Synthesis of functionalized 2-(arylthio)benzoates by formal [3+3] cyclizations of 3-arylthio-1-silyloxy-1,3-butadienes with 3-silyloxy-2-en-1-ones and 1,3-diacylcyclopropanes

Functionalized 2-(arylthio)benzoates are prepared by formal [3+3] cyclizations of 3-arylthio-1-trimethylsilyloxy-1,3-butadienes with 3-silyloxy-2-en-1-ones and 1,1-diacylcyclopropanes.     

One-pot synthesis of aryl fluorides by [3+3] cyclization of 1,3-bis(silyl enol ethers) with 2-fluoro-3-silyloxy-2-en-1-ones

Functionalized aryl fluorides were regioselectively prepared by [3+3] cyclization of 1,3-bis(silyl enol ethers) with 2-fluoro-3-silyloxy-2-en-1-ones.     

Synthesis of sterically encumbered and functionalized diaryl-diazenes by formal [3+3] cyclization of 2-aryldiazenyl-3-silyloxy-2-en-1-ones with 1,3-bis(silyloxy)-1,3-butadienes

Functionalized diaryl-diazenes (azo-dyes) were regioselectively prepared by formal [3+3] cyclization of 1,3-bis(silyloxy)-1,3-butadienes with 2-aryldiazenyl-3-silyloxy-2-en-1-ones.     

Regioselective synthesis of 4-alkyl- and 4-aryl-6-(perfluoroalkyl)salicylic acid derivatives by formal [3+3] cyclocondensation of 1,3-bis(silyloxy)-1,3-butadienes with 3-silyloxy-1-(perfluoroalkyl)prop-2-en-1-ones

4-Alkyl- and 4-aryl-6-(perfluoroalkyl)salicylic acid derivatives were regioselectively prepared by [3+3] cyclization of 1,3-bis(silyl enol ethers) with 3-silyloxy-1-(perfluoroalkyl)prop-2-en-1-ones.     

Regioselective synthesis of 2-acetyl- and 2-alkoxycarbonyl-3-(trifluoromethyl)phenols by [3+3] cyclization of 1,3-bis-silyl enol ethers with 4-ethoxy- and 4-silyloxy-1,1,1-trifluoroalk-3-en-2-ones

2-Acetyl- and 2-alkoxycarbonyl-3-(trifluoromethyl)phenols were prepared by [3+3] cyclization of 1,3-bis-silyl enol ethers with 4-ethoxy- and 4-silyloxy-1,1,1-trifluoroalk-3-en-2-ones.     

Synthesis of 3-aryl-3,4-dihydroisocoumarins by regioselective domino ‘[3+3] cyclization/lactonization’ reactions of 1,3-bis-(silyloxy)-1,3-butadienes with 1-hydroxy-5-silyloxy-4-en-3-ones

The [3+3] cyclization of 1,3-bis(silyloxy)-1,3-butadienes with 1-hydroxy-5-silyloxy-4-en-3-ones afforded 6-(2-aryl-2-chloroethyl)salicylates, which were transformed into 3-aryl-3,4-dihydroisocoumarins by silica gel-mediated lactonization.     

Synthesis of dibenzo[b,d]pyran-6-ones based on [3 + 3] cyclizations of 1,3-bis(silyl enol ethers) with 3-silyloxy-2-en-1-ones

Functionalized dibenzo[b,d]pyran-6-ones were prepared by formal [3 + 3] cyclization of 1,3-bis(silyl enol ethers) with 3-silyloxy-2-en-1-ones or 1,1-diacetylcyclopropane to give functionalized salicylates, Suzuki cross-coupling reactions of the corresponding triflates, and subsequent BBr3-mediated lactonization. A second approach to dibenzo[b,d]pyran-6-ones relies on the [3 + 3] cyclization of 1,3-bis(silyl enol ethers) with 1-(2-methoxyphenyl)-1-(trimethylsilyloxy)alk-1-en-3-ones and subsequent BBr3-mediated lactonization.     

Synthesis of 1-alkoxy-3-(2-hydroxyethyl)-1-triazene 2-oxides

Synthetic procedure to access the first representatives of a new series of 3-monosubstitued functional derivatives of 1-alkoxy-1-triazene 2-oxides, i.e., 1-alkoxy-3-(2-hydroxyethyl)- and 1-alkoxy-3-(2-acetoxyethyl)-1-triazene 2-oxides, were elaborated. 1-Alkoxy-3,3-bis(2-hydroxyethyl)-1-triazene 2-oxides were used to derive 3-(2-acetoxyethyl)-, 3-(2-bromoethyl)- and 3-(2-cyanoethyl)substituted 1-alkoxy-3-(2-acetoxyethyl)-1-triazene 2-oxides.     

