Silylium ion equivalents have shown promise as Lewis acid catalysts for a range of important C-C bond-forming reactions. Here we describe chiral C-H acids that upon in situ silylation, generate silylium-carbanion pairs, which are extremely active Lewis acid catalysts for enantioselective Diels-Alder reactions of cinnamates with cyclopentadiene. Enantiomeric ratios of up to 97:3 and diastereomeric ratios of more than 20:1 are observed across a diverse set of substitution patterns with 1 mole percent (mol %) of C-H acid catalyst and 10 mol % of a silylating reagent. The results show promise for broad applications of such C-H acid-derived silylium ion equivalents in asymmetric Lewis acid catalysis.
α,β-Unsaturated esters are readily available but challenging substrates to activate in asymmetric catalysis. We now describe an efficient, general, and highly enantioselective Mukaiyama-Michael reaction of silyl ketene acetals with α,β-unsaturated methyl esters that is catalyzed by a silylium imidodiphosphorimidate (IDPi) Lewis acid.
Despite tremendous advances in enantioselective catalysis of the Diels-Alder reaction, the use of simple α,β-unsaturated esters, one of the most abundant and useful class of dienophiles, is still severely limited in scope due to their low reactivity. We report here a catalytic asymmetric Diels-Alder methodology for a large variety of α,βunsaturated methyl esters and different dienes based on extremely reactive silylium imidodiphosphorimidate (IDPi) Lewis acids. Mechanistic insights from accurate domainbased local pair natural orbital coupled-cluster (DLPNO-CCSD(T)) calculations rationalize the catalyst control and stereochemical outcome. The discovery of the Diels-Alder reaction by Kurt Alder and Otto Diels is regarded as one of the transforming events in organic chemistry. 1 The power and efficiency to rapidly build up complexity by forming up to four stereocenters at once was quickly realized and led to many important and elegant applications in the chemical synthesis of complex natural products, 2 agrochemicals, pharmaceuticals and fragrances.
Mesoporous silica nanoparticles (MSNs) attract increasing interest in the field of gene and drug delivery due to their versatile features as a multifunctional drug delivery platform.Here, we describe poly(amidoamine) (PAMAM) dendron-functionalized MSNs that fulfill key prerequisites for a controllable intracellular drug release. In addition to high loading capacity, they offer 1) low cytotoxicity, showing no impact on the metabolism of endothelial cells, 2) specific cancer cell targeting due to receptor-mediated cell uptake, 3) a redox-driven cleavage of disulfide bridges allowing for stimuli-responsive cargo release, and most importantly, 4) a specific internal trigger based on the high buffering capacity of PAMAM dendrons to provide endosomal escape.
α,β‐Ungesättigte Ester sind einfach zugängliche, aber schwierig zu aktivierende Substrate in der asymmetrischen Katalyse. Wir stellen hier eine effiziente, allgemeine und hochenantioselektive Mukaiyama‐Michael‐Reaktion von Silylketenacetalen mit α,β‐ungesättigten Methylestern vor, die durch silylierte Imidodiphosphorimidat(IDPi)‐Lewis‐Säuren katalysiert wird.
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