Desymmetrization of 1,4‐Pentadien‐3‐ol by the Asymmetric 1,3‐Dipolar Cycloaddition of Azomethine Imines

Abstract

Desymmetrization of the divinyl carbinol, 1,4-pentadien-3-ol, was accomplished by the asymmetric 1,3-dipolar cycloaddition of azomethine imines based on a magnesium-mediated, multi-nucleating chiral reaction system utilizing diisopropyl (R,R)-tartrate as the chiral auxiliary. The corresponding optically active trans-pyrazolidines, each with three contiguous stereogenic centers, were obtained with excellent regio-, diastereo-, and enantioselectivity, with results as high as 99% ee. This reaction was shown to be applicable to both aryl-and aliphatic-substituted azomethine imines. The use of a catalytic amount of diisopropyl (R,R)-tartrate was also effective when accompanied by the addition of MgBr 2 .

AMHB: (Anti)aromaticity-Modulated Hydrogen Bonding

“…A survey of the online Cambridge Structural Database (WebCSD), in which H-bond-donor/-acceptor distances were compared, found that the average distance for 2a in five crystals of its derivatives − is 0.147 Å shorter (2.703(2) vs 2.850(4) Å, see Figure a) than for 2a ′ in 12 crystal structures. − Conversely, the average N···N distance in 3a derivatives in three crystal structures − is 0.110 Å longer (3.013(3) vs 2.903(3), see Figure b) than 3a ′ derivatives in five crystal structures. − These observations offer strong experimental support for the notion of aromaticity assisted H-bonding and aromaticity disrupted H-bonding in the cases of 2a and 3a , respectively.…”

Facile assembly of 1,5-diazocan-2-ones via cyclization of tethered sulfonamides to cyclopropenes

“…General information NMR spectra were recorded on a Bruker Avance DRX-500 (500 MHz) with a dual carbon/proton cryoprobe (CPDUL). 13 C NMR spectra were registered with broadband decoupling. The (+) and (À) designations represent positive and negative intensities of signals in 13 C DEPT-135 experiments.…”

“…5,6 It is known that medium-sized 8-membered rings are difficult to assemble via conventional methods of cyclization, 7 largely due to the enthalpic cost incurred in the transition state as well as the decreased entropy of the cyclic products relative to their linear precursors. 8 Several alternative synthetic approaches to the eight-membered 1,5-diazocin-2-one core have been developed, including Beckman rearrangement, 9 fragmentation of 1,5-diazabicyclo[3.3.1]nonan-2-ones, 10 reductive N-N scission of tetrahydro-1H,5H-pyrazolo[1,2-a]pyrazol-1-ones, [11][12][13][14] as well as various ring closures, exploiting intramolecular versions of reductive amination, [15][16][17][18] amine acylation, 7,[19][20][21][22] strain release-driven transamidation, [23][24][25] and S N Ar reactions. 26 Herein, we disclose a new application of metal-templated intramolecular 8-exo-trig cyclization involving nucleophilic addition of sulfonamides tethered to a cyclopropene moiety.…”

Magnesium Catalysis in Asymmetric Synthesis

“…In-Situ-Generated Magnesium Catalytic Methods with Non-covalent Additives cyclization process, which generated three stereocenters with high diastereoselectivity (Scheme 50). 99,100 In addition to the careful design of poly-acid ligands and the rational selection of magnesium sources for the formation of multimetal center Mg(II) catalysts, in-situformed multinuclear magnesium catalysts may also be obtained from monometal/ligand species. As mentioned above, nonlinear effects were often observed in asymmetric reactions catalyzed by in-situ-formed magnesium complexes.…”