2-silyloxy-1,2-oxazines, a new type of acetals of conjugated nitroso alkenes

3-alkyl-substituted 1,2-oxazine N-oxides 2 can be selectively transformed into 2-silyloxy-1,2-oxazines 1 upon treatment with silylating reagents. In the solid state derivatives 1 adopt a chair conformation with the pyramidal nitrogen atom, whereas in solution they exist as an equilibrating mixture of two conformers (DeltaG++ 55-60 kJ/mol). A preliminary study of the reactivity of nitrosals 1 has shown that they react with O- and N-stabilized carbocations to yield 1,2-oxazine N-oxides with a functionalized alkyl substituent at the 3-position. Moreover, compounds 1 can rearrange into silyloxy-1,2-oxazines 5 and react with morpholine to produce 3-morpholinoalkyl-1,2-oxazines 7 existing in a tautameric equilibrium with open-chain oximes 6.     

Enantio- and diastereoselective hetero-Diels-Alder reactions between 2-aza-3-silyloxy-1,3-butadienes and aldehydes catalyzed by chiral dirhodium(II) carboxamidates

The first catalytic asymmetric hetero-Diels-Alder reaction between 2-aza-3-silyloxy-1,3-butadienes and aldehydes is described. With dirhodium(II) tetrakis[N-benzene-fused-phthaloyl-(S)-piperidinonate], Rh(2)(S-BPTPI)(4), the cycloaddition reaction proceeded exclusively in an endo mode to give all-cis-substituted 1,3-oxazinan-4-ones in high yields with up to 98% ee.     

Alkylation of 1-alkoxy-3-methyl-1-triazene 2-oxide sodium salts

1-Alkoxy-3-methyl-1-triazene 2-oxide sodium salts react with chloromethyl methyl sulfide to give a mixture of 1-alkoxy-3-methyl-3-(methylthiomethyl)-1-triazene 2-oxides and 3-alkoxy-1-methyl-3-(methylthiomethyl)-1-triazene 2-oxides. The reaction of these triazene oxide sodium salts with 3,3-dialkyl-1-chloromethoxy-1-triazene 2-oxides produces a complex mixture of product bearing the oxytriazene moieties of the starting alkoxy-1-triazene 2-oxides bonded with the methylene group as a key structural fragment.     

Photochemical and thermal addition of alcohols to 2-cyanofuran : 1-alkoxy-2-cyanocyclopropane-3-carboxaldehydes; 2-alkoxy-3-cyano-2, 3-dihydrofuran; 1-alkoxy-1-(2-furan)-methylenimine; photochemical ring contraction; cis-trans-isomerization of dihydrofurans

The photolysis of 2-cyanofuran in alcohols yields 1-alkoxy-2-cyanocyclopropane-3-carboxaldehydes as the major products, which rearrange thermally to trans-2-alkoxy-3-cyano-2,3-dihydrofurans and small amounts of cis-isomers. Thermal mutual rearrangements between trans- and cis-2- alkoxy-3-cyano-2, 3-dihydrofurans were studied. Liquid phase thermal addition of alcohols in a temperature range between 100° and 200° yields 1-alkoxy-1-(2-furan)-methylenimines, which rearrange photochemically to 2-furyl-methylamino-ketone in case of the methoxy derivative. 3-Cyano-furan does not yield photoaddition or thermal addition products. The different behaviors of 2- and 3-substituted furans are discussed.     

Reactivity of 3-silyloxy-1,4-enynes: Gold(III)-catalyzed regioselective nucleophilic substitution

Gold-catalyzed reactions of 3-silyloxy-1,4-enynes with alcohols afford primary, secondary, and tertiary pent-2-en-4-ynyl ethers in moderate to excellent yields. The substitution proceeds with high regioselectivity. An initial cyclization providing five-membered carbocycles instead was not observed under the reaction conditions. Control experiments show that these reactions are also catalyzed by Brønsted- and Lewis-acids, although scope and yields are markedly reduced.     

Efficient and practical synthesis of both enantiomers of 6-silyloxy-3-pyranone derivatives

Lipase catalyzed kinetic resolution of racemic cis-6-(tert-butyldimethylsilyloxy)-3,6-dihydro-2H-pyran-3-ol (rac)-1 was achieved in high enantiomeric excess. Transesterification of (rac)-1 with vinylacetate in ^tBuOMe yielded the alcohol (3S,6R)-1 in 99.0% ee, whereas (3R,6S)-1 was obtained, in 99.0% ee, by the lipase catalyzed ester hydrolysis of acetate (3R,6S)-2, which was obtained along with the transesterification. Both (3S,6R)-1 and (3R,6S)-1 were subjected to oxidation to provide the corresponding 6-silyloxy-3-pyranone (6R)-3 and (6S)-3, respectively. Application to the synthesis of 7, which is the key intermediate of asymmetric synthesis of pseudomonic acid A 9 is also described.     

