Olefins alcohol addition

Depending on the electronic state of azafulvalene and the reaction conditions, simple nucleophiles such as amines or alcohols show a different behavior. Upon heating methanol reacted with azafulvalenes as electron-rich olefins by addition to the central double bond (64BSF2857 67LA155). Using the TAF 77 (Ar = Ph), the addition reaction in a neutral benzene-ethanol solution required several days to obtain a minor amount of 147, while the reaction proceeded rapidly in the presence of a catalytic amount of potassium hydroxide (79JOC1241). Tlie yellow-colored adduct 147 can be reconverted to the quinoid starting material by irradiation (Scheme 58). 

Since electron-donating substituents at the phosphorus atom favor addition reactions over olefination reactions, addition of 9 to aldehydes leads to the exclusive formation of the silyl-pro-tected allylic alcohols 10. No reaction products arising from Wittig alkenylation could be detected. The ylides (R,S)-9 and (S.S)-9 and their enantiomers were prepared from the corresponding optically pure l-[2-(diphenylphosphino)ferrocenyl]-A,A -dimethylethanamine diastereomers 7 via the phosphonium salts 8. 

Ionizing radiations (a, ft and y) react unselectively with all molecules and hence in the case of solutions they react mainly with the solvent. The changes induced in the solute due to radiolysis are consequences of the reactions of the solute with the intermediates formed by the radiolysis of the solvent. Radiolysis of water leads to formation of stable molecules H2 and H2O2, which mostly do not take part in further reactions, and to very reactive radicals the hydrated electron eaq, hydrogen atom H" and the hydroxyl radical OH" (equation 2). The first two radicals are reductants while the third one is an oxidant. However there are some reactions in which H atom reacts similarly to OH radical rather than to eaq, as e.g. abstraction of an hydrogen atom from alcohols, addition to a benzene ring or to an olefinic double bond, etc. 

From A17(20)-Olefins The addition of an oxygen function to C-20 is best accomplished by the hydroboration-oxidation reaction on a A17(20) olefin. The ready preparation of such olefins has been discussed earlier predominantly m-olefins are obtained via the Wittig reaction on 17-keto steroids, and the /ra/w-olefins via dehydration reactions. Hydroboration-oxidation of m-A17(20)-olefins gives the 20a-alcohol in high yield, presumably by attack of diborane on the a-side of the double bond 137... 

Diphenyl diselenide is an especially useful co-reagent with [bis(acetoxy)-iodo]benzene. For example, the BAIB/PhSeSePh (2 1) combination has been employed for trans, Markovnikov additions of PhSeOAc and PhSeOH to alkenes [35]. Such formal additions appear to be regulated by seleniranium intermediates, and were extended to intramolecular cyclizations of olefinic alcohols, carboxylic acids, and / -dicarbonyl compounds (Scheme 12). 

For the first example, we chose to acylate olefin alcohol la. This was readily accomplished using acetic anhydride and 4-DMAP in pyridine to provide ester 17. Methylenation, using Takai s (10) protocol, yielded the acyclic enol ether 18 which was subsequently cyclized with 15 mol % of the Schrock catalyst 6 in hot toluene to afford the glycal 19 in good yield. Hydroboration and oxidative work-up led to the methyl-C-glycoside 20 (Scheme 4). With this proof of principle in hand, we then set out to prepare a number of additional examples as shown in Table 1 (11). 

A number of additional examples were studied. The carbohydrate-based carboxylic acids, the olefin alcohols and the protecting groups were all varied (Table 2) (14). 

An indirect PET methodology known as redox photosensitization has been developed by Pac [45] and Tazuke [64] for achieving higher yields of nucleophile addition product to alkene cation radicals. One recent example of this approach may be mentioned by illustrating anti-Markonikov alcohol addition (e.g. 61-62) to non conjugated olefin 61 using biphenyl as cosensitizer [65]. More examples on this topic can be found in Farid [5] and Mariano s [11] reviews. 

