N-Heterocyclic-Carbene-Catalysed Diastereoselective Vinylogous Mukaiyama/Michael Reaction of 2-(Trimethylsilyloxy)furan and Enones

Silyldienolates in Organocatalytic Enantioselective Vinylogous Mukaiyama-Type Reactions: A Review

Mukaiyama aldol, Mannich, and Michael reactions are arguably amongst the most important C-C bond formation processes and enable access to highly relevant building blocks of various natural products. Their vinylogous extensions display equally high potential in the formation of important key intermediates featuring even higher functionalization possibilities through an additional conjugated C-C double bond. Hence, it is much desired to develop highly selective vinylogous methods in order to enable unconventional, more efficient asymmetric syntheses of biologically active compounds. In this regard, silyl-dienolates were discovered to display high regioselectivities due to their tendency toward γ-additions. The control of the enantio- and diastereoinduction of these processes have been for a long time dominated by transition metal catalysis, but it received serious competition by the application of organocatalytic approaches since the beginning of this century. In this review, the organocatalytic applications of silyl-dienolates in asymmetric vinylogous C-C bond formations are summarized, focusing on their scope, characteristics, and limitations.

An N-heterocyclic carbene-catalyzed switchable reaction of 9-(trimethylsilyl)fluorene and aldehydes: chemoselective synthesis of dibenzofulvenes and fluorenyl alcohols

An N-heterocyclic carbene-catalyzed synthesis of dibenzofulvenes and fluorenyl alcohols was developed. In the presence of 10 mol% NHC (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and 4 Å molecular sieves, 9-(trimethylsilyl)fluorene undergoes an olefination reaction with aldehydes to produce dibenzofulvenes in 43-99% yields. However, on reducing the NHC loading to 1 mol% and with the addition of water, 9-(trimethylsilyl)fluorene selectively undergoes nucleophilic addition with aldehydes to afford fluorenyl alcohols in 40-95% yields.

Organocatalytic aminocarbonylation of α,β-unsaturated ketones with N,N-dimethyl carbamoylsilane

Schwesinger's superbase can efficiently activate the Si–CONMe₂ bond and initiate the aminocarbonylation of α,β-unsaturated ketones and N,N-dimethyl carbamoylsilane.

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.

N-Heterocyclic carbene-catalyzed stereoselective construction of olefinic carbon–sulfur bonds via cross-coupling reaction of gem-difluoroalkenes and thiols

A novel organocatalytic olefinic carbon–sulfur bond forming reaction was developed.