Synthesis of (−)-Cytisine Using a 6-endo aza-Michael Addition

Syntheses, crystal structures and Hirshfeld surface analyses of N-aryl-sulfonyl derivatives of cytisine

By aryl-sulfonyl-ation of cytisine in the presence of tri-ethyl-amine, three new compounds have been obtained in good yields: (7R,9R)-N-[(4-ethyl-phen-yl)sulfon-yl]cytisine, C19H22N2O3S (I) {systematic name: (1R,5R)-3-[(4-ethyl-phen-yl)sulfon-yl]-1,2,3,4,5,6-hexa-hydro-8H-1,5-methano-pyrido[1,2-a][1,5]diazo-cin-8-one}, (7R,9R)-N-[(4-chloro-phen-yl)sulfon-yl]cytisine, C17H17ClN2O3S (II) {systematic name: (1R,5R)-3-[(4-chloro-phen-yl)sulfon-yl]-1,2,3,4,5,6-hexa-hydro-8H-1,5-methano-pyrido[1,2-a][1,5]diazo-cin-8-one} and (7R,9R)-N-[(3-nitro-phen-yl)sulfon-yl]cytisine, C17H17N3O5S (III) {systematic name: (1R,5R)-3-[(3-nitro-phen-yl)sulfon-yl]-1,2,3,4,5,6-hexa-hydro-8H-1,5-methano-pyrido[1,2-a][1,5]diazo-cin-8-one}. The crystal structures of the compounds were determined on the basis of single-crystal X-ray diffraction data. The crystal structures of (I)-(III) are distinguished by the arrangement of two fragments of the mol-ecule around the sulfonyl site. For all structures, weak C-H⋯O hydrogen bonds are developed. Hirshfeld surface analysis shows that H⋯H (for I and II) and H⋯O/O⋯H (for III) inter-actions make the most important contribution to the crystal packing.

Two Decades of Progress in the Asymmetric Intramolecular aza-Michael Reaction

The asymmetric intramolecular aza-Michael reaction (IMAMR) is a very convenient strategy for the generation of heterocycles bearing nitrogen-substituted stereocenters. Due to the ubiquitous presence of these skeletons in natural products, the IMAMR has found widespread applications in the total synthesis of alkaloids and biologically relevant compounds. The development of asymmetric versions of the IMAMR are quite recent, most of them reported in this century. The fundamental advances in this field involve the use of organocatalysts. Chiral imidazolidinones, diaryl prolinol derivatives, Cinchone-derived primary amines and quaternary ammonium salts, and BINOL-derived phosphoric acids account for the success of those methodologies. Moreover, the use of N-sulfinyl imines with a dual role, as nitrogen nucleophiles and as chiral auxiliaries, appeared as a versatile mode of performing the asymmetric IMAMR.

Characterising Supramolecular Architectures in Crystals Featuring I⋯Br Halogen Bonding: Persistence of X⋯X’ Secondary-Bonding in Their Congeners

The Cambridge Structural Database was surveyed for crystals featuring I⋯Br secondary-bonding in their supramolecular assemblies occurring independently of other obvious supramolecular synthons and devoid of other halogen bonding interactions. In all, 41 crystals satisfied these criteria, with nine examples of zero-dimensional aggregation (uniformly two-molecule aggregates) and 30 one-dimensional chains of varying topology (linear, zigzag and helical). There is one example each of two- and three-dimensional patterns. Type-I, type-II and intermediate bonding situations are apparent; for type-II bonding, the ratio of iodide:bromide functioning as the electrophile is 2:1. Most molecules participated, on average, in one I⋯Br contact, although smaller numbers of half (zero-dimensional) or two contacts (two- and three-dimensional) were observed. The propensity of the formation of related halogen bonding interactions in congeners of the 41 investigated crystals was also studied. Congeners were apparent for 11 crystals, with seven of these exhibiting isostructural relationships, in terms of space-group symmetry and unit-cell parameters. Isostructural relationships do not ensure the formation of analogous aggregation patterns, particularly and in accord with expectation, for the lighter halides. When formed, often distinct aggregation patterns are observed despite the isostructural relationships. Hetero-atomic halogen bonding offers surprises and opportunities in crystal engineering endeavours.

The endo-aza-Michael addition in the synthesis of piperidines and pyrrolidines

Intramolecular endo-aza-Michael additions are categorised in various ways.

CF-Targeter: A Rational Biological Cell Factory Targeting Platform for Biosynthetic Target Chemicals

Biosynthesis is a promising method for chemical synthesis. However, due to varieties between different microorganism hosts, yield and heterologous pathways needed for production of target chemical may also vary from different strains. One of the main challenges in metabolic engineering is to select an appropriate chassis host for specified target chemical production. However, with thousands of microorganisms existing in nature and extremely complicated metabolism within them, it is still time-consuming and error-prone work to achieve such a goal only through experimental methods, even with some existing computational methods. Hence, more efficient methods should be proposed to assist in selecting appropriate chassis hosts. In this article, based on symbolic reaction repositories and a pathway search algorithm which performed 1 400 000 searches for per target compound, we established a biological reasoning system for appropriate chassis host selection by coupling with various GEM-models. By using a supercomputer to calculate the biosynthetic pathways for more than 1 month, nearly 50 000 000 biosynthetic pathways are computed for production of 6026 compounds within 70 microorganisms. With retrieved organisms for specified target production, several heterologous biosynthetic pathways can be shown in length order, and then the maximum theoretical yields and thermodynamic feasibility can be calculated in real time under customized growth conditions and physiological states. From the computation results, the system not only identifies experimentally validated pathways but also outputs more efficient solutions with less heterologous steps or higher maximum possible theoretical yield by engineering other organism hosts. CF-targeter is available at http://www.rxnfinder.org/cf_targeter/.

Phosphite-Catalyzed C-H Allylation of Azaarenes via an Enantioselective [2,3]-Aza-Wittig Rearrangement

A phosphite-mediated [2,3]-aza-Wittig rearrangement has been developed for the regio- and enantioselective allylic alkylation of six-membered heteroaromatic compounds (azaarenes). The nucleophilic phosphite adducts of N-allyl salts undergo a stereoselective base-mediated aza-Wittig rearrangement and dissociation of the chiral phosphite for overall C-H functionalization of azaarenes. This method provides efficient access to tertiary and quaternary chiral centers in isoquinoline, quinoline, and pyridine systems, tolerating a broad variety of substituents on both the allyl part and azaarenes. Catalysis with chiral phosphites is also demonstrated with synthetically useful yields and enantioselectivities.

The logic of translating chemical knowledge into machine-processable forms: a modern playground for physical-organic chemistry

With renewed interest and significant progress in computer-assisted synthetic planning, it is essential to codify the logic that should be followed when translating organic synthetic knowledge into reaction rules understandable to the machine.