In a similar manner, Grignard reagents react with cyclic a,/3-dihalo ethers derived from 3,4-dihydro-l,2-pyran and tetrahydrofuran to form the corresponding 2-alkyl-3-halo derivatives. Thus, addition of 2,3 dibromotetrahydropyran to methylmagnesium halide at 0° followed by hydrolysis gives a 65% yield of 2-methyl-3-bromotetrahydropyran. These materials are valuable intermediates in the synthesis of olefinic alcohols (cf. method 99). 

Alcohols, addition—Continued to olefinic compounds, 232 to oxides, 233... 

Olefinic acetals, preparation, 263 preparations listed in table 23, 268 a, S-01efinic acetals, preparation, 37 Olefinic acetylenes, addition of alcohols, 233, 266 alkylation, SO partial reduction, 46 preparatioh, 34, 39, 46, 48, 80 preparations listed in table 6, 84 Olefinic acids, addition, of halogen, 107... 

A conjugated double bond system undergoes 1,4-addition (Thiele s rule) for example, butadiene and an equimolar quantity of bromine yield 1,4-dibromo-2-butene (90%). On the other hand, chlorination of butadiene in the liquid or vapor phase furnishes about equal amounts of 1,2-and 1,4-addition products. Other polyfunctional compounds resulting from this method of preparation include dihalogenated acids, esters, aldehydes, and ketones. < The addition of bromine to unsaturated ethers yields dibromo ethers which are used as intermediates in the synthesis of olefins (method 21) and olefinic alcohols (method 99) ... 

Olefinic alcohols are best prepared by the action of lithium aluminum hydride on the corresponding acid or ester as in the preparation of 3-penten-l-ol (75%). The double bond may be in the a,/S-position to the ester group, The Bouveault-Blanc procedure has also been used with success for reduction of nonconjugated olefinic esters. The addition of the sodium to an alcoholic solution of the ester is superior to the reverse addition of. the ester to sodium in toluene for the preparation of 2,2-dimethyl-3-buten-l-ol (62%). Selective catalytic hydrogenation is inferior. Large amounts of catalyst are required, and the products contain saturated alcohols. ... 

Copper(I) and (II) Lewis acids affect the alkoxyselenation of olefins (Sch. 18). Thus, cyclohexene affords trans adducts 71 in the presence of PhSeCN and CUCI2 [44]. The Lewis acid enhances the electrophilic nature of the selenium by coordination to the nitrile. The reaction is regioselective as terminal olefins afford primary selenides (alcohol addition to the internal carbon) and vinyl acetates yield (8-seleno-a-alkoxyacetates. 

The rate of imine disappearance increased from MeOH (relative rate 1.0) to EtOH (2.0), PrOH (2.0) and fPrOH (3.3), in agreement with the easier oxidation of these alcohols. BuOH does not follow this correlation since it induces a relative rate of only 1.8, giving rise to the formation of more side products. In the case of iPrOH, involvement of the intermediate hydroxyalkyl radical was corroborated through detection of its disproportion product acetone. These results show that the solvent can be directly involved in the oxidative step. Formation of hydrodimers in the absence of olefins thus can be explained by the oxidation of the alcohols. It is noted that in the presence of olefins no alcohol addition products could be detected by HPLC analysis, although methanol is present in a 500-fold molar excess. 

Hydration and Dehydration Reactions. Hydration and dehydration catalysts have a strong affinity for water. One such catalyst is AI2O3, which is used in the dehydration of alcohols to form olefins. In addition to aliunina, silica-alumina gels, clays, phosphoric acid, and phosphoric acid salts on inert carriers have also been used for hydration-dehydration reactions. An example of cm industrial catalytic hydration reaction is the synthesis of ethanol from ethylene ... 

Compared with primary alcohols, secondary alcohols underwent competitive dehydration to yield olefins in addition to O-benzylation products in the presence of KY. 

Ring scission of cyclic p-halogeno ethers to olefinic alcohols mediated by Sml2 has been studied. Scission in the tetrahydrofuran series could be accelerated by addition of HMPA or DMPU with only a small deterioration in diastereo-selectivity, but in the tetrahydropyran series there was a drastic change in the stereochemistry of the product when DMPU was used. Obviously, DMPU has a substantial effect on the formation and conformation of complexes in solution [88,89]. 

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