Potassium ring opening with

Dehydrogenation of 6-amino-2,3-dihydrobenzo[6]thiophene-l,l-dioxide with stannous chloride dihydrate is reported to afford 6-aminobenzo[6]thiophene-1,1-dioxide.475 It is noteworthy that 2-methyl-2,3-dihydrobenzo[6]thiophene-l,1-dioxide undergoes ring opening with potassium fer -butoxide to give a quantitative yield of 2-propenylbenzenesulfinic acid.279... 

In contrast to the facile ring openings with dimethylsilacyclopropanes, sterically hindered di-r-butylsilacyclopropanes react poorly with alcohols. For example, di-/-butylsilacyclopropane (35) was converted to silane (37) in only 12% yield after refluxing for 20 h in n-butanol. Addition of 10% potassium fluoride and 1% 18-crown-6 to silacyclopropane (35) and n-butanol produced (37) in 79% yield after 15 min at room temperature (Scheme 2). A pentacoordinate siliconate (36) was proposed to account for the rate acceleration <90TL3987>. 

The [Mn(salen)]-catalyzed epoxidation of chromene derivatives was discovered to occur with exceptional enantioselectivity [74]. Chromene derivatives bearing 2,2-disubstitution appear to combine all the important substrate characteristics required for a highly enantioselective epoxidation. The synthetic utility of the enantioenriched epoxychroman products is increased by the predictable regio- and stereochemical outcome of epoxide ring opening with a variety of nucleophiles. These two features were highlighted in the synthesis of the selective potassium channel activator BRL 55834 [78]. Catalyst loadings as low as... 

The diastereoselectivity obtained for reactions on a ring makes it possible to use a cyclic molecule to fix a stereocenter in an acyclic target, as seen in the formation of 154 from 152. Diol 152 had been prepared by a multistep sequence, with control of the stereocenters. When this diol was subjected to oxidation with MCPBA lactone 153 was formed. Subsequent ring opening with methanolic potassium carbonate led to the acyclic fragment 154, with six contiguous stereogenic centers whose stereochemistry had been fixed in the cyclic... 

The next key series of reactions results in the transformation of 625 to 626. The first step is a Sharpless epoxidation of the allylic alcohol. This is followed by a regiospecific oxirane ring opening with potassium benzyloxide to introduce the required oxygen that will eventually... 

The free hydroxy group in 880 is first protected as a benzoate, ring opened with the lithium anion of 1-heptyne, and finally tosylated to afford 881, which is deprotected and cyclized to the epoxide with potassium carbonate in methanol. A Lindlar reduction of the triple bond provides the cw-olefin present in ( —)-(6Z,97 ,10iS)-9,10-epoxyheneicosadec-6-ene (882). In order to prepare the enantiomer 884, 880 is directly ring opened with the lithium anion of 1-heptyne, and then tosylated to afford 883, which is cyclized and selectively reduced to (+ )-(6Z,95, 10/ )-9,10-epoxyheneicosadec-6-ene (884) [250] (Scheme 192). 

Y = F) with sodiiun methoxide, but undergoes ring-opening with potassium hydroxide in t-butyl alcohol to give the acid o-C F4H-CF CF-C02H, whidi is converted into the dichloro-compound o-CsFaH-CFCl-CFCl-COaH by treatmmt with phosphorus pentachloride followed by hydrolysis. Both 3-chloroh tafluoro-and octafluoro-indene are converted into the oxo-sulphonic add (32) by 20% oleum, and the dibromide (33a) or the nitro-indane (33b) is formed when octa-fluoioindene reacts with bromine or HNOa-HF, respectively. The fomiation of the antiaromatic cabocation (34) when octafluoroindene dissolves in SbFs-SOa at -40°C has been briefly studied by n.m.r. spectroscopy. ... 

Potassium hydroxide 3,4-Dihydroisoquinolinium ring opening with and without naphthalene ring closure... 

Potassium tert-butoxide Z 2-Thiazoline ring opening with subsequent transesterification of thioiminoesters... 

Potassium hydroxide Cyclopropanol ring opening with and without skeletal rearrangement 663. OH... 

From Multiring Systems Containing Pyrazoles. The pyrazolopyrimidine (65) on treatment with diazomethane forms the cyclopropane (66), which undergoes a ring-opening reaction with potassium hydroxide to yield the pyrazole (67) (eq. 16) (44). 

Potassium t-butoxide in t-butyl alcohol requires powerful electron-attracting substituents at C-4 to effect ring opening of pyrazoles but sodamide does not (Scheme 26) (B-76MI40402). As the key to the transformation is the generation of the anion, similar results were obtained by heating some pyrazole-3-carboxylic acids with quinoline. 

Pyrazoles can be prepared by ring opening reactions of fused systems already containing the pyrazole nucleus. Thus several [5.5], [5.6] and [5.7] fused heterocycles have been opened to substituted pyrazoles, usually in basic medium. In general, the method has little preparative interest since another pyrazole derivative has usually been used to build the ring-fused system. However, due to the unexpected structures obtained, two publications are worthy of notice. 6//-Cyclopropa[5a,6a]pyrazolo[l,5-a]pyrimidine (638) was readily obtained from the corresponding pyrazolopyrimidine by the action of diazomethane at room temperature (Scheme 59) (81H(15)265). When (638) was treated with potassium hydroxide, the pyrazole (640) was formed, probably via the diazepine (639). 

The oxaziridine ring itself is stable towards alkali there is, for instance, no substitutive ring opening by hydroxyl ions as in oxiranes. 2-r-Butyl-3-phenyloxaziridine (56) is not attacked by methoxide ion in methanol during 12 h at room temperature 3-isopropyl-2-r-octyloxaziridine does not react at room temperature with either solid potassium hydroxide or potassium methoxide solution (57JA5739). 

A decisive solvent effect is also observed with other a,/ -epoxy ketones. Specifically, 3jS-hydroxy-16a,17a-epoxypregn-5-en-20-one and its acetate do not react with thiocyanic acid in ether or chloroform. However, the corresponding thiocyanatohydrins are formed by heating an acetic acid solution of the epoxide and potassium thiocyanate. As expected, the ring opening reaction is subject to steric hindrance. For example, 3j6-acetoxy-14f ,15f5-epoxy-5) -card-20(22)-enoIide is inert to thiocyanic acid in chloroform, whereas the 14a,15a-epoxide reacts readily under these conditions.Reactions of 14a,15a-epoxides in the cardenolide series yields isothiocyanatohydrins, e.g., (135), in addition to the normal thiocyanatohydrin, e.g., (134). 

Rearrangement of fluorine with concomitant ring opening takes place in fluorinated epoxides Hexafluoroacetone can be prepared easily from perfluo-ropropylene oxide by isomerization with a fluorinated catalyst like alumina pre treated with hydrogen fluoride [26, 27, 28] In ring-opening reactions of epoxides, the distribution of products, ketone versus acyl fluoride, depends on the catalyst [29] (equation 7) When cesium, potassium, or silver fluoride are used as catalysts, dimenc products also are formed [29]... 

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