Synlett

Herein, we report strain-driven regioselective tandem ring-opening cross-metathesis (ROCM) of a linearly fused cage system that contains both bicyclo[2.2.1]heptene and bicyclo[2.2.2]octene units fused to the same cage system. The synthesis of novel cage propellane involves Diels–Alder cycloaddition and [2+2] photocycloaddition as key steps.

Synlett 2022; 33: V-DOI: 10.1055/s-0042-1752341Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, GermanyArticle in Thieme eJournals:Table of contents

A simple protocol catalyzed by a Brønsted acid, trifluoromethanesulfonic acid (CF3SO3H), to synthesize conjugated diene-diones from easily accessible tertiary propargyl alcohols and 1,3-dicarbonyl compounds is described. Reactions are performed in an air atmosphere by using undried solvents with water being the environmentally benign side product of the process. Preliminary synthetic applications of the conjugated diene-diones in the formation of conjugated dieneones and furans are also reported herein.

We report a highly branch-selective and enantioselective allylic alkylation of simple ketones with racemic aliphatic allylic carbonates under mild conditions. By using a Rh–bisoxazolinephosphine system and catalytic amounts of a base in THF, a series of chiral β-branched γ,δ-unsaturated ketones were obtained with excellent regio- and enantioselectivities. An outer-sphere nucleophilic substitution C–C bond-formation process is proposed on the basis of mechanistic studies.

A rhodium(III)-catalyzed transfer hydrogenation of unsaturated ketones was developed. The simple catalytic system could be used for the 1,4-reduction of unsaturated cyclic, acyclic ketones, diketones, as well as β-ketoester, and a variety of functional groups were well-tolerated, affording products in moderate to excellent yields.

A synthetic strategy based on the application of three consecutive ring-expansion reactions has been used in the synthesis of analogues of the macrocyclic core of the solomonamide natural products. Starting from a simple, readily available tetrahydrocarbazole, oxidative ring expansion is followed by two further 3- and 4-atom ring-expansion reactions, enabling the insertion of amino acid and hydroxy acid derived linear fragments into 15- to 17-membered-ring-enlarged macrocyclic products.

We present a combined experimental and computational study on the thermodynamic stability of cis- and trans-alkenes substituted with dispersion energy donor (DED) groups. To investigate the role of noncovalent interactions on equilibrium of cis- and trans-alkenes we utilized hydrochlorination reactions. While the general assumption is that increasing steric bulk favors the trans-alkene, we observe an equilibrium shift towards the more crowded cis-alkene with increasing substituent size. With the aim to quantify noncovalent interactions, we performed a double mutant cycle to experimentally gauge the attractive potential of bulky substituents. Additionally, we utilized local energy decomposition analysis at the DLPNO-CCSD(T)/def2-TZVP level of theory. We found LD interactions and Pauli exchange repulsion to be the most dominant components to influence cis- and trans-alkene equilibria.

We report the effect of samarium complexation of a modified flavin entity in displaying efficient photocatalytic activity toward sulfoxidation reactions. Single-crystal X-ray diffraction studies were performed for the structural characterization of the photocatalyst. Spectroscopic and electrochemical studies were undertaken to better understand the nature of the complex when compared with the nonmetalated flavin moiety. The catalytic efficiency was maximal in 2:8 water–2,2,2-trifluoroethanol using 1 mol% of the catalyst in the presence of blue LED light under an oxygen atmosphere. Insignificant product formation was observed with the nonmetalated flavin moiety. A wide range of sulfides were used to explore the substrate scope.

Many natural products and biologically important complex organic scaffolds have convoluted structures around their core skeleton. Interestingly, with just changing the outskirts, the core reflects new and unique degrees of various physical and chemical properties. A very common but intriguing core is a five-membered ring horning heaps of organic molecules crafts. The power of [3+2] cycloaddition reactions to generate five-membered ring systems allocate chemists to envision synthetic procedures of wonder molecules and if it is facilitating a cascade sequence, then the end product will imbibe significant level of complexity having applications in medicinal and pharmaceutical fields. This Account highlights the broad interest in assembling recent advances in cascade reactions involving [3+2] cycloaddition as the power tool in order to conceive breakthrough organic architectures reported in the last ten years. We foresee that our comprehensive collection of astonishing [3+2] cycloaddition enabled cascades will provide valuable insights to polycyclic molecular construction and perseverant approach towards nonconventional synthetic procedures to the organic community.1 Introduction2 Synthesis of Oxindoles Skeleton3 Synthesis of Oxazoles Skeleton4 Synthesis of Oxadiazoles Skeleton5 Synthesis of Nitrogen-Containing Heterocycles6 Synthesis via Formal [3+2] Cycloaddition7 Synthesis of Miscellaneous Scaffolds8 Conclusion

A simple, mild, and metal-free cascade reaction has been developed for the construction of highly functionalized olefins. The approach relies on the initial formation of [3+2]-cycloadducts from a pyridinium ylide generated in situ from polymer-bound DMAP (PS-DMAP) with an N-substituted maleimide or an α,β-unsaturated β-keto ester. The cycloadduct decomposes to regenerate supported DMAP and yield a functionalized itaconimide or olefin. The method has a broad substrate scope. The alkene product has been further transformed into trisubstituted furan. PS-DMAP could be reused for five cycles.