Photocatalytic Synthesis of β-Keto Primary Chlorides by Selective Chlorocarbonylation of Olefins

Functionalized primary alkyl chlorides are precursors to a plethora of scaffolds but their access from chemical feedstocks remains challenging. Herein, we report a concise dual Ni/photoredox catalytic protocol for regioselective chlorocarbonylation of unactivated alkenes that enables rapid access to β-keto primary chlorides. The catalytic process features an extensive substrate scope, scalability and functional group tolerance. The Ni/photocatalytic Cl⋅ generation and subsequent cross-coupling is implicated for the process based on the control experiments and DFT study. The synthetic utility of the protocol has been further corroborated through functionalization of complex substrates and modifications of the product.

The Synthetic Approaches to 1,2-Chlorohydrins

This short review highlights the hitherto realised synthetic approaches towards organic 1,2-chlorohydrins by functionalisation of alkenes (i.e., 1,2-chlorohydroxylation), which is the most prominent access route to this class of compounds. Also, some other synthetic approaches involving the reduction of α-chloroketones, the epoxide opening ring by chloride anions and the utilisation of Grignard reagents for the synthesis of these compounds and chlorination of allylic alcohols are highlighted. Finally, enzymatic reactions for the formation of chlorohydrins are briefly summarised followed by a short view on natural products containing this moiety.

1 Introduction

2 Applications for the Synthesis of 1,2-Chlorohydrins

2.1 Chlorohydroxylation of Alkenes

2.2 Reduction of Chloroketones

2.3 Metalorganic Reagents

2.4 Epoxide Ring Opening

2.5 Chlorination of Allylic Alcohols

2.6 Biochemical Methods

2.7 Selected Applications in Natural Product Total Synthesis

3 Conclusion

Halohydroxylation of alkenyl MIDA boronates: switchable stereoselectivity induced by B(MIDA) substituent

A switchable stereoselectivity in the halohydroxylation of alkenyl MIDA boronates was found. C–B(MIDA) bond hyperconjugation plays the key role.

Neighboring Effect of Intramolecular Chlorine Atoms on Epoxide Opening Reaction by Chloride Anions

We investigated the diastereoselectivity of ring openings for chloro vinyl epoxides with various chlorination reagents. In the chlorinolysis reactions using vinyl epoxides having an allyl alcohol, inversion:retention ratios varied depending on the chloride sources. In limited cases, the increase in retention ratio was consistent with the intervention of chloronium ions. In contrast, all vinyl epoxides bearing an α,β-unsaturated ester gave only the inversion products. These results suggest the electron-withdrawing property suppressed the chloronium ions.

Highly functionalised (γ-azido/γ-fluoro-β-iodo/)vinyl derivatives from phosphorus based allenes or allenoates: I⋯O halogen bonding interactions

γ-Azido/γ-fluoro-β-iodo-vinyl phosphine oxides/phosphonates/esters/sulphone and a γ-diodoallene were synthesised from phosphorus-based allenes or allenoates or a sulphur based allene; in many cases, I⋯O halogen bonding is observed in the solid state.

Synthesis of Vicinal Dichlorides via Activation of Aliphatic Terminal Epoxides with Triphosgene and Pyridine

Herein we report a novel synthetic reaction to convert unactivated terminal aliphatic epoxide to alkyl vicinal dichloride based on triphosgene-pyridine activation. Our methodology is operationally simple and readily tolerated by a broad of scope of substrates as well as protecting groups. Furthermore, these mild conditions generally yield clean reaction mixtures that are free of byproducts upon aqueous workup.

Stereochemistry and biological activity of chlorinated lipids: a study of danicalipin A and selected diastereomers

The syntheses of (+)-16-epi- and (+)-11,15-di-epi-danicalipin A (2 and 3) are reported. The conformations of the parent diols 5 and 6 as well as the corresponding disulfates 2 and 3 were determined on the basis of J-based configuration analysis and supported by calculations. The impact of configuration on membrane permeability in Gram-negative bacteria and mammalian cell lines was assessed as well as cytotoxicity. Although diastereomer 2 showed similar behavior to natural (+)-danicalipin A (1), strikingly, the more flexible C11,C15-epimer 3 had no effect on permeability and proved equally or more toxic towards multiple cell lines.

