An Untethered and Formal Intermolecular Hexadehydro-Diels-Alder Reaction: Alkynylboronates with 2-(1,3-Butadiynyl)pyridines.

We show that 2-diynylpyridine and a Bpin-terminated monoyne or diyne will cross-react to form benzyne intermediates. These reactive intermediates are captured by various in situ trapping agents to give products of three-component reactions. Various control reactions, substrate modification, binding studies, and DFT analysis suggest that a small amount of a noncovalent Lewis acid-base complex is the active species within which the diyne and diynophile engage to produce the benzyne.

Alkynes to (Free) Carbenes to Polycyclic Cyclopropanes.

Carbenes and carbenoids are commonly employed for the synthesis of cyclopropane-containing compounds. Here we report the metal-free, intramolecular cyclopropanation of tethered alkenes by free carbenes derived from alkynes to construct structurally unique multicyclic cyclopropanes with perfect atom economy. The nature of the tether influences both the rate of carbene formation and subsequent competing reaction events.

Trap colour strongly affects the ability of deep learning models to recognize insect species in images of sticky traps.

Background: The use of computer vision and deep learning models to automatically classify insect species on sticky traps has proven to be a cost- and time-efficient approach to pest monitoring. As different species are attracted to different colours, the variety of sticky trap colours poses a challenge to the performance of the models. However, the effectiveness of deep learning in classifying pests on different coloured sticky traps has not yet been sufficiently explored.

Reactions of Electrophilic Allenoates [and Isocyanates/Isothiocyanates] with a 2-Alkynylpyridine via a Free Carbene Intermediate.

A pyridine containing a 2-alkynyl substituent armed with a carbene reporter group [R = C(Me)OAc] is shown to engage electrophilic allenes to generate intermediate free carbenes. Depending on the electron density at the carbene carbon atom, a feature that is modulated by the substituents on the allene substrate, the carbene will either rearrange or eject an acetate leaving group, leading to various types of indolizine-containing products. Iso(thio)cyanates react in an analogous fashion.

Relative Rates of Transesterification vis-à-vis Newman's Rule of Six.

The relative reactivity of a systematic series of simple aliphatic acetate esters has been measured. Exposure of pairs of esters of increasing remote steric hindrance (by altering the degree of branching of the ester alkyl group) to a methanolic solution of CsCO proved to be a reliable (and general) method for quantitating the rate differences in these base-catalyzed transesterification reactions. The trends in relative rates are in accordance with the qualitative "Rule of Six" put forward by Melvin S.