Shigekazu Ito - Academia.edu (original) (raw)

Papers by Shigekazu Ito

Research paper thumbnail of Synthesis, Structure, and Reactivity of Novel 3,4-Diphosphacyclobutenes Bearing Silyl Groups

The Journal of Organic Chemistry, 2005

X-ray crystallography for 5b and 10. A Rigaku RAXIS-IV imaging plate detector with graphite-monoc... more X-ray crystallography for 5b and 10. A Rigaku RAXIS-IV imaging plate detector with graphite-monochromated Mo K α radiation (= 0.71070 Å) was used. The structure was solved by direct methods (SIR92), 1 expanded using Fourier techniques (DIRDIF94), 2 and then refined by full-matrix least squares. Structure solution, refinement, and graphical representation were carried out using the teXsan package. 3

Research paper thumbnail of Modeling the Direct Activation of Dihydrogen by a P2C2 Cyclic Biradical: Formation of a Cyclic Bis(P−H λ5-phosphorane)

Inorganic Chemistry, 2009

The synthesis of a remarkable cyclic bis(P-H lambda(5)-phosphorane) is reported. A stable phospho... more The synthesis of a remarkable cyclic bis(P-H lambda(5)-phosphorane) is reported. A stable phosphorus-heterocyclic biradical, 1,3-diphosphacyclobutane-2,4-diyl, sequentially accepts negatively and positively charged hydrogen atoms to afford 2,4-diphospha-1,3-cyclobutadiene with a diylidic structure containing two P-H bonds.

Research paper thumbnail of Unique molecular distortion in the 2,4,6-tri-t-butylphenyl group

Arkivoc, 2011

X-ray structure of a stable chlorophosphine and a secondary phosphine both bearing one or more st... more X-ray structure of a stable chlorophosphine and a secondary phosphine both bearing one or more sterically bulky 2,4,6-tri-t-butylphenyl (Mes*) group(s) are discussed in terms of molecular distortion. Steric encumbrance of the bulky aromatic ring induces a boat-type structure of the six-membered aromatic ring, and the degree of distortion depends on a substituent in the ipso position.

Research paper thumbnail of Direct α-Siladifluoromethylation of Lithium Enolates with Ruppert-Prakash Reagent via CF Bond Activation

Chemistry - A European Journal, 2014

The direct a-siladifluoromethylation of lithium enolates with the Ruppert-Prakash reagent (CF 3 T... more The direct a-siladifluoromethylation of lithium enolates with the Ruppert-Prakash reagent (CF 3 TMS) is shown to construct the tertiary and quaternary carbon centers. The Ruppert-Prakash reagent, which is versatile for various trifluoromethylation as a trifluoromethyl anion (CF 3 À) equivalent, can be employed as a siladifluoromethyl cation (TMSCF 2 +) equivalent by CÀF bond activation due to the strong interaction between lithium and fluorine atoms. Recently, great attention has been focused on trifluoromethylated compounds in view of their important applications in biological and material science. [1] Synthetic methods for these compounds are generally classified into three types for nucleophilic, electrophilic, and radical trifluoromethylations. In particular, in the nucleophilic case, stable and commercially available trifluoromethyltrimethylsilane (CF 3 TMS; Ruppert-Prakash reagent) [2] as a nucleophilic trifluoromethyl anion (CF 3 À) equivalent has played a key role in the development of trifluoromethylations (Scheme 1, top). [3] On the other hand, synthesis of Supporting information for this article is available on the WWW under

Research paper thumbnail of Formation of 6,8-di-tert-butyl-3,4-dihydro-4,4-dimethyl-1-phosphanaphthalene by the reaction of 2,2-dibromo-1-(2,4,6-tri-tert-butylphenyl)-1-phosphaethene with butyllithium

Chemical Communications, 1997

Sterically crowded 1-bromo-2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyllithium gave 6,8-di-ter... more Sterically crowded 1-bromo-2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyllithium gave 6,8-di-tert-butyl-3,4-dihydro-4,4-dimethyl-1-phosphanaphthalene by intramolecular insertion of an intermediary phosphinidene carbene species into one of the C-H bonds of the two o-tert-butyl groups.

Research paper thumbnail of Combination of sp2‐ and sp3‐Type Phosphorus Atoms for Gold Chemistry: Preparation, Structure, and Catalytic Activity of Gold Complexes That Bear Ligated 2‐Silyl‐1,3‐diphosphapropenes

Chemistry – An Asian Journal, 2011

Kinetically protected 2‐silyl‐1,3‐diphosphapropenes that bear both sp2‐ and sp3‐type phosphorus a... more Kinetically protected 2‐silyl‐1,3‐diphosphapropenes that bear both sp2‐ and sp3‐type phosphorus atoms were employed in the preparation of gold complexes. The structural properties of the 1,3‐diphosphapropene digold(I) complexes were characterized by spectroscopic and crystallographic analyses, which revealed unique aurophilic interactions and conformational properties of the ligand. The 2‐silyl‐1,3‐diphosphapropene‐bis(chlorogold) complexes catalyzed cycloisomerization reactions of 1,6‐enyne derivatives even in the absence of silver co‐catalyst, and were able to be recovered after the reaction. The catalytic activity of the digold complexes primarily depended on the sp2‐type phosphorus atom and the silyl group, and could be tuned by the sp3‐phosphino group. Additionally, results on the catalytic activity of the digold complex in the presence and absence of silver salts showed considerable differences.

