Lewis acid mediated claisen-type rearrangement of aryl dienyl ethers

In the presence of BF₃·.OEt₂, aryl dienyl ethers were rearranged under mild conditions to afford dienyl phenols in good yields.     

Synthesis of disaccharides via tert-butyl ethers

Conclusions ,-Trehalose octaacetate was synthesized.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1643–1644, July, 1972.     

Synthesis of cyclic enones via direct palladium-catalyzed aerobic dehydrogenation of ketones

α,β-Unsaturated carbonyl compounds are versatile intermediates in the synthesis of pharmaceuticals and biologically active compounds. Here, we report the discovery and application of Pd(DMSO)(2)(TFA)(2) as a catalyst for direct dehydrogenation of cyclohexanones and other cyclic ketones to the corresponding enones, using O(2) as the oxidant. The substrate scope includes heterocyclic ketones and several natural-product precursors.     

Synthesis of galanthamine: Intramolecular para-ortho-coupling of diaryl ethers by anodic oxidation.

Intramolecular para-ortho-coupling of the amide 4 to 7 was achieved by anodic oxidation in acetonitrile solution (containing 2% of methanol) in eighty % yield.     

1,2-dioxines as masked cis gamma-hydroxy enones and their versatility in the synthesis of highly substituted gamma-lactones

Addition of highly stabilized ester nucleophiles to 1,2-dioxines affords good to high yields of gamma-lactones with high diastereoselectivity. Heterolytic or homolytic cleavage of the 1,2-dioxines under appropriate conditions generates the key reactive cis gamma-hydroxy enones, which ultimately afford the observed gamma-lactones. Diastereoselectivity is installed as a result of anti 1,4-addition by the ester enolate to the cis enones followed by intramolecular cyclization. The reaction is tolerant of a range of substitution patterns on the 1,2-dioxine while a broad range of esters are also accommodated. In addition to the synthesis of racemic gamma-lactones, highly enantioenriched gamma-lactones can also be synthesized when chiral cobalt(II) catalysts are employed for the initial homolytic ring-opening of the 1,2-dioxine.     

Synthesis of analogues of Eunicea gamma-cembranolides containing cyclic ethers via saponification.

A method for the synthesis of derivatives of the lead structures euniolide (1), 12,13-bisepieupalmerin (2), and eupalmerin acetate (3) containing tetrahydrofuran and tetrahydropyran ring systems was developed on the basis of alkali-induced intramolecular oxacyclizations. Representatives of the new analogues were submitted to the in vitro antitumor cell-line-screening program of the National Cancer Institute (NCI). While it was shown that a variety of structural modifications are possible, these transformations led typically to nontoxic synthetic cembranoids.     

Synthesis of anthracene ethers from anthracene methyl ethers via an acid-catalyzed exchange reaction

Selective synthesis of anthracene ethers was achieved under mild conditions via an acid-catalyzed ether-ether exchange reaction and its scope and limitations, as well as its potential in synthesizing anthracene-based crown ethers, tested.     

Synthesis of substituted thiacrown ethers via a bromoalkoxylation reaction

A variety of alkyl- or phenyl-substituted thia-crown ethers were prepared in two or three steps via bromoalkoxylation reactions of olefins. Dialkyl- and phenyl-substituted mono-and dithia-crown ethers were obtained as single compounds, whereas monoalkyl-substituted derivatives were a mixture of two positional isomers reflecting the isomeric mixture formation in the bromoalkoxylation reaction.     

Synthesis of cyclic ethers via 5-exo iodonium assisted epoxide ring expansion.

The transannular cyclization of (Z,Z)-1-hydroxy-cyclonona-2,6-diene by iodonium assisted oxirane ring expansion was studied. The regioselectivity for the [4.3.1] vs [5.2.1] 10-oxabicyclo decane skeletons is high, and the iodine addition is also highly trans-selective. The results are rationalized in terms of a tricyclic oxonium ion intermediate.     

Metal-catalyzed oxidation and epoxidation of alpha-hydroxy vinyl and dienyl sulfoxides

Treatment of acyclic alpha-hydroxyalkyl alpha,beta-unsaturated sulfoxides with t-BuOOH/VO(acac)2 results in rapid oxidation to the unsaturated sulfones followed by an unusual regio- and stereoselective epoxidation at the unsaturated sulfones; this methodology has been applied to the preparation of carbohydrate-like fragments.     

Synthesis of alpha-keto-imides via oxidation of ynamides

A de novo preparation of alpha-keto-imides via ynamide oxidation is described. With a number of alkyne oxidation conditions screened, a highly efficient RuO2-NaIO4 mediated oxidation and a DMDO oxidation have been identified to tolerate a wide range of ynamide types. In addition to accessing a wide variety of alpha-keto-imides, the RuO2-NaIO4 protocol provides a novel entry to the vicinal tricarbonyl motif via oxidation of push-pull ynamides, and imido acylsilanes from silyl-substituted ynamides. Chemoselective oxidation of ynamides containing olefins can be achieved by using DMDO, while the RuO2-NaIO4 protocol is not effective. These studies provide further support for the synthetic utility of ynamides.     

Stereo- and regioselective formation of silyl enol ethers via oxidation of vinyl anions

Oxidation of E- and Z-vinyl lithiums with silyl peroxides 5 affords silyl enol ethers 3 in good to excellent yield with retention of configuration. This methodology represents a useful new procedure for the stereo- and regioselective synthesis of ketone enolates.     

Synthesis of N-aryl-aza-crown ethers via Pd-catalyzed amination reactions of aryl chlorides with aza-crown ethers

The Pd₂(dba)₃/P(i-BuNCH₂CH₂)₃N (1) catalyst system effectively catalyzes the coupling of aza-crown ethers with electronically diverse aryl chlorides, affording N-aryl-aza-crown ethers in good yields. The Pd₂(dba)₃/P(i-BuNCH₂)₃CMe (2) catalyst system containing the more constrained bicyclic triaminophosphine is useful for aryl chlorides possessing base-sensitive ester, nitro, and nitrile functional groups.     

Synthesis of enones and butenolides using organomanganese pentacarbonyl complexes.

Sequential insertion of carbon monoxide and alkynes into alkylmanganese pentacarbonyl complexes at pressures of 6 kbar provides unsaturated manganacycles in a regioselective manner. The manganacycles can be transformed under acidic conditions into a mixture of enone and furanone. Alternatively, themanganacycle can be reduced with DIBAL-ate complex to furnish the butenolide.     

Reductive conjugate addition of haloalkanes to enones to form silyl enol ethers

A new method is presented for tandem reductive conjugate addition and silyl enol ether formation from cyclic and acyclic enones and enals in the presence of a Mn reductant, a Ni(terpyridine) catalyst, and a trialkylchlorosilane. The addition of secondary, tertiary, and hindered primary haloalkanes is demonstrated. Preliminary studies on the mechanism show that the intermediacy of L1(Ni)(η(3)-1-triethylsilyloxyalkenyl)X or in-situ-formed RMnX is unlikely.     

Synthesis of novel β-functionalized α-oximinoketones via hetero-Michael addition of alcohols and mercaptans to enones

A new methodology has been developed for the preparation of β-alkoxy and β-sulfenyl ketones by hetero-Michael addition of the corresponding alcohols and thiols to enones under acidic and basic conditions. The direct conversion of enones into β-alkoxy and β-sulfenyl α-oximinoketones was also described.