General, Divergent Platform for Diastereoselective Synthesis of trans-Cyclooctenes with High Reactivity and Favorable Physiochemical Properties

trans -Cyclooctenes (TCOs) are essential partners for the fastest known bioorthogonal reactions, but current synthetic methods are limited by poor diastereoselectivity.  Especially hard to access are hydrophilic TCOs with favorable physicochemical properties for live cell or in vivo experiments.  Described is a new class of TCOs, 'a-TCOs', that is prepared in high yield via stereocontrolled 1,2-additions of nucleophiles to trans-cyclooct-4-enone, which itself was prepared on large scale in two steps from 1,5-cyclooctadiene. Computational transition state models rationalize the diastereoselectivity of 1,2-additions to deliver a-TCO products, which were also shown to be more reactive than standard TCOs and less hydrophobic than even a trans -oxocene analog.  Illustrating the favorable physicochemical properties of a-TCOs, a fluorescent TAMRA derivative in live HeLa cells was shown to be cell-permeable through intracellular Diels-Alder chemistry and to washout more rapidly than other TCOs.