Research paper thumbnail of Synthesis, Structure, and Reactivity of Novel 3,4-Diphosphacyclobutenes Bearing Silyl Groups

The Journal of Organic Chemistry, 2005

X-ray crystallography for 5b and 10. A Rigaku RAXIS-IV imaging plate detector with graphite-monoc... more X-ray crystallography for 5b and 10. A Rigaku RAXIS-IV imaging plate detector with graphite-monochromated Mo K α radiation (= 0.71070 Å) was used. The structure was solved by direct methods (SIR92), 1 expanded using Fourier techniques (DIRDIF94), 2 and then refined by full-matrix least squares. Structure solution, refinement, and graphical representation were carried out using the teXsan package. 3

Research paper thumbnail of Modeling the Direct Activation of Dihydrogen by a P2C2 Cyclic Biradical: Formation of a Cyclic Bis(P−H λ5-phosphorane)

Inorganic Chemistry, 2009

The synthesis of a remarkable cyclic bis(P-H lambda(5)-phosphorane) is reported. A stable phospho... more The synthesis of a remarkable cyclic bis(P-H lambda(5)-phosphorane) is reported. A stable phosphorus-heterocyclic biradical, 1,3-diphosphacyclobutane-2,4-diyl, sequentially accepts negatively and positively charged hydrogen atoms to afford 2,4-diphospha-1,3-cyclobutadiene with a diylidic structure containing two P-H bonds.

Research paper thumbnail of Unique molecular distortion in the 2,4,6-tri-t-butylphenyl group

Arkivoc, 2011

X-ray structure of a stable chlorophosphine and a secondary phosphine both bearing one or more st... more X-ray structure of a stable chlorophosphine and a secondary phosphine both bearing one or more sterically bulky 2,4,6-tri-t-butylphenyl (Mes*) group(s) are discussed in terms of molecular distortion. Steric encumbrance of the bulky aromatic ring induces a boat-type structure of the six-membered aromatic ring, and the degree of distortion depends on a substituent in the ipso position.

Research paper thumbnail of Direct α-Siladifluoromethylation of Lithium Enolates with Ruppert-Prakash Reagent via CF Bond Activation

Chemistry - A European Journal, 2014

The direct a-siladifluoromethylation of lithium enolates with the Ruppert-Prakash reagent (CF 3 T... more The direct a-siladifluoromethylation of lithium enolates with the Ruppert-Prakash reagent (CF 3 TMS) is shown to construct the tertiary and quaternary carbon centers. The Ruppert-Prakash reagent, which is versatile for various trifluoromethylation as a trifluoromethyl anion (CF 3 À) equivalent, can be employed as a siladifluoromethyl cation (TMSCF 2 +) equivalent by CÀF bond activation due to the strong interaction between lithium and fluorine atoms. Recently, great attention has been focused on trifluoromethylated compounds in view of their important applications in biological and material science. [1] Synthetic methods for these compounds are generally classified into three types for nucleophilic, electrophilic, and radical trifluoromethylations. In particular, in the nucleophilic case, stable and commercially available trifluoromethyltrimethylsilane (CF 3 TMS; Ruppert-Prakash reagent) [2] as a nucleophilic trifluoromethyl anion (CF 3 À) equivalent has played a key role in the development of trifluoromethylations (Scheme 1, top). [3] On the other hand, synthesis of Supporting information for this article is available on the WWW under

Research paper thumbnail of Formation of 6,8-di-tert-butyl-3,4-dihydro-4,4-dimethyl-1-phosphanaphthalene by the reaction of 2,2-dibromo-1-(2,4,6-tri-tert-butylphenyl)-1-phosphaethene with butyllithium

Chemical Communications, 1997

Sterically crowded 1-bromo-2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyllithium gave 6,8-di-ter... more Sterically crowded 1-bromo-2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyllithium gave 6,8-di-tert-butyl-3,4-dihydro-4,4-dimethyl-1-phosphanaphthalene by intramolecular insertion of an intermediary phosphinidene carbene species into one of the C-H bonds of the two o-tert-butyl groups.

Research paper thumbnail of Combination of sp2‐ and sp3‐Type Phosphorus Atoms for Gold Chemistry: Preparation, Structure, and Catalytic Activity of Gold Complexes That Bear Ligated 2‐Silyl‐1,3‐diphosphapropenes

Chemistry – An Asian Journal, 2011

Kinetically protected 2‐silyl‐1,3‐diphosphapropenes that bear both sp2‐ and sp3‐type phosphorus a... more Kinetically protected 2‐silyl‐1,3‐diphosphapropenes that bear both sp2‐ and sp3‐type phosphorus atoms were employed in the preparation of gold complexes. The structural properties of the 1,3‐diphosphapropene digold(I) complexes were characterized by spectroscopic and crystallographic analyses, which revealed unique aurophilic interactions and conformational properties of the ligand. The 2‐silyl‐1,3‐diphosphapropene‐bis(chlorogold) complexes catalyzed cycloisomerization reactions of 1,6‐enyne derivatives even in the absence of silver co‐catalyst, and were able to be recovered after the reaction. The catalytic activity of the digold complexes primarily depended on the sp2‐type phosphorus atom and the silyl group, and could be tuned by the sp3‐phosphino group. Additionally, results on the catalytic activity of the digold complex in the presence and absence of silver salts showed considerable differences.