1,721,078 research outputs found
Shaping Chirality via Stereoselective, Organocatalytic [4+2] Cycloadditions involving Heterocyclic ortho‐Quinodimethanes
No full textPolycyclic compounds bearing a complex heterocyclic core such as an aromatic heterocycle "fused" with one or more functionalized rings, are widespread leading molecules in the domain of synthetic organic chemistry and pharmaceuticals. Although many synthetic methodologies have been devised to access achiral, fused heteroaromatic scaffolds, or related chiral variants adorned with out-of-cycle stereogenic elements, equally efficient strategies to afford chiral heterocycles featuring in-cycle stereocenters, exist to a lesser extent and presently represent a growing field of investigation. The mild, organocatalytic generation of elusive ortho-quinodimethane intermediates (oQDMs), derived from suitable heteroaromatic carbonyl- or carbonyl-like pronucleophiles has recently proved successful in the synthesis of such peculiar chiral architectures via stereoselective [4+2] cycloadditions. This review provides an overview of the most important advances attained in this field over the last decade
Method- and Target-Oriented Organic Synthesis: Invaluable Opportunities in Contemporary Drug Discovery
No full textUna nuova Metodologia per la Sintesi di carbachetosi ed Analoghi: Acidi Glutammici Conformazionalmente Costretti
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Tuning the Reactivity of Silyloxy Pyrroles Towards Catalytic, Enantioselective, Vinylogous Mukaiyama Aldol and Mannich Processes
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3-Alkylidene-2-oxindoles in Vinylogous Mukaiyama Mannich Reactions: Synthesis of Multifaceted Aminated Scaffolds
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Direct, Organocatalytic, Enantioseletcive Michael Reactions: Turning Common Michael Acceptors Into Vinylogous Carbon Nucleophiles
No full textalpha,beta-Unsaturated carbonyl or carbonyl-like moieties are usually envisaged as privileged electrophilic functionalities to be exploited, among others, in Michael addition reactions as well as synchronous or stepwise cycloadditions, opening the way to a wide range of highly valuable beta-functionalized scaffolds. However, behind this common reactivity pattern, an “umpolung” option can be unveiled when an enolizable alkyl group is present at the beta-position of the ylidene. In fact, using a suitable activating catalyst and capitalizing on the vinylogous pro-nucleophilic character of the alkyl group, an addition reaction of these substrates to proper electrophilic acceptors can be fostered to yield olefinic products functionalized at the most distant point of the molecule (C-gamma). We were able to proof this concept on several multidentate scaffolds, namely 3-alkylidene oxindoles,[1] alpha-alkylidene pyrazolinones[2] and dicyano-olefins,[3] by developing direct, organocatalytic, asymmetric, vinylogous Michael addition reactions using nitroolefins or unsaturated aldehydes as electrophilic counterparts. Based on stereocontrolled, covalent or non-covalent dual activation modes, the Cinchona- or prolinol-based organocatalysts performed well, promoting the reactions in high yields and with remarkable control of the regio-, diastereo- and enantioselectivity.
References
1. (a) Curti, C.; Rassu, G.; Zambrano, V.; Pinna, L.; Pelosi, G.; Sartori, A.; Battistini, L.; Zanardi, F.; Casiraghi, G. Angew. Chem. Int. Ed. 2012, 51, 6200. (b) Rassu, G.; Zambrano, V.; Pinna, L.; Curti, C.; Battistini, L.; Sartori, A.; Pelosi, G.; Zanardi, F.; Casiraghi, G. Adv. Synth. Catal. 2013, 355, 1881.
2. Rassu, G.; Zambrano, V.; Pinna, L.; Curti, C.; Battistini, L.; Sartori, A.; Zanardi, F.; Casiraghi, G. Adv. Synth. Catal. 2014, accepted.
3. Dell’Amico, L.; Curti, C.; Zanardi, F. et al. manuscript in preparation
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