Most of the methods for the creation of all-carbon quaternary stereogenic centers in acyclic systems were developed in the last decade showing the contemporary interest of this field of research. Initial strategies, where chiral entities were linked to carbon skeleton, to enantioselective catalysis and finally to strategies where several carbon-carbon bonds were created in a single-pot operation, reflect the constant strive and creativity in the design and execution of synthetic sequences. This feature article summarizes these sequences and is divided into sections on substitution and additions reactions, alkylation, aldol, Mannich and rearrangements reactions. It is safe to predict that this field of chemistry will continue to grow exponentially in the coming decades and the ready availability of a wide range of these chiral entities will provide an excellent opportunity to further enrich mainstream synthetic methodologies.

In the past few decades, it has become clear that asymmetric catalysis is one of the most powerful methods for the construction of carbon-carbon as well as carbon-heteroatom bonds in a stereoselective manner. However, when structural complexity increases (i.e., all-carbon quaternary stereogenic center), the difficulty in reaching the desired adducts through asymmetric catalytic reactions leads to a single carbon-carbon bond-forming event per chemical step between two components. Issues of efficiency and convergence should therefore be addressed to avoid extraneous chemical steps. In this Perspective, we present approaches that tackle the stimulating problem of efficiency while answering interesting synthetic challenges. Ideally, if one could create all-carbon quaternary stereogenic centers via the creation of several new carbon-carbon bonds in an acyclic system and in a single-pot operation from simple precursors, it would certainly open new horizons toward solving the synthetic problems. Even more important for any further design, the presence of polyreactive intermediates in synthesis (bismetalated, carbenoid, and oxenoids species) becomes now an indispensable tool, as it creates consecutively the same number of carbon-carbon bonds as in a multi-step process, but in a single-pot operation.

Among the challenges facing asymmetric synthesis the selective construction of quaternary stereogenic centres, particularly those bearing all-carbon substituents, stands out. The aldol reaction has the potential to create such stereocentres, but, despite the many advances in this field, a highly selective and efficient procedure has remained elusive. Here we show that, by choosing an alternative retrosynthetic approach, such products can be prepared in a highly selective fashion. Through the consecutive addition of several organometallic derivatives, an allylzinc reagent is prepared and, on addition to an aldehyde, an aldol-type product is created. The one-pot operation involves the construction of three new carbon-carbon bonds and the formation of an all-carbon quaternary stereocentre. The products of the reaction are amenable to downstream modification, and the procedure should find applications in the fields of natural product synthesis and drug discovery.

UV-vis spectrophotometry is utilized to measure the relative efficiency of lithium acetate, tetrabutylammonium trifluoroacetate, and triethylamine as catalysts for the conversion of 4-methoxycinnamic acid to 4-methoxy-beta-bromostyrene. In acetonitrile-water as solvent, the efficiency order is lithium acetate > triethylamine > tetrabutylammonium trifluoroacetate. For triethylamine as catalyst, solvent-dependent order is acetonitrile-water > dichloromethane > acetonitrile. Using triethylamine as catalyst (5-20 mol %), cinnamic acids, and propiolic acids are converted to corresponding beta-bromostyrenes and 1-halo-1-alkynes in 60-98% isolated yields within 1-5 min.

The selenodecarboxylation of phenylpropiolic and cinnamic acid derivatives with diorgano diselenide is promoted by iodosobenzene diacetate (PhI(OAc)2, IBDA) in acetonitrile at 30−60 °C, leading to the formation of alkynyl selenides and vinyl selenides in moderate to excellent yields. Similar reactivity is also shown by iodosylbenzene (PhIO, IB). The reaction is also triggered in the solid state. An electrophilic mechanism is proposed for the transformation.

[reaction: see text] The nitrodecarboxylation of aromatic alpha,beta-unsaturated carboxylic acids and ring-activated benzoic acids can be achieved using nitric acid (3 equiv) and catalytic AIBN (2 mol %) in MeCN. From the effect of various additives, the nitrodecarboxylation is postulated to involve the generation of an acyloxy radical RCO(2)(*) by a NO(3)(*) radical followed by attack of a NO(2)(*) radical.

A Nitro-Hunsdiecker Reaction: From Unsaturated Carboxylic Acids to Nitrostyrenes and Nitroarenes. -Present nitrodecarboxylation is proposed to proceed via generation of an radical by followed by attack of an radical. -(DAS, J. P.; SINHA, P.; ROY*, S.;

A Cu I -catalyzed hydrocupration and borylation protocol for the regio-and stereoselective borylation of ynamides utilizing pinacolatoborane (HBpin) as the borylating agent has been developed. The reaction features mild conditions, good substrate scope and functional group tolerance-representing a highly efficient and practical method for the synthesis of regio-and stereoselective tri-substituted alkenylboronates from readily available ynamides. The regioselectivity is controlled by altering substituents on the ynamides (alkyl vs aryl) and utilizing a catalytic species [LCuH] generated in situ from HBpin and [LCuX]. Suzuki coupling and other transformations highlight the synthetic utility of the method.