Difunctionalization of Alkenes Using 1-Chloro-1,2-benziodoxol-3-(1H)-one

Difunctionalization of alkenes with 1-chloro-1,2-benziodoxol-3-(1H)-one (1) was investigated. Various additional nucleophiles were tested, and oxychlorination, dichlorination, azidochlorination, chlorothiocyanation, and iodoesterfication were demonstrated. The oxychlorination product was obtained efficiently when the reaction was operated in water. Dichlorination occurred in the presence of a Lewis basic promoter, such as 4-phenylpyridine N-oxide, as an additive. The reaction with in situ-generated azido anion afforded azidochlorinated compounds with a chlorine atom at the terminal position, while the reaction with trimethylsilyl isothiocyanate produced chlorothiocyanation adducts with a chlorine atom at the benzylic position. On the other hand, when 1 was treated with tetra-n-butylammonium iodide prior to the addition of alkenes, only iodoesterification occurred selectively. These mild reactions enable convenient site-selective difunctionalizations of substrates having two alkene moieties. NMR experiments suggested that the electrophilic reactive species in each reaction varied depending on the nature of the added nucleophile.

A simple and highly diasteroselective approach for the vicinal dichlorination of functional olefins

An efficient strategy for triphenylphosphine oxide-catalyzed vicinal dichlorination of functional olefins was developed using sulfuryl chloride as the source of chloride.

Catalytic, Stereoselective Dihalogenation of Alkenes: Challenges and Opportunities

Although recent years have witnessed significant advances in the development of catalytic, enantioselective halofunctionalizations of alkenes, the related dihalogenation of olefins to afford enantioenriched vicinal dihalide products remains comparatively underdeveloped. However, the growing number of complex natural products bearing halogen atoms at stereogenic centers has underscored this critical gap in the synthetic chemist's arsenal. This Review highlights the selectivity challenges inherent in the design of enantioselective dihalogenation processes, and formulates a mechanism-based classification of alkene dihalogenations, including those that may circumvent the "classical" haliranium (or alkene-dihalogen π-complex) intermediates. A variety of metal and main group halide reagents that have been used for the dichlorination or dibromination of alkenes are discussed, and the proposed mechanisms of these transformations are critically evaluated.

Catalytic, stereospecific syn-dichlorination of alkenes

As some of the oldest organic chemical reactions known, the ionic additions of elemental halogens such as bromine and chlorine to alkenes are prototypical examples of stereospecific reactions, typically delivering vicinal dihalides resulting from anti-addition. Although the invention of enantioselective variants is an ongoing challenge, the ability to overturn the intrinsic anti-diastereospecificity of these transformations is also a largely unsolved problem. Here, we describe the first catalytic, syn-stereospecific dichlorination of alkenes, employing a group transfer catalyst based on a redox-active main group element (selenium). With diphenyl diselenide (PhSeSePh) (5 mol%) as the pre-catalyst, benzyltriethylammonium chloride (BnEt3NCl) as the chloride source and an N-fluoropyridinium salt as the oxidant, a wide variety of functionalized cyclic and acyclic 1,2-disubstituted alkenes, including simple allylic alcohols, deliver syn-dichlorides with exquisite stereocontrol. This methodology is expected to find applications in streamlining the synthesis of polychlorinated natural products such as the chlorosulfolipids.

Convenient in situ generation of various dichlorinating agents from oxone and chloride: diastereoselective dichlorination of allylic and homoallylic alcohol derivatives

A safe and convenient protocol was developed for in situ generation of various dichlorinating agents (cf. Cl2, NCl3, Et4NCl3, ArICl2) from oxone and chloride. The synthetic utility of this protocol was demonstrated by diastereoselective dichlorination of a series of allylic and homoallylic alcohol derivatives with excellent yields and diastereoselectivity.