Utilization of 1-oxa-2,2-(dimesityl)silacyclopentane acetals in the stereoselective synthesis of polyols

We have developed a route for the stereoselective synthesis of 1-oxa-2,2-(dimesityl)silacyclopentane acetals, intermediates in the synthesis of highly functionalized 1,3-diols. This route involves a diastereoselective conjugate addition reaction of a hydrosilyl anion, a subsequent diastereoselective enolate alkylation, and a fluoride-catalyzed intramolecular hydrosilylation reaction to afford the oxasilacyclopentane acetal. A highly selective nucleophilic substitution reaction, followed by oxidation of the C-Si bond, leads to the desired polyol.     

Quinine as an organocatalytic dual activator for the diastereoselective synthesis of spiro-epoxyoxindoles

A highly efficient organocatalytic approach has been developed for the diastereoselective epoxidation of (E)-3-ylidene-indolin-2-one derivatives using readily available natural product quinine and urea-hydrogen peroxide (UHP) in DCM at 10 °C to afford trans spiro-epoxyoxindoles which were further utilized to obtain β-hydroxy-α-amino esters by water mediated regioselective ring opening from the less hindered end with aniline derivatives, under sonication.     

A diastereoselective approach for an asymmetric synthesis in pinnaic acid series

An enantiopure spiran-bearing advanced intermediate in pinnaic acid series was obtained in 11 steps starting with CN(R,S) building block.     

A rapid means for the synthesis of aldehyde acetals

Conclusions A convenient rapid method has been proposed for the acetalization of aldehydes by ethyl orthoformate in the presence of trace amounts of perchloric acid.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 921–923, April, 1986.     

Ammonium ylides for the diastereoselective synthesis of glycidic amides

A highly trans-selective protocol for the synthesis of glycidic amides was developed. This approach gave access to oxiranes by reacting stabilised ammonium ylides bearing an α-carbonyl group and aromatic aldehydes in moderate to good yields.     

Diastereoselective nucleophilic substitution reactions of oxasilacyclopentane acetals: application of the "inside attack" model for reactions of five-membered ring oxocarbenium ions

The additions of nucleophiles to oxocarbenium ions derived from oxasilacyclopentane acetates proceeded with high diastereoselectivity in most cases. Sterically demanding nucleophiles such as the silyl enol ether of diethyl ketone add to the face opposite the C-2 substituent. These reactions establish the syn stereochemistry about the newly formed carbon-carbon bond. Small nucleophiles such as allyltrimethylsilane do not show this same stereochemical preference: they add from the same face as the substituent in C-2-substituted oxocarbenium ions. The stereoselectivities exhibited by both small and large nucleophiles can be understood by application of the "inside attack" model for five-membered ring oxocarbenium ions developed previously for tetrahydrofuran-derived cations. This stereoelectronic model requires attack of the nucleophile from the face of the cation that provides the products in their lower energy staggered conformations. Small nucleophiles add to the "inside" of the lower energy ground-state conformer of the oxocarbenium ion. In contrast, sterically demanding nucleophiles add to the inside of the envelope conformer where approach is anti to the C-2 substituent of the oxocarbenium ion, regardless of the ground-state conformer population.     

Palladium-catalyzed annulation reactions for diastereoselective cyclopentene synthesis

Palladium-catalyzed annulation reactions of conjugate acceptors and allenyl boronic ester provide substituted cyclopentenes in high yields and, where applicable, diastereoselectivities. This method provides rapid assembly of building blocks for natural product synthesis, including polycyclic lactone and lactam products. Reactions are hypothesized to initiate by conjugate addition of a nucleophilic propargylpalladium complex.     

The synthesis of acetylenic acetals

Zinc chloride on silica gel is an active catalyst for the condensation of ethyl orthoformate with terminal acetylenes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1172–1173, May, 1990.     

Cyclic acetals in the synthesis of polyoxamacrocycles

Russian Chemical Bulletin - A selective one-pot procedure to access 8-, 9-, and 10-membered polyoxacycles bearing ester functions was elaborated. The procedure involved the copper-promoted...     

A new method for the synthesis of bicyclic pyran acetals

cis‐Fused bicyclic acetals were obtained from the unusual cyclization reaction between diols and dihydropyran. Furothiopyran, substituted pyranopyrans, and pyranooxepine and pyranobenzoxepine compounds were obtained with high diastereoselectivity and cis‐diastereomers were obtained in high yields.     

Novel synthesis and application of mixed acetals (acetyl methyl acetals)

A novel synthetic method for mixed acetals (acetyl methyl acetals) by electrolysis of hemithioacetals derived from methoxy- (phenylthio)methane is newly developed. Synthetic application of these mixed acetals as an aldehyde equivalent is also demonstrated.     

Amide acetals in the synthesis of pyridothienopyrimidines

Methyl 3-amino-4-arylaminothieno[2,3-b]pyridine-2-carboxylates containing various substituents in the benzene ring were synthesized by the Thorpe-Ziegler reaction of 4-arylamino-2-chloropyridine-3-carbonitriles with methyl thioglycolates. The influence of the substituent in the benzene ring, acetal structure, the solvent and the process temperature on the reactions of obtained compounds with amide acetals was studied. It was established that reactions with dimethylacetamide dimethylacetal in toluene smoothly results in amidine derivatives, viz., methyl 4-arylamino-3-[1-(dimethylamino)ethylidene]aminothieno[2,3-b]pyridine-2-carboxylates, regardless of the substituent in the benzene ring. Analogous reaction of p-fluoroderivative with dimethylacetamide dimethylacetal in refluxing anhydrous ethanol leads to intramolecular cyclocondensation to produce substituted pyridothienopyrimidines, viz., 5H-1-thia-3,5,8-triazaacenaphthenes, in good yields. Amidine derivatives were the major products in the case of the coupling of aminothienopyridines with dimethylformamide dimethylacetal under the same conditions. A new approach to the synthesis of substituted pyridothienopyrimidines, viz., 3H-1-thia-3,5,8-triazaacenaphthylenes, based on the prolonged heating of methyl 4-arylamino-3-[1-(dimethylamino)ethylidene]aminothieno[2,3-b]pyridine-2-carboxylates in the excess of acetic anhydride was elaborated. Putative mechanisms of the processes concerned are given.     

Highly diastereoselective synthesis of anti-gamma-N-benzylamino-beta-hydroxyphosphonates

The reduction of gamma-N-benzylamino-beta-ketophosphonates derived from readily available amino acids can be carried out stereoselectively with Zn(BH(4))(2) at -78 degrees C to produce the anti-gamma-amino-beta-hydroxyphosphonates.     

Regio- and diastereoselective synthesis of bifunctionalized limonenes

High regio- and diastereoselective ring opening of limonene aziridines with a variety of nucleophiles is described. The resulting novel chiral derivatives are readily accessible from limonene aziridine in either enantiomeric form in 35-94% yield.     

Enantio- and diastereoselective synthesis of erysulfone and erysulfoxide

The natural products erysulfone (1) and erysulfoxide (2) have been prepared from (+)-muconolactone (3). This synthetic work has substantiated the earlier, probable assignment of absolute configuration of these targets.