Synlett

N-(Difluoropropenyl)amides/amines are an important class of fluorinated compounds. Here, we report an efficient method for synthesizing these compounds without the use of transition metals. Under simple base-promoted conditions, 3-bromo-3,3-difluoroprop-1-ene reacts with N-methylanilines or N-arylacrylamides, with the elimination of one molecule of HBr, to give the target compound. Another efficient method for synthesizing difluoroalkenes is the reaction of 2-bromo-3,3,3-trifluoroprop-1-ene with indole or its analogues.

The catalytic intermolecular cyclization of thiophenols with allylic alcohols in the presence of bismuth triflate afforded the corresponding thiochromane derivatives in a one-pot reaction. The Bi(OTf)3-catalyzed reaction was also applied to the intermolecular cyclization of diaryl disulfides with 3-methylbut-2-en-1-ol to produce the corresponding thiochromanes.

A convergent approach to the forskolin skeleton is described. Assembly of a simplified tricyclic framework is achieved in a single step via the dihydropyrone Diels–Alder reaction. Selective manipulation of the resulting cycloadduct, in conjunction with an unusual equilibration of the C8 stereocenter, provides access to scaffolds that differ in relative stereochemistry at both the A/B and B/C ring junctions.

Hydrazine and its derivatives have served as a conventional bipropellant fuel for several decades. However, their extremely acute toxicity and carcinogenicity, high volatility, and environmental impact have attracted significant attention. In order to synthesize green bipropellant fuels with high density, high specific impulse, and good thermal stability, three novel N-alkyl-1,2,4-triazole–borane complexes were successfully synthesized by reacting alkylated 1,2,4-triazole coordinated with sodium borohydride in the presence of ammonium sulfate. During the droplet test with white fuming nitric acid, there was a relatively short ignition delay time of 98 ms. Additionally, these hypergolic fuels possessed a high density exceeding 1.10 g cm–3, and the specific impulse is ranging from 187 to 199 s, and the highest decomposition temperature reaches 153.4 °C. These results demonstrate their great potential as hypergolic fuels or hypergolic ionic liquid additives in the field of hypergolic materials.

A new and simple method to prepare 3-cinnamoyl-3-hydroxyphthalide derivatives from 2-hydroxy-3-methyl-1,4-naphthoquinone and substituted benzaldehydes was unexpectedly uncovered. The reaction was conveniently performed in DMSO at 100 °C with K3PO4 as a base and AlCl3 as a catalyst. We propose that the reaction proceeds by a cascade process involving nucleophilic addition followed by demethylation and rearrangement. The products were typically obtained in moderate to good yields. The highest yield (95%) was obtained when the reaction of 2-bromobenzaldehyde was performed for 24 hours. X-ray crystallography of the product derived from 2-fluorobenzaldehyde unequivocally confirmed the structure of the hydroxyphthalide derivatives.

A new type of functionalized BODIPY dyes is described. Utilizing an established procedure for Buchwald–Hartwig reactions, we have been able to convert α-chloro BODIPYs to α-azo-BODIPYs using phenylhydrazines. Optimization of the reaction conditions and variation of the BODIPY core and the phenylhydrazine were conducted. Absorption and emission spectra were recorded.

A palladium-catalyzed β-C(sp3)–H arylation of aliphatic ketones by using acetohydrazide as a transient directing group has been developed. The reaction proceeds through a less-favored [5,5]-bicyclic palladacycle intermediate and is promoted by a pyridine ligand.

An efficient and practical method for the bromination of electron-rich arenes and heteroarenes was developed by using S-methyl methanethiosulfonate as the oxidant. All the bromine atoms were basically transferred to the brominated products, demonstrating the exceptional atom economy and practicality of the proposed protocol. The method reduces the amount of bromine required for this reaction system and obtains products in moderate to good yields.

A tripeptide catalyst derived from natural l-amino acids was employed in the reaction of β-nitrostyrenes with cyclohexanone, serving as a model for the asymmetric Michael addition reaction. The reaction was conducted in the presence of H-Pro-Tle-Gly-OH and 2-fluoro-4-chlorobenzoic acid as co-catalysts (each at 20 mol%) in DMF-H2O (5:1) at 0 °C for 3 days. This process yielded the desired Michael adducts with excellent efficiency and good stereoselectivity (up to 98% yield, up to 92% ee).

Brønsted acid catalyzed intramolecular allylic substitution reaction of secondary and tertiary allylic alcohols has been developed. A variety of 2-vinylchromans were efficiently prepared in moderate to excellent yields. The given method features wide substrate scope, operational simplicity, and mild, metal-free reaction conditions. The practicability of the method was demonstrated by a gram-scale reaction and further derivations of the product. Preliminarily studies on a catalytic asymmetric reaction were also undertaken.