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Methylene Transfer (methylene + transfer)

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Chemistry100%

Selected Abstracts

Cycloadditions and Methylene Transfer in Reactions of Substituted Thiocarbonyl S -Methylides with Thiobenzophenone: A Computational Study

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2005
Reiner Sustmann
Abstract Regiochemistry and methylene transfer reactions in cycloadditions of aliphatic thiocarbonyl S -methylides and thiobenzophenone are analyzed by ab initio [(U)HF/3-21G*] and DFT calculations [(U)B3LYP/6-31G*//(U)HF/3-21G* and (U)B3LYP/6-31G*]. The formation of regioisomeric 1,3-dithiolanes is explained by the competition of concerted (2,4-substituted 1,3-dithiolane) and stepwise cycloaddition via C,C -biradicals (4,5-substituted 1,3-dithiolane). Aliphatic thiocarbonyl S -methylides with sterically demanding substituents undergo substantial methylene transfer in the reaction with thiobenzophenone. This process involves dissociation of the C,C -biradical intermediate with liberation of thiobenzophenone S -methylide which, in turn, combines with a second molecule of thiobenzophenone. Calculated activation parameters for the different processes are in agreement with the experimental observations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Aliphatic Thiocarbonyl Ylides and Thiobenzophenone: Experimental Study of Regiochemistry and Methylene Transfer in Cycloadditions

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2005
Rolf Huisgen
Abstract 1,3-Dipolar cycloadditions of aliphatic or alicyclic thiocarbonyl ylides 3A-D , sterically hindered at least at one terminus , with thiobenzophenone produce both regioisomeric 1,3-dithiolanes 4 and 5. According to quantum-chemical calculations (preceding paper), a concerted cycloaddition furnishing 2,4-substituted dithiolanes 4 competes with the formation of an intermediate C,C -biradical 9 which cyclizes to the more crowded 4,5-substituted dithiolanes 5. When steric hindrance of 3 increases, the cycloaddition is superseded by ,methylene transfer', i.e., the transfer of the less hindered terminus of 3E-J to the S-atom of thiobenzophenone. The thiobenzophenone S -alkylide 11, thus formed, rapidly reacts with a second molecule ofthiobenzophenone to generate the 4,4,5,5-tetraphenyl-1,3-dithiolane 12 via the highly stabilized C,C -biradical 10. Methylene transfer occurs when the cyclization of the mixed C,C -biradical 9 requires a higher activation barrier than its dissociation to aliphatic thioketone + 11; the threshold is surprisingly well reproduced by calculations. The structural assignment of sixteen 1,3-dithiolanes is based on their formation from corresponding reactant pairs as well as on 1H and 13C chemical shifts. X-ray diffraction analyses of three spiro-1,3-dithiolanes reveal the van der Waals strain in non-bonded interactions, folding angles, shearing forces, and bond lengths. Comparison of the mass spectra of many 1,3-dithiolanes allows the reconstruction of major fragmentation pathways. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Sulfonium Ylide Epoxidation Reactions: Methylene Transfer.

CHEMINFORM, Issue 35 2004
Benjamin R. Bellenie
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

Preparation of ,-Methylene Ketones by Direct Methylene Transfer.

CHEMINFORM, Issue 21 2003
J. Augusto R. Rodrigues
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

ChemInform Abstract: Unusual Methylene Transfer in Reactions of Simmons,Smith Reagent with 1,3-Diazabuta-1,3-dienes: Synthesis of Functionalized Imidazole Derivatives.

CHEMINFORM, Issue 32 2002
S. Jayakumar
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Aliphatic Thiocarbonyl Ylides and Thiobenzophenone: Experimental Study of Regiochemistry and Methylene Transfer in Cycloadditions

