- Complexation of dichlorocarbene by methylanisoles
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Dichlorocarbene generated by laser flash photolysis of dichlorodiazirine readily forms UV-vis active π- and O-ylidic complexes with methylanisole derivatives.
- Moss, Robert A.,Wang, Lei,Odorisio, Christina M.,Krogh-Jespersen, Karsten
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Read Online
- Syntheses of extreme sterically hindered 4-methoxyboronic acids
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4-Iodoanisoles 3a,b, 3d and 4-bromoanisoles 4a-d were readily obtained. An extreme steric hindrance precluded obtaining 3c. Catalytic borylation of 3a,b, 3d followed by hydrolysis of boronic ester 26a,b, 26d easily provided the boronic acids 5a,b, 5d. Com
- Diemer, Vincent,Chaumeil, Hélène,Defoin, Albert,Carré, Christiane
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experimental part
p. 918 - 929
(2010/03/25)
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- Trifluoroacetic Acid-catalysed Transacylation of Arenes by Acylpentamethylbenzene
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Facile transacylation between acylpentamethylbenzene and activated arenes such as anisole was found to occur in boiling trifluoroacetic acid (TFA).The mechanism for the transacylation between acetylpentamethylbenzene (AcPMB) and anisole with TFA was elucidated by means of product isolation and kinetics.The reaction proceeds via reversible protodeacetylation of AcPMB involving an ipso-protonated intermediate B to give pentamethylbenzene and acetic trifluoroacetic anhydride followed by irreversible acetylation of anisole by the mixed anhydride.The mechanism resulting in an ipso-protonated intermediate B was deduced from the reaction of acetylmesitylene with TFA as well as from the rate of deacetylation of 3,5-dideuterioacetylmesitylene with TFA.The formation of such an intermediate was also independently confirmed by 13C n.m.r. spectroscopic syudies on AcPMB in superacid solutions under stable conditions.
- Keumi, Takashi,Morita, Toshio,Shimada, Takanobu,Teshima, Naomi,Kitajima, Hidehiko,Prakash, G. K. Surya
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p. 847 - 852
(2007/10/02)
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- Method for protecting guanidino group and restoring the same
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A guanidino group in an amino acid or a peptide can be protected with a specific group, i.e. pentamethylbenzensulfonyl, 2,4,6-trimethoxybenzenesulfonyl, 4-methoxy-2,3,5,6-tetramethylbenzenesulfonyl, 4-methoxy-2,6-dimethylbenzenesulfonyl or 4-methoxy-2,3,6-trimethylbenzenesulfonyl, and said group may easily be removed without affecting the amino acid or the peptide to be derived from the protected amino acid or peptide. Thus, the present invention is useful in the synthesis of peptides containing the guanidino group.
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- Synthesis of Substituted Dibenzophospholes. Part 2. Syntheses of Intermediate Biphenyls and Quaterphenyls
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A general procedure for synthesis of 4",6'-dialkoxy-2',2"-diamino-m-quaterphenyls has been established.Copper(I) t-butoxide is used to prepare 2,6-dinitrophenyls from 1,3-dinitrobenzene and aryl iodides.One of the nitro-groups is then exchanged for a methoxy-group by sodium methoxide in hexamethylohosphoramide; the resulting 2-methoxy-6-nitrobiphenyls are then iodinated in the 5-position.Ullmann coupling then gives the dinitroquaterphenyls which are reduced to the diamines.An alternative route from 2,2',4,4'-tetranitrobiphenyl was explored; arylation was easy but alkoxydenitration was indiscriminate.Some 71 new derivatives of biphenyl, terphenyl, and quterphenyl are reported.
- Cornforth, John,Sierakowski, Andrew F.,Wallace Timothy W.
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p. 2299 - 2316
(2007/10/02)
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- Further Studies on the Use of Multi-substituted Benzenesulfonyl Groups for Protection of the Guanidino Function of Arginine
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Various multi-substituted benzenesulfonyl protecting groups for the guanidino function of arginine, removable under mild conditions such as with trifluoroacetic acid (TFA)-thioanisole, were studied.Among them, the 4-methoxy-2,6-dimethylbenzenesulfonyl (Mds) group, the 2,3,4,5,6-pentamethylbenzenesulfonyl (Pme) group, and the 4-methoxy-2,3,6-trimethylbenzenesulfonyl (Mtr) group were found to be useful.Both Mds and Pme show considerable resistance to TFA and, therefore, are suitable for procedures in which the intermediates are deprotected by TFA treatment, while Mtr is the most useful protecting group when TFA treatment is not necessary.Keywords---4-methoxy-2,6-dimethylbenzenesulfonyl (Mds); 2,4,6-trimethoxybenzenesulfonyl (Mtb); 2,3,4,5,6-pentamethylbenzenesulfonyl (Pme); 4-methoxy-2,3,6-trimethylbenzenesulfonyl (Mtr); trifluoroacetic acid-thioanisole deprotection
- Fujino, Masahiko,Wakimasu, Mitsuhiro,Kitada, Chieko
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p. 2825 - 2831
(2007/10/02)
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