An efficient synthesis of functionalized tertiary α‐silyl alcohols by an enantio‐ and diastereoselective copper‐catalyzed three‐component coupling of 1,3‐dienes, bis(pinacolato)diboron, and ...acylsilanes is reported. The reaction proceeds well with different 1,3‐dienes and a broad range of aryl‐ as well as alkenyl‐ but also alkyl‐substituted acylsilanes. The target compounds are formed with high regio‐, diastereo‐, and enantioselectivity (up to 99 % ee and d.r. >20:1) and are highly versatile synthetic building blocks.
All at once: A copper‐catalyzed three‐component coupling of 1,3‐dienes, bis(pinacolato)diboron, and acylsilanes affords densely functionalized tertiary α‐silyl alcohols regioselectively in high yields as well as with excellent enantioselectivity (up to 99 % ee) and diastereoselectivity (d.r. >20:1). Subsequent transformations illustrate the versatility of these chiral building blocks.
Si-B reagents, namely silylboronic esters and silylboranes, have become increasingly attractive as versatile reagents to introduce silicon and boron atoms into organic frameworks. Diverse ...transformations through transition-metal-catalysed or transition-metal-free Si-B bond activation have become available. This Review summarises the recent developments in the now broad field of Si-B chemistry and covers the literature from the last seven years as an update of our review on the same topic published in early 2013 (M. Oestreich, E. Hartmann and M. Mewald,
Chem. Rev
., 2013,
113
, 402-441). It mainly focuses on new applications of Si-B reagents but new methods of their preparation and, where relevant, reaction mechanisms are also discussed.
Covering the past seven years, this review comprehensively summarises the latest progress in the preparation and application of Si-B reagents, including the discussion of relevant reaction mechanisms.
The unique structure and reactivity of the aziridine ring has attracted the interest of organic chemists for many years. Of these, the cycloaddition of alkynes with aziridines via C–C bond and C–N ...bond cleavage is an atom-efficient and convergent approach to the preparation of valuable unsaturated N-heterocycles. In this Perspective, progress in this field is outlined on the basis of the key intermediate involved in the reaction. In addition to the cycloadditions of azomethine ylides generated by carbon–carbon bond cleavage and aziridinium ions and zwitterionic 1,3-dipoles generated by carbon–nitrogen bond cleavage, the new type of cycloadditions of aziridines and alkynes involving metalla-azetidine intermediates has been highlighted in this short review. The use of methyleneaziridine in the cycloaddition reactions with alkynes is also discussed. Contrary to noncatalytic cycloadditions of aziridines with alkynes via azomethine ylides or aziridinium ions, the catalytic cycloadditions for synthesis of unsaturated N-heterocycles from aziridines and alkynes have more opportunity to improve the efficiency and selectivity of the reaction and to expand their synthetic utility.
A new synthetic application of vinyl aziridines as N‐containing three‐atom components in a rhodium‐catalyzed 4+3 cycloaddition reaction is described. The reaction proceeds well with various silyl ...dienol ethers and vinyl aziridines, and enables the efficient synthesis of highly functionalized azepines in an enantioselective manner with net inversion of absolute configuration. The salient features of the transformation include the use of readily available substrates, high selectivity, and mild reaction conditions, as well as the versatile functionalization of the products.
Strike a happy medium: The title reaction, in which the vinyl aziridine acts as an aza‐three‐atom component, provided highly functionalized azepines in an enantioselective manner with net inversion of configuration (see scheme; Si is a silyl protecting group). This strategy features the use of readily available substrates, high selectivity, mild reaction conditions, ease of scale‐up, and versatile functionalization of the products.
A copper-catalyzed three-component coupling of 1,3-dienes, bis(pinacolato)diboron, and ketones allows for the chemo-, regio-, diastereo- and enantioselective assembly of densely functionalized ...tertiary homoallylic alcohols. The relative configuration of the vicinal stereocenters is controlled by the chiral ligand employed. Subsequent transformations illustrate the versatility of these valuable chiral building blocks.
