An Efficient Stereoselective Synthesis of Fluorinated Trisubstituted Alkenes

Synthesis of Trisubstituted Alkenes Bearing a Quaternary Carbon by Lewis-Acid Catalyzed Regioselective Reaction of Internal Alkynols with 2-Pyrrolylanilines

Substituted alkenes, crucial in organic chemistry, are typically accessed from internal alkynes by using transition-metal catalysis. Herein, we report a novel approach to the Lewis acid-catalyzed synthesis of trisubstituted alkenes bearing a quaternary carbon from internal alkynols and 2-pyrrolyl arylamines. This method involves allene formation followed by intramolecular [5 + 1] annulation to furnish a diverse range of trisubstituted alkenes with excellent regioselectivity and poor diastereoselectivity. Further, we demonstrated the gram-scale synthesis and synthetic transformations and proposed the reaction mechanism based on the isolation of intermediates.

Abnormal Michael Reaction: Condition-Dependent Product Distributions in the Michael Reaction of Monoalkyl-Substituted Malonates

The abnormal Michael reaction reported by Thorpe and Michael in 1900, which involves the transfer of an activating group from a nucleophilic species to an α-carbon of the Michael acceptor in reaction with monosubstituted malonates, was revisited using prototypical substrates for both intramolecular and intermolecular reactions. In both reactions, condition-dependent product distributions were observed. Thus, under the conditions using NaHMDS or NaH in THF or Et2O, no formation of the abnormal Michael product was observed, and the major product was an apparent retrograde Michael reaction in the abnormal Michael product resulting from an elimination of a malonate anion with the migrated acyl group as a part of it. The use of a base capable of generating a proton source such as NaOEt resulted in formation of the abnormal Michael product in the intermolecular reaction, although the retrograde Michael product was still a major product. On the other hand, in the intramolecular reaction, the abnormal product was not detected under any conditions used. A plausible reaction mechanism in which the lower kinetic acidity of the malonate proton compared to the thermodynamic acidity plays a significant role has been proposed.

Modified Julia fluoroolefination: selective preparation of fluoroalkenoates

The modified Julia olefination reaction has been applied to develop a stereoselective synthesis of fluoroalkenoate derivatives from a fluorobenzothiazolyl sulfone and aldehydes or a ketone. The olefination reaction can be achieved by using a variety of bases. DBU and DBU in the presence of MgBr2 were found to be the most efficient systems to prepare either (Z)- or (E)-alkenoates in moderate to excellent stereoselectivity.

Stereocontrolled Synthesis of β-Difluoromethylated Materials

Investigation of synthetic routes for regio- and stereocontrolled fluorinated materials with a difluoromethyl group, using ethyl bromodifluoroacetate as a starting material, is described. In particular, (E)-difluoromethylated trisubstituted olefins were prepared via the proton migration reaction catalyzed by using fluoride anion. Further, optically active beta-difluoromethyl esters were obtained by the enzymatic resolution.

Syntheses of α-Fluoro-α,β-unsaturated Thioamides and Thiazolines from a Fluorophosphonodithioacetate

A high-yielding synthesis of methyl fluoro(diethoxyphosphono)dithioacetate starting from its difluorinated analogue is reported. Fluorophosphonothioacetamides and -methylthiazolines, prepared from this new dithioester, have been successfully transformed into highly functionalized fluoroalkenes. Good stereoselectivity in favor of the E isomer was observed from the fluorophosphonomethylthiazolines. The potential of these new fluorinated olefinating reagents for the synthesis of modified peptides and glycosides is also disclosed.

The synthesis of homoallylic amines utilizing a cuprate-based 1,2-metalate rearrangement

Lithiation of the N-2,4,6-triisopropylbenzenesulfonyl-2-pyrroline (16) and treatment of the resulting cyclic vinyllithium reagent with R2CuCNLi2 produced an acyclic vinyl organometallic species that, when treated with an electrophile (H2O or RX), gave the homoallylic sulfonamides 18a-k in 37-93% yields and in > 95% diastereoselectivity. The deprotection of a representative homoallylic sulfonamide 18d was achieved in 83% yield by sonication in the presence of lithium wire and catalytic 4,4'-di-tert-butylbiphenyl (DBB). The efficacy of this general procedure for the production of homoallylic amine derivatives is demonstrated by the preparation of the diene amine 25, a key intermediate in the synthesis of a squalene synthetase inhibitor.

Bis(2,2,2-trifluoroethyl)bromophosphonoacetate, a Novel HWE Reagent for the Preparation of (E)-alpha-Bromoacrylates: A General and Stereoselective Method for the Synthesis of Trisubstituted Alkenes

A novel reagent, methyl bis(2,2,2-trifluoroethoxy)bromophosphonoacetate (3a), was designed and prepared in order to efficiently synthesize (E)-alpha-bromoacrylates, which are useful precursors for various C-C bond formations. Honer-Wadsworth-Emmons (HWE) reaction of various aldehydes with 3a in the presence of t-BuOK and 18-C-6 gave the corresponding (E)-alpha-bromoacrylate derivatives with high stereoselectivity. Using the (E)-alpha-bromoacrylate as a key intermediate, a general stereoselective synthesis of trisubstituted alkenes via Pd-catalyzed cross-coupling was developed.

Synthesis of trisubstituted alkenes via olefin cross-metathesis

[formula: see text] Trisubstituted alkenes have been prepared for the first time via intermolecular olefin cross-metathesis, using 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene ruthenium alkylidene complexes 3a,b in good yields with moderate E selectivity. In addition, protected alcohols near the geminal disubstituted olefin improve reactivity for cross-metathesis.

Synthetic Applications of the Carbanion with a Fluoroalkyl Group Generated by Palladium(0) Catalyst under Neutral Conditions

The generation and synthetic application of stable carbanions situated in the beta position from fluorine atom(s) are described. Palladium(0)-catalyzed allylation reactions under neutral conditions proceeded smoothly in the system where a methylene group is activated by fluoroalkyl and carbonyl groups. In the above systems, the 2,2,2-trifluoroethyl moiety has been introduced onto the allylic position without the release of fluoride. Further, palladium(0)-catalyzed heterocyclization was achieved from the reaction of vinyl epoxide with 2-(trifluoromethyl)acrylate and/or 2,3,3,3-tetrafluoropropionate.