Have it both ways: Enantiomerically enriched E vinyl glycines may be accessed from aldehydes in a concise sequence that combines an organocatalytic α sulfenylation, stereoselective olefination, a sulfimidation, and a [2,3] sigmatropic rearrangement (see scheme, Boc=tert‐butoxycarbonyl, nHex=n‐hexyl). Either enantiomeric series can be accessed by control of the alkene geometry in the olefination step.

Reaction of branched allylic sulfides with the N-Boc-oxaziridine 1 results in [2,3]-sigmatropic rearrangement of the intermediate allylic N-Boc-sulfimides with a high level of chirality transfer. The first example of formation of a quaternary stereocenter using this transformation is reported.

Freie Wahl: Enantiomerenangereicherte E‐Vinylglycine lassen sich aus Aldehyden in einer einfachen Sequenz herstellen, die eine organokatalytische α‐Sulfenylierung mit einer stereoselektiven Olefinierung, einer Sulfimidierung und einer [2,3]‐sigmatropen Umlagerung kombiniert (siehe Schema, Boc=tert‐Butoxycarbonyl, nHex=n‐Hexyl). Über das Einstellen der Doppelbindungskonfiguration im Olefinierungsschritt sind beide Enantiomere zugänglich.

A D e s y m m e t r i s e d C a r b o h y d r a t e R e c e p t o rAbstract: We report a new addition to the family of biphenyl-based carbohydrate receptors, derived by replacing one out of four isophthalamide (diamide) linkages with the corresponding diester. The alteration results in lower binding constants, perhaps reflecting the entropic penalty for lowering receptor symmetry. However, the synthesis allows access to many related host molecules, with potential for restoring and raising affinities and tuning selectivities.Carbohydrate recognition continues to attract the interest of supramolecular chemists. 1,2 On the one hand, saccharides are challenging substrates because of their complexity and the subtle differences between their structures. On the other they hold great importance for biology, not only as fuels and structural materials but also as labels for cells and proteins. 3 We have developed a family of oligophenyl-based receptors which have successfully targeted 'all-equatorial' carbohydrates (glucose, b-glucosides, cellobiose, etc.). 4 The design strategy is illustrated in Figure 1 (a) for the monosaccharide receptors 1. 4a-c Two biphenyl units serve as roof and floor of a tricyclic cage, providing apolar surfaces which complement the axial CH groups of a b-glucosyl substrate 2. The aromatic surfaces can contribute to binding through CH-p interactions in nonpolar solvents, and through hydrophobic interactions in water. The biphenyls are separated by isophthalamide pillars that can hydrogen bond to the equatorially directed polar groups of the substrate. Solubility is controlled by externally directed groups X (lipophilic for organic-soluble 1a and 1b, 4a,b charged for water-soluble 1c 4c ). The receptors show useful binding properties in a full range of solvents, 5 with good-to-excellent selectivities for their intended targets.Given the asymmetry of the carbohydrate substrates, it seems unlikely that the highly symmetrical structure 1 is optimal for binding; a receptor which is perfectly complementary for 2 should reflect the asymmetry of 2. Moreover, less-symmetrical cages might show altered and complementary selectivities. We have previously described the preparation of receptors in which the ends of the cage are differentiated, through the presence or absence of a pyridine nitrogen. 6 In the present work we aimed to lower symmetry still further, by changing one corner of the cage. We were also interested to test the effect of removing H-bonding functionality from a pillar. Molecular modelling 4a suggested that, in the ground state conformation of complex 1 + 2 (R = OH), one of the isophthalamide units of 1 makes no hydrogen bonds with the carbohydrate. If so, the amides in this pillar might not be needed for strong binding. We were therefore drawn to receptor 3 (Figure 1, b), an analogue of 1b in which one isophthalamide is replaced by a diester (isophthalate) unit. Esters cannot act as H-bond donors, and are also relatively poor H-bond acceptors. We now report the successful synthesis of 3, an...