Several important reactions in organic chemistry thrive on stoichiometric formation of phosphine oxides from phosphines. To avoid the resulting burden of waste and purification, cyclic phosphine ...oxides were evaluated for new catalytic reactions based on in situ regeneration. First, the ease of silane‐mediated reduction of a range of cyclic phosphine oxides was explored. In addition, the compatibility of silanes with electrophilic halogen donors was determined for application in a catalytic Appel reaction based on in situ reduction of dibenzophosphole oxide. Under optimized conditions, alcohols were effectively converted to bromides or chlorides, thereby showing the relevance of new catalyst development and paving the way for broader application of organophosphorus catalysis by in situ reduction protocols.
Phosphole regeneration by in situ reduction of phosphole oxides was used as the basis for the development of a catalytic Appel reaction (see scheme), which transforms alcohols into bromides and chlorides with good conversions.
A novel, in‐situ synthesis of dichlorotriphenylphosphorane (Ph3PCl2) is accomplished upon combining PPh3 and the easily prepared hypervalent iodine reagent iodobenzene dichloride (PhICl2). The ...phosphorane is selectively generated in the presence of carboxylic acid or alcohol residues to rapidly produce acyl chlorides and alkyl chlorides in high yields. Addition of EtOH, PhOH, BnOH, Et2NH or CH2N2 results in the direct synthesis of esters, amides and diazo ketones from carboxylic acids.
An in‐situ synthesis of dichlorotriphenylphosphorane (Ph3PCl2) was achieved by a chlorine transfer reaction between iodobenzene dichloride (PhICl2) and PPh3. When carried out in the presence of carboxylic acids, the resulting acyl chlorides could be trapped with various nucleophiles. When carried out in the presence of alcohols, alkyl chlorides were produced.
Activation of a hydroxyl group towards nucleophilic substitution via reaction with methanesulfonyl chloride or PPh3-CBr4 system is a commonly used pathway to various functional derivatives. The ...reactions of (5R(S),6R(S))-1-X-6-(hydroxymethyl)-2,2-dimethyl- 1-azaspiro4.4nonanes 1a–d (X = O·; H; OBn, OBz) with MsCl/NR3 or PPh3-CBr4 were studied. Depending on substituent X, the reaction afforded hexahydro-1H,6H-cyclopentacpyrrolo1,2-bisoxazole (2) (for X = O), a mixture of 2 and octahydrocyclopentacazepines (4–6) (for X = OBn, OBz), or perhydro-cyclopenta2,3azeto1,2-apyrrol (3) (for X = H) derivatives. Alkylation of the latter with MeI with subsequent Hofmann elimination afforded 2,3,3-trimethyl-1,2,3,4,5,7,8,8a-octahydrocyclopentacazepine with 56% yield.
Herein, we report a green, chromatography-free Appel chlorination and bromination in both catalytic and stoichiometric form. Improved sustainability was achieved via the effective replacement of ...chlorinated solvents with dimethyl carbonate and the use of triphenylphosphine oxide (PPh3O) as a recyclable organocatalyst. The substrate scope of this halogenated solvent-free reaction was shown to be analogous to a contemporary methodology, and removal and recovery of PPh3O from the desired products were effectively demonstrated. Investigations into the catalytic cycle were conducted, and REACT-IR was demonstrated to be an effective method of reaction monitoring in situ. Optimized methodology was applied to the synthesis of 1-bromo-4-(1-bromoethyl)benzene, a key building block employed during the discovery of a GSK fatty acid synthase inhibitor.
A series of 12 new copper-based photocatalysts of the type Cu(N^N)(P^P)BF
4
were synthesized bearing π-extended diimine ligands. The complexes have red shifted absorptions and larger extinction ...coefficients than complexes prepared with a parent diimine, dmp. The complexes were evaluated for their ability to promote three different photochemical transformations. Although the complexes were inactive in a reductive PCET process, the complexes afforded good yields in both SET and ET processes. Interestingly, homoleptic copper-complexes derived from the π-extended diimines were significantly more active in SET processes than analogous complexes with simpler diimines.
Cholesterol reacts under Appel conditions (CBty/PPhj) to give 3.5-cholestadiene (elimination) and 3ß-bromocholest-5-ene (substitution with retention of configuration). Thus, the bromination of ...cholesterol deviates from the stereochemistry of the standard Appel mechanism due to participation of the A5 Tt-electrons. In contrast, the subsequent azidolysis (NaNj/DMF) of 3ß-bromocholest-5-ene proceeds predominantly by Walden inversion (Sn-) affording 3a-azidocholest-5-ene. The structures of all relevant products were revealed by X-ray single crystal structure analyses, and the NMR data are in agreement to the reported ones. In light of these findings, we herein correct the previous stereochemical assignments reported by one of us in the Beilstein J. Org. Chem. 2015. 11. 1922-1932 and the Monatsh. Chem. 2018. 149. 505-517.
Exploration of α,α-dibromo-β-dicarbonyl compounds as novel bromine agents for the conversion of alcohols to alkyl bromides under neutral conditions has been achieved. This method can be used for ...acid-sensitive substrates and allows the bromination of various primary and secondary alcohols to proceed at room temperature within a very short period of time.
Exploration of α,α-dibromo-β-dicarbonyl compounds as novel bromine agents for the conversion of alcohols to alkyl bromides under neutral conditions has been achieved. This method can be used for acid-sensitive substrates and allows the bromination of various primary and secondary alcohols to proceed at room temperature within a very short period of time.
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