Total synthesis of (+)-methynolide using a Ti-mediated aldol reaction of a lactyl-bearing oxazolidin-2-one, and a vinylogous Mukaiyama aldol reaction

New Developments of the Principle of Vinylogy as Applied to π-Extended Enolate-Type Donor Systems

The principle of vinylogy states that the electronic effects of a functional group in a molecule are possibly transmitted to a distal position through interposed conjugated multiple bonds. As an emblematic case, the nucleophilic character of a π-extended enolate-type chain system may be relayed from the legitimate α-site to the vinylogous γ, ε, ..., ω remote carbon sites along the chain, provided that suitable HOMO-raising strategies are adopted to transform the unsaturated pronucleophilic precursors into the reactive polyenolate species. On the other hand, when "unnatural" carbonyl ipso-sites are activated as nucleophiles (umpolung), vinylogation extends the nucleophilic character to "unnatural" β, δ, ... remote sites. Merging the principle of vinylogy with activation modalities and concepts such as iminium ion/enamine organocatalysis, NHC-organocatalysis, cooperative organo/metal catalysis, bifunctional organocatalysis, dicyanoalkylidene activation, and organocascade reactions represents an impressive step forward for all vinylogous transformations. This review article celebrates this evolutionary progress, by collecting, comparing, and critically describing the achievements made over the nine year period 2010-2018, in the generation of vinylogous enolate-type donor substrates and their use in chemical synthesis.

Very Recent Advances in Vinylogous Mukaiyama Aldol Reactions and Their Applications to Synthesis

It is a challenging objective in synthetic organic chemistry to create efficient access to biologically active compounds. In particular, one structural element which is frequently incorporated into the framework of complex natural products is a β-hydroxy ketone. In this context, the aldol reaction is the most important transformation to generate this structural element as it not only creates new C-C bonds but also establishes stereogenic centers. In recent years, a large variety of highly selective methodologies of aldol and aldol-type reactions have been put forward. In this regard, the vinylogous Mukaiyama aldol reaction (VMAR) became a pivotal transformation as it allows the synthesis of larger fragments while incorporating 1,5-relationships and generating two new stereocenters and one double bond simultaneously. This review summarizes and updates methodology-oriented and target-oriented research focused on the various aspects of the vinylogous Mukaiyama aldol (VMA) reaction. This manuscript comprehensively condenses the last four years of research, covering the period 2016-2019.

Enantiopure 4-oxazolin-2-ones and 4-methylene-2-oxazolidinones as chiral building blocks in a divergent asymmetric synthesis of heterocycles

Enantiopure 3-((R)- and 3-((S)-1-phenylethyl)-4-oxazoline-2-ones were evaluated as chiral building blocks for the divergent construction of heterocycles with stereogenic quaternary centers. The N-(R)- or N-(S)-1-phenylethyl group of these compounds proved to be an efficient chiral auxiliary for the asymmetric induction of the 4- and 5-positions of the 4-oxazolin-2-one ring through thermal and MW-promoted nucleophilic conjugated addition to Michael acceptors and alkyl halides. The resulting adducts were transformed via a cascade process into fused six-membered carbo- and heterocycles. The structure of the reaction products depended on the electrophiles and reaction conditions used. Alternative isomeric 4-methylene-2-oxazolidinones served as chiral precursors for a versatile and divergent approach to highly substituted cyclic carbamates. DFT quantum calculations showed that the formation of bicyclic pyranyl compounds was generated by a diastereoselective concerted hetero-Diels-Alder cycloaddition.

SuperQuat chiral auxiliaries: design, synthesis, and utility

The design, synthesis and outline of some of the most common synthetic applications of the SuperQuat (4-substituted 5,5-dimethyloxazolidine-2-one) family of chiral auxiliaries, developed to address the shortcomings of the Evans (4-substituted oxazolidin-2-one) family of chiral auxiliaries, are presented.

Remote Asymmetric Induction Reactions using a E, E-Vinylketene Silyl N, O-Acetal and the Wide Range Stereocontrol Strategy for the Synthesis of Polypropionates

The construction of libraries of acyclic polyketides remains a challenging topic, mostly due to the difficulties associated with finding the right balance between diversity and brevity for the synthetic routes leading to polyketides. Recently, relatively short methods have been developed and applied to the synthesis of natural products. However, these short routes often suffer from limited diversity with respect to the arrangement of functional groups and stereochemistry, as these usually require reactions that direct multiple functional groups simultaneously in one step. Therefore, methods that combine a small number of reaction steps with structural diversity remain an attractive research target for the construction of acyclic polyketide libraries. In 2004, we reported a remote asymmetric induction reaction using chiral vinylketene silyl N, O-acetal 1, which is commensurate to an anti-selective vinylogous Mukaiyama aldol reaction. Ever since, this reaction has been applied to the synthesis of numerous natural products, as this synthetic route is short and efficient on account of the simultaneous introduction of both asymmetric centers and the multiply functionalized carbon chain. Recently, we have developed a variety of this remote asymmetric induction reaction based on the E, E-vinylketene N, O-acetal 1, which includes syn-selective vinylogous Mukaiyama aldol reactions, as well as alkylation, acylation, and bromination reaction. These reactions provide polypropionates in a highly stereoselective manner. The proposed transition states of these reactions are discussed in this Account. Additionally, we have developed a new short synthesis of polypropionates by combining reactions for the remote asymmetric induction and the functionalization of double bonds (wide-range stereocontrol, WRS). The remote asymmetric induction reaction simultaneously constructs the stereogenic centers at the central part of the products and introduces the α,β-unsaturated imide, while the new strategy is based on the initial construction of the central part of the molecule and a subsequent functionalization of the surroundings (WRS). This strategy successfully furnished stereoisomers in a few steps, and the stereodivergent synthesis of 2,4,6-trimethyloctanoic acid derivatives was accomplished. This strategy should also be feasible to construct an acyclic polyketide library. Moreover, we applied this method to the concise synthesis of natural products. In this Account, the development of remote asymmetric induction reactions and the new WRS strategy are described. Applications of the WRS strategy as well as reactions for the stereodivergent synthesis of polypropionates and natural products are also described. The aforementioned acyclic polyketide library should be constructed in the future with the help of the WRS strategy and become a powerful tool in drug discovery.