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Covering: January 2000 to July 2018 gem-Dimethylcyclobutanes are a common motif found in a multitude of natural products, and thus these structures have captivated synthetic chemists for years. However, until the turn of the century, most synthetic efforts relied upon the use of widely available terpenes, such as pinene or caryophyllene, that already contain the gem-dimethylcyclobutane motif. This approach limits the scope of molecules that can be accessed readily. This review highlights recent syntheses in which the gem-dimethylcyclobutane is assembled via de novo approaches. An outlook on the future of this research area is also provided. [ABSTRACT FROM AUTHOR]

The application of thioallenoates to catalytic enantioselective [2+2]-cycloadditions with unactivated alkenes is reported. In many cases, the thioallenoates examined exhibit superior reactivity and selectivity compared to the allenic esters generally used in these cycloadditions. Image 1 [ABSTRACT FROM AUTHOR]

Abstract: The first synthesis of hebelophyllene E is presented, along with assignment of its previously unknown relative configuration through synthesis of epi‐ent‐hebelophyllene E. Development of a catalytic enantioselective [2+2] cycloaddition of alkenes and allenoates provides access to the required chiral geminal dimethylcyclobutanes. Key to its success is the identification of a novel oxazaborolidine catalyst which promotes the cycloaddition in high enantioselectivities with good functional‐group tolerance (9 examples, up to 97:3 e.r.). Thus, a late‐stage cycloaddition using a fully functionalized alkene, followed by a diastereoselective reduction allows a concise entry to this class of natural products. [ABSTRACT FROM AUTHOR]

The title compounds were prepared in a two-step sequence from 4,4-dimethoxybutyronitrile and the respective esters by Claisen condensation and subsequent Paal-Knorr pyrrole synthesis. The sequence could be performed as a one-pot procedure delivering the pyrroles in yields of 47-72% over two steps (13 examples). Intramolecular variants of the method were applied to the total synthesis of danaidal and suffrutine A from the respective trityl-protected ω-amino alkanoates. [ABSTRACT FROM AUTHOR]

Pyrrole has been employed for the first time as a directing group in the Pd(II)-catalyzed ortho-functionalization of C(sp2)-H bonds. A variety of substituted 2-phenylpyrroles were successfully methylated, alkylated, or benzylated in the ortho-position of the benzene ring, yielding the respective 2-substituted pyrrol-2-yl benzenes (36 examples, 51-93% yield). Neither additives nor additional ligands were required to perform the reaction, which was routinely conducted with PdBr2 as the catalyst and Li2CO3 as the base. Mechanistically, there is evidence that precoordination of palladium to the pyrrole enables the regioselective ortho-attack. [ABSTRACT FROM AUTHOR]

Elegant desymmetrization strategies have been established for 3-substituted, 3,3 as well as 2,2-disubstituted oxetanes, which give rise to a diversity of products. Keywords: asymmetric synthesis; desymmetrization; oxetane; oxygen heterocycles; strained molecules EN asymmetric synthesis desymmetrization oxetane oxygen heterocycles strained molecules 1 1 1 04/05/21 20210401 NES 210401 B The synthetic utility of prochiral oxetanes b , based on their inherent ring-strain and Lewis-basicity, is highlighted in the Minireview by A. Sandvoß and J. M. Wiest on page 5871. Asymmetric synthesis, desymmetrization, oxetane, oxygen heterocycles, strained molecules. [Extracted from the article]

Strain relief of oxetanes offers a plethora of opportunities for the synthesis of chiral alcohols and ethers. In this context, enantioselective desymmetrization has been identified as a powerful tool to construct molecular complexity and this has led to the development of elegant strategies on the basis of transition metal, Lewis acid, and Brønsted acid catalysis. This review highlights recent examples that harness the inherent reactivity of prochiral oxetanes and offers an outlook on the immense possibilities for synthetic application., (© 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Control over the photochemical outcome of photochromic molecules in solution represents a major challenge, as photoexcitation often leads to multiple competing photochemical and/or supramolecular pathways resulting in complex product mixtures. Herein, we demonstrate precise and efficient control over the photochemical behaviour of cyanostilbenes in solution using a straightforward solvent-controlled approach based on supramolecular polymerization. To this end, we designed a π-extended cyanostilbene bolaamphiphile that exhibits tuneable solvent-dependent photochemical behaviour. Photoirradiation of the system in a monomeric state (in organic solvents) exclusively leads to a highly reversible and efficient E / Z photoisomerization, whereas a nearly quantitative [2 + 2] photocycloaddition into a single cyclobutane ( anti head-to-tail) occurs in aqueous solutions. These results can be rationalized by a highly regular and preorganized antiparallel J-type arrangement of the cyanostilbene units that is driven by aqueous supramolecular polymerization. The presented concept demonstrates a novel approach towards solvent-selective and environmentally friendly photochemical transformations, which is expected to broaden the scope of supramolecular polymerization., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)