical steps. Heating a toluene solution of (185), enol ether (187), and 2,6-dimethylphenol to 180°C in a sealed tube for 60 h produces (190) in 76% yield after purification. Ozonolysis of (190) followed by base-catalyzed epimerization of the C8a-hydrogen to a C8P-hydrogen (again similar to conversion of (175) to (176)) produces (184) in 46% yield from (190). Aldehyde (184) was converted to 9,11-dehydroestrone methyl ether (177) as discussed above. The overall yield of 9,11-dehydroestrone methyl ether (177) was 17% in five steps from 6-methoxy-l-tetralone (186) and (185) (201). 

Cartion-cartxin bond formation via tandem Mannich condensation, cationic aza-Cope rearrangement of homoaHylarrunes, leading to pyrolidmes... 

Tandem reactions of heterocycles combining Diels-Alder reactions with sig-matropic rearrangements 98S227. 

Tandem reactions combining Diels-Alder reactions with sigmatropic rearrangements in syntheses of heterocycles 98S227. 

The Rh2(DOSP)4 catalysts (6b) of Davies have proven to be remarkably effective for highly enantioselective cydopropanation reactions of aryl- and vinyl-diazoacetates [2]. The discovery that enantiocontrol could be enhanced when reactions were performed in pentane [35] added advantages that could be attributed to the solvent-directed orientation of chiral attachments of the ligand carboxylates [59]. In addition to the synthesis of (+)-sertraline (1) [6], the uses of this methodology have been extended to the construction of cyclopropane amino acids (Eq. 3) [35], the synthesis of tricyclic systems such as 22 (Eq. 4) [60], and, as an example of tandem cyclopropanation-Cope rearrangement, an efficient asymmetric synthesis of epi-tremulane 23 (Eq. 5) [61]. 

Neuschuetz K., Velker J., Neier R. Tandem Reactions Combining Diels-Alder Reactions With Sigmatropic Rearrangement Processes and Their Use in Synthesis Synthesis 1998 227-255... 

Shi, F.-Q., Li, X., Xia, Y, Zhang, L. and Yu, Z.-X. (2007) DFT Study of the Mechanisms of In Water Au(I)-Catalyzed Tandem [3,3]-Rearrangement/Nazarov Reaction/[l,2]-Hydrogen Shift of Enynyl Acetates A Proton-Transport Catalysis Strategy in the Water-Catalyzed [l,2]-Hydrogen Shift. Journal of the American Chemical Society, 129, 15503-15512. 

Pinacol Rearrangement in Tandem with the Carbonyl-Ene Reaction. Overman and co-workers have developed protocols in which pinacol rearrangement... 

Chapter 10 considers the role of reactive intermediates—carbocations, carbenes, and radicals—in synthesis. The carbocation reactions covered include the carbonyl-ene reaction, polyolefin cyclization, and carbocation rearrangements. In the carbene section, addition (cyclopropanation) and insertion reactions are emphasized. Recent development of catalysts that provide both selectivity and enantioselectivity are discussed, and both intermolecular and intramolecular (cyclization) addition reactions of radicals are dealt with. The use of atom transfer steps and tandem sequences in synthesis is also illustrated. 

Allyl aryl ethers undergo accelerated Claisen and [1,3] rearrangements in the presence of a mixture of trialkylalanes and water or aluminoxanes. The addition of stoichiometric quantities of water accelerates both the trimethylaluminum-mediated aromatic Claisen reaction and the chiral zirconocene-catalyzed asymmetric carboalumination of terminal alkenes. These two reactions occur in tandem and, after oxidative quenching of the intermediate trialkylalane, result in the selective formation of two new C-C bonds and one C-0 bond (Eq. 12.70).153 Antibodies have also been developed to catalyze Claisen154 and oxy-Cope155 rearrangements. 

The mass spectra of azolides are not very specific, since they depend to a large extent on the structures of the respective acyl groups. Flash vacuum pyrolyses of azolides has been studied for 1-acyl-1,2,4-triazoles and benzotriazolides by tandem mass spectrometry (MS/MS). 461 Rearrangements of triazolides resulted in the formation of oxazoles. 471... 

Cairns N, Harwood LM, Astles DP (1994) Tandem thermal claisen-cope rearrangements of coumarate derivatives. Total syntheses of the naturally occurring coumarins suberosin, demethylsuberosin, ostruthin, balsamiferone and gravelliferone. J Chem Soc Perkin Trans... 

Tandem ammonium ylide generation-rearrangement reactions... 

Muroni et al. have reported a tandem metallocarbenoid/ylide/[l,2]-Stevens rearrangement <2004TA2609>. The azoniaspirocycle ylide 5 is formed by trapping of the metallocarbene precursor (Equation 14). Heating the ylide in toluene then gave indolizidinone 55 as a single diastereoisomer. 

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