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Fabrics—materials consisting of layers of woven fibres—are some of the most important materials in everyday life1. Previous nanoscale weaves2–16 include isotropic crystalline covalent organic frameworks12–14 that feature rigid helical strands interlaced in all three dimensions, rather than the two-dimensional17,18 layers of flexible woven strands that give conventional textiles their characteristic flexibility, thinness, anisotropic strength and porosity. A supramolecular two-dimensional kagome weave15 and a single-layer, surface-supported, interwoven two-dimensional polymer16 have also been reported. The direct, bottom-up assembly of molecular building blocks into linear organic polymer chains woven in two dimensions has been proposed on a number of occasions19–23, but has not previously been achieved. Here we demonstrate that by using an anion and metal ion template, woven molecular ‘tiles’ can be tessellated into a material consisting of alternating aliphatic and aromatic segmented polymer strands, interwoven within discrete layers. Connections between slowly precipitating pre-woven grids, followed by the removal of the ion template, result in a wholly organic molecular material that forms as stacks and clusters of thin sheets—each sheet up to hundreds of micrometres long and wide but only about four nanometres thick—in which warp and weft single-chain polymer strands remain associated through periodic mechanical entanglements within each sheet. Atomic force microscopy and scanning electron microscopy show clusters and, occasionally, isolated individual sheets that, following demetallation, have slid apart from others with which they were stacked during the tessellation and polymerization process. The layered two-dimensional molecularly woven material has long-range order, is birefringent, is twice as stiff as the constituent linear polymer, and delaminates and tears along well-defined lines in the manner of a macroscopic textile. When incorporated into a polymer-supported membrane, it acts as a net, slowing the passage of large ions while letting smaller ions through. An anion and metal ion template is used to form woven polymer patches that are joined together by polymerization into a fully woven, two-dimensional, molecular patchwork.

This account describes the discovery and development of mild and efficient protocols for the generation of highly reactive nitroso compounds to allow their subsequent use in previously inaccessible or challenging chemistries. 1 Introduction 2 Formation of Nitrosocarbonyl Compounds 3 The Nitrosocarbonyl Ene Reaction 3.1 Single-Pot Nitrosocarbonyl Ene Reactions 3.2 Copper-Catalyzed Aerobic Oxidation for the Nitroso­carbonyl Ene Reaction 4 The Hetero-Diels–Alder Reaction as a Platform for Studying Aerobic Oxidation 5 Dual Catalysis and α-Functionalization Reactions 5.1 α-Amination Reaction of β-Keto Esters 5.2 α-Oxygenation Reaction of β-Keto Esters 6 The Future of Nitroso Chemistry

The observed rate of reaction in the dysprosium triflate catalyzed aza-Piancatelli rearrangement is controlled by a key off-cycle binding between aniline and catalyst. Deconvoluting the role of these ancillary species greatly broadens our understanding of factors affecting the productive catalytic pathway. We demonstrate that the rate of reaction is controlled by initial competitive binding between the furylcarbinol and nitrogen nucleophile using either a Brønsted or Lewis acid catalyst and that the resulting rearrangement proceeds without involving the Brønsted and Lewis acid catalyst. This shows conclusively that the rate-controlling step and selectivity of reaction are decoupled. © 2013 American Chemical Society.

A molecular rearrangement of 5,5-spirocyclic cyclopentenones to 5,6-fused cyclopentenones catalyzed by Amberlyst®15 is described. This work emphasizes the utility of renewable resources, such as furfural, that can be transformed into a variety of valuable products. It also highlights the viability of 5,5-spirocycles as intermediates en route to 5,6-fused cyclopentenones. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

It has been convincingly argued that molecular machines that manipulate individual atoms, or highly reactive clusters of atoms, with Angstrom precision are unlikely to be realized. However, biological molecular machines routinely position rather less reactive substrates in order to direct chemical reaction sequences, from sequence-specific synthesis by the ribosome to polyketide synthases, where tethered molecules are passed from active site to active site in multi-enzyme complexes. Artificial molecular machines have been developed for tasks that include sequence-specific oligomer synthesis and the switching of product chirality, a photo-responsive host molecule has been described that is able to mechanically twist a bound molecular guest, and molecular fragments have been selectively transported in either direction between sites on a molecular platform through a ratchet mechanism. Here we detail an artificial molecular machine that moves a substrate between different activating sites to achieve different product outcomes from chemical synthesis. This molecular robot can be programmed to stereoselectively produce, in a sequential one-pot operation, an excess of any one of four possible diastereoisomers from the addition of a thiol and an alkene to an α,β-unsaturated aldehyde in a tandem reaction process. The stereodivergent synthesis includes diastereoisomers that cannot be selectively synthesized through conventional iminium-enamine organocatalysis. We anticipate that future generations of programmable molecular machines may have significant roles in chemical synthesis and molecular manufacturing.

