Wittig Reactions of Trialkylphosphine-derived Ylides: New Directions and Applications in Organic Synthesis

Wittig and Wittig-Horner Reactions under Sonication Conditions

Carbonyl olefinations are among the most important organic syntheses that form C=C bonds, as they usually have high yields and in addition offer excellent stereoselectivity. Due to these advantages, carbonyl olefinations have important pharmaceutical and industrial applications. These reactions contain an additional step of an α-functionalized carbanion to an aldehyde or ketone to produce alkenes, but syntheses performed using metal carbene complexes are also known. The Wittig reaction is an example of carbonyl olefination, one of the best ways to synthesize alkenes. This involves the chemical reaction between an aldehyde or ketone with a so-called Wittig reagent, for instance phosphonium ylide. Triphenylphosphine-derived ylides and trialkylphosphine-derived ylides are the most common phosphorous compounds used as Wittig reagents. The Wittig reaction is commonly involved in the synthesis of novel anti-cancer and anti-viral compounds. In recent decades, the use of ultrasound on the Wittig reaction (and on different modified Wittig syntheses, such as the Wittig-Horner reaction or the aza-Wittig method) has been studied as a green synthesis. In addition to the advantage of green synthesis, the use of ultrasounds in general also improved the yield and reduced the reaction time. All of these chemical syntheses conducted under ultrasound will be described further in the present review.

A Dual CuH- and Pd-Catalyzed Stereoselective Synthesis of Highly Substituted 1,3-Dienes

Conjugated dienes are versatile building blocks and prevalent substructures in synthetic chemistry. Herein, we report a method for the stereoselective hydroalkenylation of alkynes, utilizing readily available enol triflates. We leveraged an in situ-generated and geometrically pure vinyl-Cu(I) species to form the Z,Z- or Z,E-1,3-dienes in excellent stereoselectivity and yield. This approach allowed for the synthesis of highly substituted Z-dienes, including pentasubstituted 1,3-dienes, which are difficult to prepare by existing approaches.

Methods of Synthesis of Remdesivir, Favipiravir, Hydroxychloroquine, and Chloroquine: Four Small Molecules Repurposed for Clinical Trials during the Covid-19 Pandemic

The novel coronavirus (COVID-19) disease has rapidly evolved into a sweeping pandemic despite public health measures. Screening and development of new vaccines and antivirals are expensive and time consuming. However, the repositioning of available drugs is an essential and universal strategy in the development of new drugs and therefore should receive priority attention as well as international government and agency support. Significant drugs such as chloroquine, hydroxychloroquine, favipiravir and remdesivir, are currently undergoing clinical studies to test their efficacy and safety. Some promising results have been achieved thus far in the treatment of COVID-19. In this article we summarize and discuss the most common synthetic strategies to apply in the preparation of these drug molecules. It is hoped that this compendium will provide an accessible useful guide and reference source for scientists, researchers and academia in their battle against COVD-19.

1 Introduction

2 Synthesis of Chloroquine (CQ) and Hydroxychloroquine (HCQ)

2.1 Synthesis of 4,7-Dichloroquinoline 1

2.2 Synthesis of 2-Amino-5-(diethylamino)pentane (Novoldiamine) 2

2.3 Synthesis of 5-(N-Ethyl-N-2-hydroxyethylamino)-2-pentylamine 4

2.4 Developed Methods for Synthesis of Chloroquine and Hydroxychloroquine

2.5 Synthesis of (R)-Chloroquine, (S)-Chloroquine, (R)-Hydroxychloroquine and (S)-Hydroxychloroquine

3 Synthesis of Favipiravir (Avigan)

4 Synthesis of Remdesivir

5 Conclusion

Silver catalyzed proto- and sila-Nakamura-type α-vinylation of silyl enol ethers with dichloroacetylene. Divergent formation of stereochemically pure tri- and tetrasubstituted olefins

The silver-catalyzed reaction of silyl enol ethers with dichloroacetylene (DCA) is described. When DCA was used as a solution in diethyl ether, we found that the silyl group was transferred to the vinyl group, resulting in stereochemically pure tetrasubstituted olefins. However, when DCA was used as a solution in the more polar acetonitrile, protonation was the major pathway, and trisubstituted olefins were the dominant products.

O-Heterocycles from Unsaturated Carbonyls and Dimethoxycarbene

The (4+1)-annulation of dimethoxycarbene with readily accessible α,β-unsaturated carbonyls gives cyclic orthoesters, which can then be converted in just a few steps to other O-heterocycles, including methoxyfurans, furanones, and furans.

Efficient phosphine-mediated formal C(sp3)–C(sp3) coupling reactions of alkyl halides in batch and flow

The Wittig-type chemical procedure is adapted to efficiently facilitate alkyl–alkyl coupling reactions in batch and flow.

Catalytic Wittig and aza-Wittig reactions

This review surveys the literature regarding the development of catalytic versions of the Wittig and aza-Wittig reactions. The first section summarizes how arsenic and tellurium-based catalytic Wittig-type reaction systems were developed first due to the relatively easy reduction of the oxides involved. This is followed by a presentation of the current state of the art regarding phosphine-catalyzed Wittig reactions. The second section covers the field of related catalytic aza-Wittig reactions that are catalyzed by both phosphine oxides and phosphines.

DualPhos: a versatile, chemoselective reagent for two-carbon aldehyde to latent (E)-alkenal homologation and application in the total synthesis of phomolide G

Advances on the use of the 2-pinacolacetal-tripropylphosphonium salt DualPhos as a general reagent for the two-carbon aldehyde to alkenal homologation and a chemoselective iron (III) chloride mediated deprotection are described. The strategy allows isolation of the latent alkenal intermediates or direct hydrolysis to (E)-alkenals. The robust chemical stability of the latent alkenals is demonstrated in a total synthesis of the macrolactone phomolide G.