A new mechanism for the Favorskii rearrangement

The title reaction was investigated by the use of ONIOM-RB3LYP calculations. A reaction system composed of alpha-chlorocyclohexanone, a methoxide ion and 8 MeOH solvent molecules was adopted. Two reaction channels, the semibenzilic acid mechanism (A) and cyclopropanone mechanism (B), were compared. B is found to be more favorable than A. The rate-determining step of B is the (MeOH)(3) addition transition state (TS3B) to the cyclopropanone intermediate. While TS3B involves a concerted function of MeO(-) addition and proton relays, it has a large activation energy. A new route was found, where the chloride ion evolved at the cyclopropane formation step (TS2B) works as a nucleophile to the cyclopropanone intermediate. Thus, a cyclopentane-carbonyl chloride intermediate is formed with a small activation energy. A new cyclopropanone mechanism is proposed.     

Favorskii rearrangement of a highly functionalized meso-dihaloketone

This paper describes studies on the feasibility of an asymmetric Favorskii rearrangement of a meso-dihaloketone substrate. In the racemic series, metal amide bases in the presence of amines give poor to reasonable yields of ring-contracted unsaturated cyclopentyl amides, whilst amines in aqueous solvent mixtures afford cyclopentyl amides in good to excellent yields. A range of chiral non-racemic amines are screened, a tiny diastereo-bias is observed and a tentative mechanistic rationale for the diastereoselective process is proposed.     

Favorskii rearrangement of α,β-epoxy ketones

Reactions of α,β-epoxy ketones with nucleophilic bases generally take one of two courses: (1) α-displacement followed by β-elimination of water or (2) Favorskii rearrangement via a cyclopropanone or zwitterion intermediate. Among the factors that appear to control these reactions, it is suspected that an α′-substituent effect may operate. Such an effect has been confirmed by observing the conversion of 3,5,5,6 - tetramethyl - 2,3 - epoxycyclohexanone (1) to the ring-contracted γ-lactone 3, together with other Favorskii rearrangement products, on treatment with refluxing methanolic potassium hydroxide. The α′-methyl substituted steroid 2 under similar reaction conditions was transformed into roughly equal amounts of 4, 5 and 4 (all rationalized by a Favorskii-like mechanism). In each case the analogous epoxy ketone lacking an α′-Me substituent failed to give any Favorskii products.     

Favorskii rearrangement of 23-oxo-3-epi-smilagenin acetate induced by iodosobenzene

Treatment of (25R)-3α-acetoxy-5β-spirostan-23-one with diacetoxyiodobenzene in KOH/MeOH led to F-ring contraction via Favorskii rearrangement.     

A convenient preparation of 3-methyl-3,4-dihydro-2(1H)-quinazolinone

3-Methyl-3,4-dihydro-2(1H)-quinazolinone ( 5 ) can be prepared in good yield and quality from o-nitrobenzyl chloride ( 1 ). The three-step sequence requires no purification of intermediates or final product.     

A convenient preparation of aryltrifluoromethylketones

The reaction of aryllithium reagents prepared by halogen metal exchange or direct metallation with α,α,α-trifluoro-N,N-dimethylacetamide give the corresponding aryltrifluoromethylketones in good yield.     

A convenient preparation of indoline

An efficient method for chemically reducing indole to indoline using zinc dust and 85% phosphoric acid is described. 2, 3-Dimethylindole, 1,2,3, 4-tetrahydrocarbazole and N-methyl-l,2,3,4-tetrahydrocarbazole are also reduced to the corresponding dihydroindoles in somewhat lower yields. Unlike earlier acid-metal reductions of indole little or no polymerization is observed.     

A convenient synthesis of sulfonylureas from carboxylic acids and sulfonamides via an in situ Curtius rearrangement

A one-pot reaction of carboxylic acids with sulfonamides to afford sulfonylureas is described.     

A convenient preparation of 2-fluoro-3-alkoxy-1,3-butadienes

[reaction: see text] 1-Chloro-1-fluoro-2-methoxy-2-methylcyclopropane eliminates HCl on heating in quinoline solution above 50 degrees C to give 2-fluoro-3-methoxy-1,3-butadiene in high yield. If an alcohol is added to the reaction then a 2-fluoro-3-alkoxy-1,3-butadiene is obtained in high yield. The dienes give smooth 4 + 2 cycloaddition reactions.     

A convenient preparation of xanthene dyes

A facile synthetic route utilizing readily available reagents affords a series of regioisomerically pure xanthene dye derivatives. Advantages include relatively mild conditions and good to excellent yields. Nonpolar, highly crystalline intermediates are isolable by standard chromatographic techniques. The intermediates are in the requisite xanthene oxidation state, thus avoiding the need for relatively inefficient oxidation chemistry and/or harsh conditions. During the course of this work, a new boron-mediated 1,2-aryl migration reaction was discovered.     

A convenient preparation of deuterated fluoroolefins

The reduction of iodo-containing fluoroolefins with NaAlH₄ in diglyme followed by hydrolysis with D₂O provides a convenient preparative procedure to the corresponding deuterated fluoroolefin.     

A convenient high-yield preparation of phenylfluoroboranes

Phenylfluoroboranes were conveniently prepared in near-quantitive yield from the corresponding haloboranes (chloro- and bromo-) and inexpensive alkali-metal salts of perfluorinated complex anions in the absence of any solvent.     

A convenient synthesis of pseudoglycosides via a Ferrier-type rearrangement using metal-free H3PO4 catalyst

A mild and efficient synthesis of pseudoglycals has been developed using a metal-free catalytic system. Phosphoric acid proved to be an excellent catalyst for conversion of 2,4,6-tri-O-acetyl-d-glycal to 2,3-unsaturated O-glycosides. A wide range of alcohols including naturally bioactive compounds could be coupled with the glycal to give the desired products in good to excellent yields and with high levels of α-selectivity.     

Gas‐phase synthesis of hydrodiphenylcyclopropenylium via nonclassical Favorskii rearrangement from alkali‐cationized α,α′‐dibromodibenzyl ketone

The gas‐phase synthesis of hydrodiphenylcyclopropenylium from alkali‐cationized α,α′‐dibromodibenzyl ketone (1) via nonclassical Lewis‐acid‐induced Favorskii rearrangement has been studied by electrospray ionization/tandem mass spectrometry (ESI‐MS/MS) and theoretical methods, showing that cations [1–Br]⁺ by debromination from 1 and 1 · M⁺(M = Li or Na) by alkali‐metal cationization of 1 could convert into the protonated diphenylcyclopropenone 2 · H⁺ by collision‐induced dissociation in the gas phase. A concerted mechanism for the Lewis‐acid‐induced Favorskii rearrangement from alkali‐metal‐cationized α,α′‐dibromodibenzyl ketone was proposed and studied, based on mass spectrometric results and theoretical methods. Copyright © 2010 John Wiley & Sons, Ltd.     

A convenient preparation of mixed thexyldialkylorganoboranes

Thexylborane can be treated consecutively with different halomagnesium dialkylcuprates or lithium dialkyl cuprates to afford the corresponding totally mixed thexyldialkyl organoborane.     

A convenient preparation of 3-substituted furans: synthesis of perillene and dendrolasin

A variety of 3-substituted furans, including the natural products perillene and dendrolasin, are obtained in good yield via reductive annulation of 1,1,1-trichloroethyl propargyl ethers using catalytic Cr(II) regenerated by Mn/TMSCl. [reaction: see text]