Stereoselective acid-catalyzed homoallylic rearrangement of cyclopropylsilylmethanols: an efficient route to Z-homoallyl derivatives

Treatment of cyclopropylsilylmethanols derived from cyclopropyl silyl ketones with acid catalyst gives the corresponding silyl-substituted homoallyl derivatives in high yields with good stereoselectivity, independent of the substituents on the cyclopropyl ring. Cyclopropylsilylmethanols having a n-, s-butyl or phenyl group on the carbinyl carbon react to afford the E-homoallyl derivatives selectively. On the other hand, the reaction of cyclopropylsilylmethanols having a tert-butyl group gives Z-isomers exclusively. The following protiodesilylation of the resulting homoallyl derivatives proceeds with retention of configuration.     

Acid-catalyzed chemodivergent reactions of 2,2-dimethoxyacetaldehyde and anilines

Chemodivergent reactions of 2,2-dimethoxyacetaldehyde and anilines were described, which were established on the basis of either a CC bond cleavage or a rearrangement process of a reaction intermediate. These reactions proceeded in a condition-determined manner with good functional group tolerance. In the first model, 2,2-dimethoxyacetaldehyde reacted with aniline to form a new CN bond, in the presence of O₂, via a CC bond cleavage reaction. However, in the second model, by performing the reaction in the absence of O₂, Heyns rearrangement occurred and generated a new CO bond to form methyl phenylglycinate. Such condition-determined reactions not only offered the new way for value-added conversion of biomass-derived platform molecule, 2, 2-dimethoxyacetaldehyde, but also provided efficient methods for the synthesis of N-arylformamides and methyl phenylglycinates.     

三甲硅基醚的断裂研究

Sommer等[1]首次应用（Me3SiO）2SO2向醇羟基引人三甲硅基（TMS）以保护羟基以来，已发展出很多方便有效的向醇羟基引人TMS保护基团的方法[2]．通常，立体阻碍越小的醇，其羟基越容易被硅基化，而且该TMS保护基团也就越容易在酸或碱性条件下被水解脱除[2]我们在天然产物PrehisPanolone的合成中[3]，羟基r-丁烯酸内酯2是一个关键的中间体．如何脱除前体三甲硅基醚的r-丁烯酸内酯1中的TMS保护基团是一个关键的问题．我们采用四了基氟化铵（TBAF）[4]（A）、酸性水解[5]（B）、碱性醇解[6]（C）和三氟化硼乙醚溶液（BF3-Et2O）[7]…     

Optimisation of a key cross-coupling reaction towards the synthesis of a promising antileishmanial compound

During the course of a research program aimed at identifying novel antileishmanial compounds, a multi-gram synthesis of N-(trans-4-((4-methoxy-3-((R)-3-methylmorpholino)-1H-pyrazolo[3,4-d]pyrimidin-6-yl)amino)cyclohexyl)-2-methylpropane-1-sulfonamide ((R)-1) was required. This letter describes optimisation of the reaction conditions and protecting group strategy for a key Buchwald-Hartwig coupling, delivering the required quantities of (R)-1, as well as further compounds in the series.     

A novel aza-Prins-Friedel-Crafts reaction for the synthesis of 4-arylpiperidines

Aldehyde, homoallylic amine and arene undergo smooth cyclization in the presence of BF₃·OEt₂ to afford 4-arylpiperidines in good yields and with high trans-selectivity. This is the first report on the preparation of 4-arylpiperidines via aza-Prins-Friedel-Crafts reaction.     

Acid-catalyzed transformation of rubrene to indenonaphthacene and its paired interacting orbital (PIO) analysis

Treatment of rubrene (5,6,11,12-tetraphenylnaphthacene) with trifluoroacetic acid in dichloromethane gives 4b,9,10-triphenyl-4b,9-dihydroindeno[1,2,3-fg]naphthacene (1) as the sole isolable product. Paired interacting orbital (PIO) analysis indicates that the reaction is initiated by preferential attack of H⁺ at C(11) position of rubrene.     

Imino-ene reaction of N-tosyl arylaldimines with α-methylstyrene: application in the synthesis of important amines

Copper(II) or tin(II) trifluoromethanesulfonate in combination with TMSCl effectively activates a C-H bond for the imino-ene reaction of N-tosylarylaldimines with α-methylstyrene. A wide variety of N-tosylarylaldimines were used to give homoallylamines in good to excellent yields under mild conditions. The imino-ene adduct was converted into a β-amino ketone. The synthesis of a 2,4-substituted pyrrolidine and a piperidine was also achieved from the imino-ene product via a Mitsunobu reaction and a Grubbs cyclization, respectively.     

Triflic acid-promoted aza-Prins-Ritter reaction sequence: a novel synthesis of 4-amidopiperidine derivatives

4-Amidopiperidine derivatives have been prepared for the first time in good yields and with high selectivity by means of aza-Prins-Ritter reaction sequence using 1.2 equiv of triflic acid under mild reaction conditions.     