A ligand-controlled diastereodivergent copper-catalyzed borylative coupling between 1,3-dienes and ketones enables the enantioselective synthesis of densely functionalized tertiary homoallylic alcohols.
The first rhodium‐catalyzed intramolecular hetero‐5+2 cycloaddition reaction of vinyl aziridines and alkenes was realized, wherein both internal and terminal alkenes were applicable. With this ...method, a variety of unique substituted chiral fused bicyclic azepines, bearing multiple contiguous stereogenic centers, were facilely accessed in a straightforward, high‐yielding, and highly stereoselective manner under mild reaction conditions. Notably, the E/Z geometry of the CC bonds in the vinyl aziridine‐alkene substrates impact the cis/trans stereochemistry of the cycloadducts and up to six stereoisomers could be delivered.
E/Z access: The title reaction was realized and a range of chiral fused bicyclic azepines bearing multiple contiguous stereogenic centers can be obtained in a high‐yielding and stereoselective manner. The E/Z geometry of the CC bonds in the substrates affect the stereochemistry of the cycloadducts and up to six stereoisomers can be obtained.
Bicyclo2.1.1hexanes (BCHs) are becoming ever more important in drug design and development as bridged scaffolds that provide underexplored chemical space, but are difficult to access. Here a ...silver‐catalyzed dearomative 2π+2σ cycloaddition strategy for the synthesis of indoline fused BCHs from N‐unprotected indoles and bicyclobutane precursors is described. The strain‐release dearomative cycloaddition operates under mild conditions, tolerating a wide range of functional groups. It is capable of forming BCHs with up to four contiguous quaternary carbon centers, achieving yields of up to 99 %. In addition, a scale‐up experiment and the synthetic transformations of the cycloadducts further highlighted the synthetic utility.
A silver Lewis acid catalyzes dearomative 2π+2σ cycloadditions of N‐unprotected indoles and bicyclobutanes to afford indoline fused bicyclo2.1.1hexanes (BCHs) bearing up to four contiguous quaternary carbon centers in high yields and with an opposite regioselectivity compared to the classical pathway.
The first rhodium‐catalyzed intermolecular 3+2 cycloaddition reaction of vinyl aziridines and allenes for the synthesis of enantioenriched functionalized pyrrolidines was realized. 3+2 cycloaddition ...with the proximal C=C bond of N‐allenamides gave 3‐methylene‐pyrrolidines in high regio‐ and diastereoselectivity, whereas, 2‐methylene‐pyrrolidines were obtained as the major products by the cycloadditions of vinyl aziridines with the distal C=C bond of allenes. Use of readily available starting materials, a broad substrate scope, high selectivity, mild reaction conditions, as well as versatile functionalization of the cycloadducts make this approach very practical and attractive.
Adding together rapidly: A regiodivergent synthesis of enantioenriched functionalized pyrrolidines, such as 2‐methylene‐ and 3‐methylene‐pyrrolidines, has been developed through a regioselective 3+2 cycloaddition of vinyl aziridines with allenes and N‐alleneamines, respectively. The reaction demonstrates general substrate scope, mild conditions, atom‐economy, and proceeds with complete chirality transfer.
By taking advantage of vinyl aziridines as a heteroatom-containing five-atom component in rhodium-catalyzed intramolecular formal hetero-5 + 2 cycloaddition reactions with alkynes, a highly efficient ...method for the synthesis of fused azepine derivatives at 30 °C was developed. The reaction has broad substrate scope and tolerates a wide range of functional groups. The chirality of vinyl aziridine-alkyne substrates can be completely transferred to the cycloadducts, representing an atom-economic and enantiospecific protocol for the construction of fused 2,5-dihydroazepines for the first time.
An asymmetric addition of diarylphosphines to β-substituted enones under mild conditions using a chiral pincer−palladium catalyst has been developed for the synthesis of chiral phosphines with ...excellent stereoselectivity (up to 99% ee).
PDF
