1912-61-4Relevant academic research and scientific papers
Efficient chemoselective mild deprotection of S,S-and S,O-acetals and ketals with electrophilic halogens
Shaterian, Hamid Reza,Hadadzadeh, Hassan
, p. 1059 - 1071 (2007/10/03)
A novel and simple method for the chemoselective deprotection of S,S- and S,O-acetals and ketals in the presence of their O,O-analogs with electrophilic halogens to their corresponding carbonyl compounds is described using N-bromosuccinimide, N-chlorosuccinimide, 2,4,4,6-tetrabromo-2,5-cyclohexen-1- one, trichlorocyanuric acid, or molecular bromine in aqueous acetonitrile. The use of these reagents in the presence of hydrated silica gel provide efficient, novel, and mild procedures for the deprotection of cyclic and acyclic O,O-, S,S-, and S,O-acetals and ketals in excellent yields in short reaction times. Copyright Taylor & Francis Group, LLC.
A simple and efficient radical reduction using water-soluble radical initiator and hypophosphorous acid in aqueous alcohol
Nambu, Hisanori,Alinejad, Anahita Hessamian,Hata, Kayoko,Fujioka, Hiromichi,Kita, Yasuyuki
, p. 8927 - 8929 (2007/10/03)
A simple, mild and high-yielding procedure for the reduction of various halogenated compounds using a combination of the water-soluble radical initiater (VA-061), hypophosphorous acid and triethylamine in aqueous alcohol is reported. A simple, mild, and high-yielding procedure for the reduction of various halogenated compounds using a combination of the water-soluble radical initiator, 2,2′-azobis[2-(2-imidazolin-2-yl)propane] (VA-061), a water-soluble chain carrier, hypophosphorous acid, and the base, triethylamine, in aqueous alcohol is described. The reagents used in this method are all water soluble, and therefore, an almost pure desired product can be readily obtained using only an extraction procedure.
Barium Permanganate, Ba(MnO4)2, a versatile and mild oxidizing agent for use under aprotic and non-aqueous conditions
Firouzabadi,Seddighi,Mottaghineiad,Bolourchian
, p. 6869 - 6878 (2007/10/02)
Barium Permanganate is an easily prepared, stable, and a versatile oxidation reagent. With this reagent different types of primary and secondary hydroxy compounds are converted to their carbonyl derivatives. Aldehydes could be transformed to their carboxylic acids. Benzylic chloride and bromides are converted to their aldehydes and carboxylic acids. Semicarbazide and 2,4-dinitrophenylhydrazine derivatives of benzylic carbonyl compounds undergo carbon-nitrogen bond cleavage selectively and yield the expected carbonyl compounds. p-Hydroquinone is converted to p-benzoguinone and aromatic amines to their azo compounds. Anthracene and phenanthrene produce their 9,10-quinones. Diphenyl acetylene and trans stilbene give benzil, and styrene produces benzaldehyde. Selective oxidations of secondary benzylic carbon-hydrogen bonds occur and the corres- ponding carbonyl compounds are produced in good yields.
Formation of vinyl halides from vinyl cations generated by acetylenic participation in biomimetic polyene cyclizations
Johnson, William S.,Ward, Carl E.,Boots, Sharon G.,Gravestock, Michael B.,Markezich, Ronald L.,McCarry, Brian E.,Okorie, Dominic A.,Parry, Ronald J.
, p. 88 - 98 (2007/10/02)
The object of this study was to examine the fate of vinyl cations of type 4 (resulting from biomimetic polyene cyclizations) in the presence of various halides as sources of nucleophiles. Treatment of the dienynol 1 with trifluoroacetic acid in methylene chloride for 45 min at -78°C resulted in the isolation of the rearranged bicyclic vinyl chloride 6 in 56% yield. Confirmation of the structure and isomeric purity of 6 was obtained by exhaustive ozonization to give diketo ester 9 followed by Wolff-Kischner reduction and then esterification to yield ester 10, the structure of which was confirmed by hydrogen-deuterium exchange of the protons α to the carbomethoxy group. The configuration of the ring fusion in 6 was shown to be trans in the following manner. Selective ozonization gave chloro ketone 11, which was converted into chloro olefin 12 by Wolff-Kischner reduction. Further ozonization afforded keto ester 13, which was converted into diacid 15 by sodium hypobromite oxidation. Esterification afforded diester 16, which was identical with the material obtained via Wolff-Kischner reduction of the known keto diester 17. More careful examination of the products from the aforementioned cyclization also showed the presence of 8% ketone 8 (after hydrolytic workup). Identical cyclization conditions of 1, except at 0°C, gave 55% vinyl chloride 6 and 45% ketone 8 while use of a 7.5:1 pentane-1,2-dichloroethane mixture at 0°C led to 11% vinyl chloride 6 and 89% ketone 8. Cyclization of dienynol 1 with stannic chloride in 1,1-dichloroethylene at -35°C for 45 min gave a 53% yield of three isomeric vinyl chlorides, 7b, 7a, and 6, in a ratio of 8:75:12. The successful cyclization of dienynol 1 led to more extensive cyclization studies of substrates such as 2, 3, and 35, which provided tetracyclic products. The most thoroughly studied case was that of trienynol 3, which, on treatment with stannic chloride in 1,1-dichloroethylene at ca. -30°C for 50 min, gave a 64% yield of three tetracyclic products A, B, and C in a ratio of 15:73:12 by VPC. Product A was shown to be chloro diene 22 by hydrogenation of the Δ1-olefinic bond followed by ozonization to give 5β,13α-androstan-17-one (29), which was compared with an authentic sample prepared by irradiation of 5β-androstan-17-one (25). Products B and C were shown to be chloro dienes 18 and 20 by conversion of the mixture into 5β-androstan-17-one (25) and keto ester 27. A systematic variation of reaction conditions as well as the use of mixed-halide sources led to evidence for a possible mechanism for the formation of all three products from an intermediary tricyclic cation 43.