1-Trimethylsilyl-, 1-Trimethylgermyl- und 1-Trimethylstannyl-3,4-dimethylphospholen

1-Trimethylsilyl-, 1-Trimethylgermyl-, and 1-Trimethylstannyl-3,4-dimethylphospholene 1-Lithium-3,4-dimethylphospholen reacts with Me₃SiCl and Me₃GeCl yielding 1-trimethylsilyl-3,4-dimethylphospholene ( 1 ) and 1-trimethylgermyl-3,4-dimethylphospholene ( 2 ) respectively. 2 and 1-trimethylstannyl-3,4-dimethylphospholene ( 3 ) are formed using the reaction of 1 with Me₃GeCl and Me₃SnCl respectively. The ¹H, ¹³C and ³¹PNMR-spectra as well as the mass spectra of the new compounds are discussed.     

Acid-catalyzed enzymatic hydrolysis of 1-methylcyclohexene oxide

Limonene-1,2-epoxide hydrolase from Rhodococcus erythropolis DCL14, an enzyme involved in the limonene metabolism of this microorganism, catalyzes the enantioselective hydrolysis of 1-methylcyclohexene oxide. (1R,2S)-1-Methylcyclohexene oxide was the preferred substrate and it was mainly hydrolyzed to (1S,2S)-1-methylcyclohexane-1,2-diol, while (1S,2R)-1-methylcyclohexene oxide was converted more slowly and mainly yielded (1R,2R)-1-methylcyclohexane-1,2-diol. The reaction proceeded with a high regioselectivity (C1:C2, 85:15). H₂¹⁸O-labelling experiments confirmed that the nucleophile was mainly incorporated at the most substituted carbon atom, suggesting that limonene-1,2-epoxide hydrolase uses an acid-catalyzed enzyme mechanism.     

A general method for synthesis of trifluoroacetyltrialkyl(aryl)silanes and the Sakurai reaction of fluorinated acylsilanes with allyl silanes

Trifluoroacetyltrialkyl(aryl)silanes, synthetic equivalents of trifluoroacetaldehyde, were prepared in good to moderate yields by reaction of 1,1-difluoro-2-trialkyl(aryl)silyl-2-trimethylsilyloxyethenes with Selectfluor^®. Sakurai reaction of fluorinated acylsilanes formed either the α-silylated ketones by means of Brook- and retro-Brook isomerization or, in the absence of Brook isomerization, homoallylic alcohols.     

Photo-Fries and Fries reaction of 5,8-dihydro-1-naphthyl esters

Systematic studies were performed on the photo-Fries and the Fries reaction of aliphatic, aliphatic unsaturated, aromatic and aromatic unsaturated esters of 5,8-dihydro-1-naphthol. The Fries reaction of 5,8-dihydro-1-naphthyl acetate in various solvents is also reported.     

Formation of trimethylsilylated open-cage oligomeric azidophenylsilsesquioxanes

Formation of open-cage oligomeric azidophenylsilsesquioxane was surprisingly discovered in the successive reduction and azidation reactions starting from octa(nitrophenyl)octasilsesquioxane. The mixture of oligomeric products was characterized after end-capping with trimethylsilyl groups. The IR spectra confirmed the introduction of azide function to aromatic moiety, and trimethylsilyl group on silsesquioxane framework. Together with the GPC result, NMR analysis revealed the introduction of different number of trimethylsilyl groups in the structure. Some of them maintained the cage-like silsesquioxane structure characterized by XRD analysis. Their TGA profiles gave a unique pattern with clear two-step mass loss with the first mass loss of about 8-10 wt% from 180 to 225 °C corresponding to a thermal decomposition of azide groups.     

Acid-catalyzed formation of free radicals in the reaction of hydroperoxides with ketones

The kinetics of formation of free radicals in the cyclohexanone (CH)-tert-butylhydroperoxide (TBHP)-para-toluenesulfonic acid (PTSA) system in acetonitrile was studied. The stoichiometry of the reaction corresponds to the consumption of two TBHP molecules per ketone molecule, whereas the yield of free radicals is -20 % based on the TBHP reacted.     

Sequential Ir‐Catalyzed Allylation/2‐aza‐Cope Rearrangement Strategy for the Construction of Chiral Homoallylic Amines†

Sequential Ir‐catalyzed asymmetric allylation/2‐aza‐Cope rearrangement of arylidene aminomalonates with allylic carbonates was successfully developed, and a variety of enantioenriched homoallylic amine derivatives were obtained in high yields with good chirality transfer and excellent E/Z‐geometry control (up to 99% yield, 96% ee). Compared with previous dual catalytic system established for this transformation, the current mono metal catalytic system provides a simpler and more practical protocol employing the readily available starting materials.     

Preparation of trimethylsilyl group containing copolymer for negative-type photoresists that enable stripped by an alkaline solution

A series of four trimethylsilyl group containing copolymers were synthesized using the solution free-radical copolymerization with azobisisobutyronitrile (AIBN) in 1,4-dioxane at 60 °C. The photoresists were prepared by dissolving copolymer, one of two kind photosensitizer (dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate) and Michler's ketone in tetrahydrofuran (THF). The cyclic maleimide group was responsible for the high thermal stabilities. After irradiation by a deep-ultraviolet light and development with mixed solvent (methyl isobutyl ketone:2-propanol=1:3), the developed patterns showed negative images and exhibited good adhesion to the silicon wafer without using any adhesion promoter. The resolution of the resists was at least 1.75 μm and the oxygen plasma etching rate was 1/6 of hard-baked HPR-204, which can be also used as the top-imaging layer of a bilayer resist for microlithographic application. These photoresists can be stripped by week alkaline solution such as sodium carbonate solution (0.01 wt.%) after exposure.