The first example of a Piancatelli rearrangement of alcohols is demonstrated utilizing dysprosium(III) triflate as a catalyst to access oxaspirocycles in a highly diastereoselective manner. The cascade reaction constructs the spirocyclic ether ring system and the tertiary stereocenter in a single operation and is experimentally easy to perform.

This article describes the aza-Piancatelli rearrangement with hydroxylamines to 4-aminocyclopentenones and subsequent transformations that highlight the versatility of the cyclopentene scaffold and the value of the hydroxylamine nucleophile in this transformation.

Photoredox catalysis is employed to generate highly reactive acylnitroso species from hydroxamic acid derivatives. The conditions are shown to be comparable to a previously developed transition metal aerobic oxidation and are amenable to a range of transformations including Diels–Alder and ene reactions. This unique application of such an approach gives access to temporal and spatial control in nitroso chemistry.

© The Royal Society of Chemistry 2015. This article describes the aza-Piancatelli rearrangement with hydroxylamines to 4-aminocyclopentenones and subsequent transformations that highlight the versatility of the cyclopentene scaffold and the value of the hydroxylamine nucleophile in this transformation.

Photoredox catalysis is employed to generate highly reactive acylnitroso species from hydroxamic acid derivatives. The conditions are shown to be comparable to a previously developed transition metal aerobic oxidation and are amenable to a range of transformations including Diels–Alder and ene reactions. This unique application of such an approach gives access to temporal and spatial control in nitroso chemistry.

4-Hydroxycyclopentenones represent a privileged scaffold in chemical synthesis. A dysprosium(III) trifluoromethanesulfonate catalyzed rearrangement of furylcarbinols to 4-hydroxycyclopentenones via a 4π electrocyclization has been developed. The catalytic Piancatelli rearrangement affords a single trans-diastereomer from both aryl and alkyl substituted furylcarbinols.

4-Hydroxycyclopentenones represent a privileged scaffold in chemical synthesis. A dysprosium(III) trifluoromethanesulfonate catalyzed rearrangement of furylcarbinols to 4-hydroxycyclopentenones via a 4π electrocyclization has been developed. The catalytic Piancatelli rearrangement affords a single trans-diastereomer from both aryl and alkyl substituted furylcarbinols.

The acid-catalyzed rearrangement of furylcarbinols is utilized to access 4,5-substituted cyclopentenones. This cascade transformation began with implementing anilines, as an alternative nucleophile to water as used in the Piancatelli rearrangement, and has currently progressed through an intramolecular rearrangement to the use of alcohols as the nucleophile.

5,5-Spirocyclic cyclopentenones undergo Amberlyst-15-catalyzed ring opening/ring closure rearrangement to form tetrahydropyrans (II) and (IV).

A copper-catalyzed aminooxylation of β-ketoesters using transient nitrosoformate intermediates is reported. The transformation is highly practical, efficient and highlights the ambident reactivity of nitrosocarbonyl compounds through a rare example of a nitrosocarbonyl aldol reaction. Along with a broad substrate scope, the reaction conditions that help control the regiochemistry are explored and the use of N-carbamate protected hydroxylamine is showcased by subsequent one-pot annulation reactions.

The acid-catalyzed rearrangement of furylcarbinols is utilized to access 4,5-substituted cyclopentenones. This cascade transformation began with implementing anilines, as an alternative nucleophile to water as used in the Piancatelli rearrangement, and has currently progressed through an intramolecular rearrangement to the use of alcohols as the nucleophile. © Georg Thieme Verlag Stuttgart · New York.

A copper-catalyzed aminooxylation of β-ketoesters using transient nitrosoformate intermediates is reported. The transformation is highly practical, efficient and highlights the ambident reactivity of nitrosocarbonyl compounds through a rare example of a nitrosocarbonyl aldol reaction. Along with a broad substrate scope, the reaction conditions that help control the regiochemistry are explored and the use of N-carbamate protected hydroxylamine is showcased by subsequent one-pot annulation reactions. © 2013 The Royal Society of Chemistry.

The first example of a Piancatelli rearrangement of alcohols is demonstrated utilizing dysprosium(III) triflate as a catalyst to access oxaspirocycles in a highly diastereoselective manner. The cascade reaction constructs the spirocyclic ether ring system and the tertiary stereocenter in a single operation and is experimentally easy to perform.

Two complementary approaches are presented for the synthesis of the quinone chromophores of the naphthoquinone ansamycins and related natural products. The first involves the use of an improved protocol for the manganese(III) acetate mediated cyclization of 5-aryl-1,3-dicarbonyl compounds to β-naphthols, leading to the simple, scalable preparation of building blocks suitable for the synthesis of naturally occurring aminonaphthoquinones. The second approach involves the Diels–Alder reaction of a series of new, ester-containing Danishefsky-type dienes with N-protected aminobenzoquinones to allow more expeditious access to similar intermediates.