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2005
Rolf Huisgen
Abstract 1,3-Dipolar cycloadditions of aliphatic or alicyclic thiocarbonyl ylides 3A-D , sterically hindered at least at one terminus , with thiobenzophenone produce both regioisomeric 1,3-dithiolanes 4 and 5. According to quantum-chemical calculations (preceding paper), a concerted cycloaddition furnishing 2,4-substituted dithiolanes 4 competes with the formation of an intermediate C,C -biradical 9 which cyclizes to the more crowded 4,5-substituted dithiolanes 5. When steric hindrance of 3 increases, the cycloaddition is superseded by ,methylene transfer', i.e., the transfer of the less hindered terminus of 3E-J to the S-atom of thiobenzophenone. The thiobenzophenone S -alkylide 11, thus formed, rapidly reacts with a second molecule ofthiobenzophenone to generate the 4,4,5,5-tetraphenyl-1,3-dithiolane 12 via the highly stabilized C,C -biradical 10. Methylene transfer occurs when the cyclization of the mixed C,C -biradical 9 requires a higher activation barrier than its dissociation to aliphatic thioketone + 11; the threshold is surprisingly well reproduced by calculations. The structural assignment of sixteen 1,3-dithiolanes is based on their formation from corresponding reactant pairs as well as on 1H and 13C chemical shifts. X-ray diffraction analyses of three spiro-1,3-dithiolanes reveal the van der Waals strain in non-bonded interactions, folding angles, shearing forces, and bond lengths. Comparison of the mass spectra of many 1,3-dithiolanes allows the reconstruction of major fragmentation pathways. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Cycloadditions and Methylene Transfer in Reactions of Substituted Thiocarbonyl S -Methylides with Thiobenzophenone: A Computational Study

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2005
Reiner Sustmann
Abstract Regiochemistry and methylene transfer reactions in cycloadditions of aliphatic thiocarbonyl S -methylides and thiobenzophenone are analyzed by ab initio [(U)HF/3-21G*] and DFT calculations [(U)B3LYP/6-31G*//(U)HF/3-21G* and (U)B3LYP/6-31G*]. The formation of regioisomeric 1,3-dithiolanes is explained by the competition of concerted (2,4-substituted 1,3-dithiolane) and stepwise cycloaddition via C,C -biradicals (4,5-substituted 1,3-dithiolane). Aliphatic thiocarbonyl S -methylides with sterically demanding substituents undergo substantial methylene transfer in the reaction with thiobenzophenone. This process involves dissociation of the C,C -biradical intermediate with liberation of thiobenzophenone S -methylide which, in turn, combines with a second molecule of thiobenzophenone. Calculated activation parameters for the different processes are in agreement with the experimental observations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Efficient Catalytic Corey,Chaykovsky Reactions Involving Ketone Substrates

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010
Sarah
Abstract It has been demonstrated for the first time that a sulfide catalyst, utilised at 20,mol% loading, can promote methylene transfer to ketones in the presence of methyl triflate and an organic base. This metal-free methodology is of broad scope , both aliphatic and aromatic ketones (including trifluoromethyl ketones) can be converted to synthetically useful terminal epoxides in excellent yields at room temperature. [source]

Aliphatic Thiocarbonyl Ylides and Thiobenzophenone: Experimental Study of Regiochemistry and Methylene Transfer in Cycloadditions

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2005
Rolf Huisgen
Abstract 1,3-Dipolar cycloadditions of aliphatic or alicyclic thiocarbonyl ylides 3A-D , sterically hindered at least at one terminus , with thiobenzophenone produce both regioisomeric 1,3-dithiolanes 4 and 5. According to quantum-chemical calculations (preceding paper), a concerted cycloaddition furnishing 2,4-substituted dithiolanes 4 competes with the formation of an intermediate C,C -biradical 9 which cyclizes to the more crowded 4,5-substituted dithiolanes 5. When steric hindrance of 3 increases, the cycloaddition is superseded by ,methylene transfer', i.e., the transfer of the less hindered terminus of 3E-J to the S-atom of thiobenzophenone. The thiobenzophenone S -alkylide 11, thus formed, rapidly reacts with a second molecule ofthiobenzophenone to generate the 4,4,5,5-tetraphenyl-1,3-dithiolane 12 via the highly stabilized C,C -biradical 10. Methylene transfer occurs when the cyclization of the mixed C,C -biradical 9 requires a higher activation barrier than its dissociation to aliphatic thioketone + 11; the threshold is surprisingly well reproduced by calculations. The structural assignment of sixteen 1,3-dithiolanes is based on their formation from corresponding reactant pairs as well as on 1H and 13C chemical shifts. X-ray diffraction analyses of three spiro-1,3-dithiolanes reveal the van der Waals strain in non-bonded interactions, folding angles, shearing forces, and bond lengths. Comparison of the mass spectra of many 1,3-dithiolanes allows the reconstruction of major fragmentation pathways. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]