Stereocontrolled Microwave-Assisted Domino [3,3]-Sigmatropic Reactions: A Winstein-Overman Rearrangement for the Formation of Differentiated Contiguous C-N Bonds

Spot the difference in reactivity: a comprehensive review of site-selective multicomponent conjugation exploiting multi-azide compounds

Going beyond the conventional approach of pairwise conjugation between two molecules, the integration of multiple components onto a central scaffold molecule is essential for the development of high-performance molecular materials with multifunctionality. This approach also facilitates the creation of functionalized molecular probes applicable in diverse fields ranging from pharmaceuticals to polymeric materials. Among the various click functional groups, the azido group stands out as a representative click functional group due to its steric compactness, high reactivity, handling stability, and easy accessibility in the context of multi-azide scaffolds. However, the azido groups in multi-azide scaffolds have not been well exploited for site-specific use in molecular conjugation. In fact, multi-azide compounds have been well used to conjugate to the same multiple fragments. To circumvent problems of promiscuous and random coupling of multiple different fragments to multiple azido positions, it is imperative to distinguish specific azido positions and use them orthogonally for molecular conjugation. This review outlines methods and strategies to exploit specific azide positions for molecular conjugation in the presence of multiple azido groups. Illustrative examples covering di-, tri- and tetraazide click scaffolds are included.

Stereocontrol in an intermolecular Schmidt reaction of equilibrating hydroxyalkyl allylic azides

A selective intermolecular Schmidt reaction of equilibrating hydroxyalkyl allylic azides is reported to afford N-hydroxyalk-1-en-3-yl lactams in modest to high yields. For prochiral and chiral ketones, modest to high 1,5-diastereoselectivity was achieved, and the mechanistic analysis is supported by DFT calculation.

Divergent access to a novel 3,4-diaminophytosphingosine-like ceramide via sequential Overman rearrangement

A straightforward approach to a novel phytosphingosine-like ceramide has been accomplished. The cornerstone features of this divergent synthesis are a cascade Overman rearrangement of tris(imidate) to introduce three desired stereogenic centres via sequential chirality transfer and an effective olefin cross-metathesis to install a long side chain. The final unusual phytoceramides were evaluated for their capacity to inhibit the proliferation of cancer cell lines. The preliminary results revealed that compound 21 exhibits promising anticancer activity against HeLa and HCT-116 cells as well as the excellent selectivity in cytotoxicity (malignant vs non-malignant cell lines).

Cascade Cope/Winstein Rearrangements: Synthesis of Azido-Cycloheptadienes from Dialkenylcyclopropanes Possessing a Vinyl Azide

cis-1,2-Dialkenylcyclopropanes incorporating a vinyl azide, generated by Knoevenagel condensations between the corresponding cyclopropanecarbaldehydes and α-azido ketones, undergo cascade Cope and Winstein [3,3]-sigmatropic rearrangements, under mild conditions. The sequence allows access to diversely substituted 1,4-cycloheptadienes armed with a secondary allylic azide with up to three stereocenters.

Selective hydroboration of equilibrating allylic azides

The iridium(I)-catalyzed hydroboration of equilibrating allylic azides is reported to provide only the anti-Markovnikov product of alk-1-ene isomers in good yields and with good functional group tolerance.

Seven-Step Synthesis of All-Nitrogenated Sugar Derivatives Using Sequential Overman Rearrangements

All-nitrogenated sugars (ANSs), in which all hydroxy groups in a carbohydrate are replaced with amino groups, are anticipated to be privileged structures with useful biological activities. However, ANS synthesis has been challenging due to the difficulty in the installation of multi-amino groups. We report herein the development of a concise synthetic route to peracetylated ANSs in seven steps from commercially available monosaccharides. The key to success is the use of the sequential Overman rearrangement, which enables formal simultaneous substitution of four or five hydroxy groups in monosaccharides with amino groups. A variety of ANSs are available through the same reaction sequence starting from different initial monosaccharides by chirality transfer of secondary alcohols. Transformations of the resulting peracetylated ANSs such as glycosylation and deacetylation are also demonstrated. Biological studies reveal that ANS-modified cholesterol show cytotoxicity against human cancer cell lines, whereas each ANS and cholesterol have no cytotoxicity.