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It could be shown that the more negatively charged the substituent R in 131 is, the longer and thus weaker the C3–C4 bond becomes, which nicely parallels the observed rate accelerations (Scheme 42). Max J. Gough, John Steele, in Comprehensive Organic Functional Group Transformations, 1995. No structural data have been reported, but it has been used in the synthesis of the volatile Nd(C5H4CH2CHMe2)2. Potassium hydroxide react with carbon dioxide. Cohen and coworkers found that exposure of the diastereomeric 2-(2-furyl)cyclobutanols (169; Scheme 18) to potassium hydride in THF at room temperature results in rearrangement to the tetrahydrobenzofuran (171), albeit in modest yield.65a However, under the same conditions the tertiary alcohol (170) suffers fragmentation to ketone (172), presumably via heterolytic cleavage of the alkoxide followed by proton transfer. We use cookies to help provide and enhance our service and tailor content and ads. Extended structure of [K(THF)2Sm(C5Me5)2OC6H2tBu2-2,6-Me-4], 44. Installing oxygen or sulfur moieties at the terminal carbon atom of the bridgehead vinyl group in 132 accelerated the Cope rearrangement toward 133 by 1.4- and 3.45-fold, respectively (Scheme 43).52 During the assembly of the diterpenoid vinigrol, an additional unsaturation significantly accelerated the sigmatropic process. 27. To differentiate between Gram negative and Gram positive organisms. Like the Gram stain reaction, the KOH test is based on differences in the chemistry of the bacterial cell wall. N-Alkylation can be achieved with alkyl halides in acetone in the presence of K2CO3 or in dimethylformamide with sodium ethanolate 〈87JCS(P1)2163, 93H(36)1027〉. Cohen has suggested that the chelated species (179) may be involved as an intermediate leading to the endo-alcohol in the case of the reaction carried out in THF alone. It should be noted, however, that these generalizations only appear to be applicable to reactions carried out in highly dissociating media. Although 134 required heating under reflux in THF for over 22 h to give rise to 135, the additional unsaturation in 136 greatly facilitated the process and led to a quantitative rearrangement to furnish 137 within just 2 h at room temperature.53, E. Butkus, in Comprehensive Organic Synthesis II (Second Edition), 2014, Treatment of 3,3,8-tribromocamphor 248 with potassium anilide (generated in situ from potassium hydride and aniline) in THF at room temperature for 7 h lead to an interesting tricyclic compound 250 in 85%. To a suspension of 3.44 g potassium hydride (24% content, dispersed in mineral oil) in 50 mL dry THF at − 10° under an atmosphere of N2 was added 0.92 g (7.39 mmol) methyl methylsulfinylmethyl sulfide. 25. An X-ray structure determination showed that this contained a “tripledecker cation” [([18]-crown-6)Na([18]-crown-6)Na([18]-crown-6)]2 + and two [CsHPh4]– anions. On the other hand, the intramolecular addition of unactivated alkenes to ketenes is a more efficient process, and Snider and coworkers have recently employed this strategy to prepare the tetracyclic vinylcyclobutanone derivative (202; Scheme 24).71 Reduction of this ketone with sodium borohydride furnished the cyclobutanols (203) as a 19:1 mixture of diastereomers, which were then converted to the corresponding potassium salts in the usual fashion by treatment with excess potassium hydride. It is also used as a reducing agent to reduce hindered boranes and borates to substituted borohydrides. In contrast to (74), compounds (75) are easily hydrolyzed to amidoximes. A solution of the 1,3-bis(1-adamantyl)imidazol-2-ylidene in THF-d8, sealed under a few atmospheres of CO, has shown no decomposition or change after 7 years at room temperature<2002UP001>. The reaction of α,α-dihalogeno bicyclo[3.3.1]nonanediones 262 under Favorskii raction conditions in the presence of sodium methoxide, ethoxide, propoxide, and potassium cyanide led to the intramolecular ring closure via C–O bond formation giving the highly functionalized chiral 2-oxatricyclo[,8]decanes (2-oxaprotoadamantane) 264. The formation of 261 can be rationalized mechanistically through an intramolecular nucleophilic ring opening of the bromocyclopropanone intermediate 260 by the keto ester enolate anion. These stereochemical results were interpreted as being consistent with a concerted mechanism, in which the exo isomer (160) rearranges via a suprafacial inversion (si) pathway as in the thermal 1,3-sigmatropic shifts (equation 26) studied earlier by Berson. Principle. The attraction between the positive and negative ions keeps them in place. The mother liquor was concentrated and purified by column chromatography (silica gel; EtOAc/hexane 1:1) followed by recrystallization from EtOH to give additional 0.5 g of 10; m.p. Although these results are in accord with the stereochemical predictions for concerted 1,3-sigma-tropic rearrangements, it is likely that in most if not all cases the accelerated VCB rearrangement follows a stepwise pathway involving allylmetal aldehyde intermediates. The transformations summarized in Scheme 20 provide further insight into the stereochemical course of the oxyanion-accelerated VCB rearrangement. Potassium hydride, whose formula is represented as KH, is an inorganic substance that is classified as an alkali metal hydride because it is formed by directly combining molecular hydrogen with potassium through the following reaction: H 2 + 2K → 2KH This reaction was discovered by the same scientist who identified potassium for the first time. However, an alternative SN2′ reaction of the bromo enolate anion cannot be ruled out (Scheme 80). The formation of the bromocyclopropanone 260 appeared to be the result of a preferential loss of equatorial bromide as opposed to the loss of an axial bromide (position 6 in 259). Likewise, alkylation of the silver salts of (74) affords mixtures of O- and N-alkyl products 〈64HCA838〉 while the sodium salt furnishes the thermodynamically preferred N-alkyl compound with ethyl chloroacetate 〈84CB2999〉. Fig. Intramolecular nucleophilic ring opening at C-6 followed by protonation provides 256, whereas nucleophilic attack at C-8 followed by an intramolecular aldol-addition to the keto group leads to the tetracyclic ketol 257 (Scheme 81).106, The dehydrobromination of similar dibromo ester 259 with either DBU in THF or with LiBr/Li2CO3 in DMF gave tetracyclic 261 as the sole product in 70% isolated yield. The mean K–C distance was 315.9 pm and the c–K–c angle was 137.9° with the THF coordinated on the open side of the central potassium atom. Although the endo-bicycloheptenol (163) was stable under these conditions, 1,3-rearrangement did occur upon heating or in the presence of added 18-crown-6. Exposure of this mixture of vinylcyclobutanols to excess potassium hydride in THF at reflux next induced 1,3-rearrangement to afford (193), which without purification was oxidized and isomerized to the conjugated enone (194) in 65% overall yield. It should be noted, however, that the scope of this reaction is limited to the more ketenophilic alkenes; simple alkenes such as 1-hexene react slowly with vinylketenes at 90 C to produce the desired 2-vinylcyclobutanones in relatively low yield. Discovered in 1975 by Evans and coworkers, the AOC of 128 using potassium hydride (KH) as base to generate the corresponding potassium alkoxide resulted in observed rate accelerations of 1010–1017 to afford the rearranged enolate 129, which was then protonated to ketone 130 (Scheme 41).50 The reaction rate displayed strong counter ion dependence, and the potassium alkoxide proved to be the optimal substrate, especially when crown ether such as 18-crown-6 was added, which resulted in additional 180-fold rate acceleration.

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