A tandem Diels–Alder/Mannich approach to the synthesis of AE and ABE ring analogues of Delphinium alkaloids

The one-pot TiCl₄ catalysed Diels–Alder/Mannich reaction of α-cyanoaminoacrylates with 2-silyloxy-1,4-butadienes gives 6-keto-3-azabicyclo[3.3.1]nonane-1-carboxylates. Reduction of the ketone and alkylation of the resultant alcohol gives 6-alkoxy-3-azabicyclo[3.3.1]nonanes mimicking the AE rings of a number of Delphinium and Aconitum alkaloids, with the same stereochemistry as the natural products.     

O-Alkylation of 3-hydroxy-1-phenyl-2-pyrazolin-5-one

3-Hydroxy-1-phenyl-2-pyrazolin-5-one 1 reacts with primary, secondary and allylic alcohols under catalytic acidic conditions and in the presence of 3 Å molecular sieves, to afford 3-alkoxy-1-phenyl-2-pyrazolin-5-ones 3 .     

1-Trimethoxysilylmethyl-and 1-(2,8,9-trioxa-5-aza-1-silabicyclo[3.3.3]undecan-1-ylmethyl)-1,1-dimethyl-2-(3-alkoxy-3-oxopropyl)hydrazinium halides

Previously unknown 1,1-dimethyl-1-trimethoxysilylmethyl-2-(3-alkoxy-3-oxopropyl)hydrazinium and 1,1-dimethyl-1-(2,8,9-trioxa-5-aza-1-silabicyclo[3.3.3]undecan-1-ylmethyl)-2-(3-alkoxy-3-oxopropyl)-hydrazinium halides were synthesized, and physiological activity of 2-(3-ethoxy-3-oxopropyl)-1,1-dimethyl-1-(2,8,9-trioxa-5-aza-1-silabicyclo[3.3.3]undecan-1-ylmethyl)hydrazinium chloride and bromide was studied.     

Some properties of 2-alkoxy-1-alken-3-ols

Conclusions The reaction of 2-alkoxyacroleins with Grignard reagent gave some new 2-alkoxy-1-alken-3-ols, which in the presence of p-toluenesulfonic acid are cyclodimerized to 2,3,5,6-tetraalkyl-2,5-dialkoxy-1,4-dioxanes, which tend to cleave ethanol to give 2,3,5,6-tetraalkyl-5-alkoxy-1,4-dioxenes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2534–2538, November, 1980.The authors express their gratitude to V. I. Lavrent'ev and V. Yu. Vitkovskii for taking the mass spectra.     

Reactions of chloromethoxy-substituted 3-(2-acetoxyethyl)-1-hydroxytriaz-1-ene 2-oxides with 1-alkoxy-3-(2-hydroxyethyl)triaz-1-ene 2-oxide alkali salts

Reactions of 1-alkoxy-3-(2-hydroxyethyl)triaz-1-ene 2-oxides and 1-chloromethoxytriaz1-ene 2-oxides with chloromethoxy derivatives of 3-alkyl-3-(2-acetoxyethyl)- and 3,3-bis(2-acetoxyethyl)-1-hydroxytriaz-1-ene 2-oxides result in very complex product mixtures with the major product comprising the starting salt fragments linked by a methylene bridge. In these products, the central methylene group bridges either two oxygen atoms or two nitrogen atoms, or one oxygen and one nitrogen atom. The synthesized compounds contain from two to four 2-hydroxyethyl moieties.     

Novel diastereoselective synthesis of bicyclic beta-lactams through radical cyclization and their reduction toward 2-(1-alkoxy-2-hydroxyethyl)piperidines and 2-(1-alkoxy-2-hydroxyethyl)azepanes

1-Allyl- and 1-(3-phenylallyl)-substituted 4-(2-bromo-1,1-dimethylethyl)azetidin-2-ones were transformed into 3-substituted 7-alkoxy-5,5-dimethyl-1-azabicyclo[4.2.0]octane-8-ones through radical cyclization by means of n-tributyltin hydride and AIBN in toluene with excellent diastereocontrol (>or=99%). The radical cyclization of 4-(2-bromo-1,1-dimethylethyl)-1-(2-methylallyl)azetidin-2-ones afforded 8-alkoxy-3,6,6-trimethyl-1-azabicyclo[5.2.0]nonan-9-ones in good diastereomeric excess (75-78%). The reductive ring opening of 1-azabicyclo[4.2.0]octane-8-ones and 1-azabicyclo[5.2.0]nonan-9-ones with lithium aluminum hydride resulted in novel 2-(1-alkoxy-2-hydroxyethyl)piperidines and -azepanes, which were isolated as single isomers.