Gold(I)-Catalyzed Addition of Diphenyl Phosphate to Alkynes: Isomerization of Kinetic Enol Phosphates to the Thermodynamically Favored Isomers

Synthesis of Five-Membered Cyclic Phosphinic Acids via the [4C+1P] Cyclization of 1,3-Dienes with a Combination of PBr3 and P(OMe)3 as the P(III) Source

An efficient method for the synthesis of 1-hydroxy-2,5-dihydrophosphole 1-oxides, a type of five-membered P-containing heterocyclic compound, is presented. The reaction was carried out through a [4C+1P] cyclization of 1,3-dienes with a combination of PBr3 and P(OMe)3 as the P(III) source. To compare with the reported methods, the protocol reported herein not only is much milder and more rapid but also displays a broad substrate scope and affords the products in high yields (50-94%). In addition, the reaction could be reliably scaled up at the gram-scale level and was demonstrated to be a versatile platform for flexible derivatization. Consequently, this method provides a general and reliable way for the synthesis of five-membered phosphole derivatives.

The core of the matter - arene substitution determines the coordination and catalytic behaviour of tris(1-phosphanyl-1'-ferrocenylene)arene gold(I) complexes

Changing the aromatic core of C3-symmetric tris(ferrocenyl)arene-based tris-phosphanes has profound effects on their coordination behaviour towards gold(i). Depending on the arene (s-triazine, benzene, or trifluorobenzene), four different coordination modes can be distinguished and their preference has been rationalised using computational methods. The corresponding 1 : 1 ligand-to-metal complexes, studied by variable-temperature NMR spectroscopy, revealed fluctional behaviour in solution. Given the presence of up to three or six ferrocenylene spacers per complex, their electrochemistry was investigated. The redox-responsive nature of the complexes can be advantageously exploited in the catalytic ring-closing isomerisation of N-(2-propyn-1-yl)benzamide, where the benzene-based 2 : 3 ligand-to-metal complex has been shown to display multiple activity states depending on the degree of (reversible) oxidation in a preliminary trial.

Synthesis of 2-Aminophosphates via SN2-Type Ring Openings of Aziridines with Organophosphoric Acids

The synthesis of 2-aminophosphates is achieved by a S_N2-type ring opening reaction of various N-protected or free aziridines with phosphoric acids in a regiospecific and/or enantiospecific way. A one-pot, two-step procedure is also developed enabling direct access to 2-aminophosphates from olefins without isolation of the aziridine intermediates.

Redox-responsive phosphonite gold complexes in hydroamination catalysis

Very high activities were observed in the redox-induced hydroamination of alkynes by employing a redox-active gold(i) complex featuring an electron-deficient, terphenyl-substituted phosphonite-based ligand. The hydroamination proceeds roughly two-fold faster with the in situ oxidized catalysts than with their reduced form.

The synthesis of pyrroles and oxazoles based on gold α-imino carbene complexes

Cationic gold complexes of α-oximimino carbenes have been identified to react with weak nucleophiles including enol ethers and nitriles. These findings allowed us to develop the highly efficient synthesis of pyrroles and oxazoles.

Regioselective addition of phosphites to acyl cyclopropanes and following rearrangements: a facile access to enol phosphates

This work describes a novel method of preparing functionalized enol phosphates with acyl cyclopropanes through a regioselective cascade reaction.

Selective Alkenylation and Hydroalkenylation of Enol Phosphates through Direct C-H Functionalization

An efficient and selective Rh-catalyzed direct CH functionalization reaction of enol phosphates was developed. The method is applicable to a variety of coupling partners, including activated alkenes, alkynes, and allenes, and leads to the formation of various valuable alkenylated and hydroalkenylated enol phosphates through the action of the phosphate directing group. The versatility and utility of the coupling products were demonstrated through further transformations into synthetically useful building blocks.

Efficient methods for enol phosphate synthesis using carbon-centred magnesium bases

Efficient conversion of ketones into enol phosphates under mild and accessible conditions has been realised using the developed methods with di-tert-butylmagnesium and bismesitylmagnesium. Optimisation of the quench protocol resulted in high yields of enol phosphates from a range of cyclohexanones and aryl methyl ketones.

Gold-catalyzed intermolecular C-S bond formation: efficient synthesis of α-substituted vinyl sulfones

A general method for the synthesis of α-substituted vinyl sulfones makes use of a combination of a triazole gold complex and gallium triflate. This efficient CS bond formation between simple terminal alkynes and sulfinic acids provides access to various α-substituted vinyl sulfones.

Ambient gold-catalyzed O-vinylation of cyclic 1,3-diketone: A vinyl ether synthesis

Gold-catalyzed O-vinylation of cyclic 1,3-diketones has been achieved for the first time, which provides direct access to various vinyl ethers. A catalytic amount of copper triflate was identified as the significant additive in promoting this transformation. Both aromatic and aliphatic alkynes are suitable substrates with good to excellent yields.

Rhodium-catalyzed oxidative C-H activation/cyclization for the synthesis of phosphaisocoumarins and phosphorous 2-pyrones

Rhodium-catalyzed cyclization of phosphinic acids and phosphonic monoesters with alkynes has been developed. The oxidative annulation proceeds with complete conversion of phosphinic acid derivatives and allowed the atom-economic preparation of useful phosphaisocoumarins with high yield and selectivity. The reaction is tolerant of extensive substitution on the phosphinic acid, phosphonic monoester and alkyne, including halides, ketone, and hydroxyl groups as substituents. Furthermore, we found that alkenylphosphonic monoesters proceed to give a wide range of phosphorus 2-pyrones through oxidative annulation with alkynes. Mechanistic studies revealed that C-H bond metalation was the rate-limiting step.

Rhodium-catalyzed oxidative cyclization of arylphosphonic acid monoethyl esters with alkenes: efficient synthesis of benzoxaphosphole 1-oxides

Rhodium-catalyzed tandem oxidative alkenylation and an intramolecular oxy-Michael reaction were developed using arylphosphonic acid monoethyl esters and alkenes under aerobic conditions, which produced benzoxaphosphole 1-oxides in good to excellent yields.

Gold-catalyzed oxycyclization of allenic carbamates: expeditious synthesis of 1,3-oxazin-2-ones

A combined experimental and computational study on regioselective gold-catalyzed synthetic routes to 1,3-oxazinan-2-ones (kinetically controlled products) and 1,3-oxazin-2-one derivatives (thermodynamically favored) from easily accessible allenic carbamates has been carried out.

Transition metal-catalysed cross-coupling reactions of P-activated enols

Transition metal catalysed cross-coupling reactions are ubiquitous in organic chemistry providing an impressive technique for C-C bond formation. Whilst many electrophilic partners have been described for these reactions, aryl and vinyl phosphates, phosphonates and phosphonites can offer advantages in terms of preparation, stability and reactivity profile. This critical review summarises the advances made to date utilising P-activated enols in metal-catalysed cross-coupling reactions (97 references).

Syntheses of α-pyrones using gold-catalyzed coupling reactions

Sequential alkyne activation of terminal alkynes and propiolic acids by gold(I) catalysts yields compounds having α-pyrone skeletons. Novel cascade reactions involving propiolic acids are reported that give rise to α-pyrones with different substitution patterns.