Subject vinyl substitutions

Several epoxides hearing multiply-bonded substituents have Wu subjected to alcohol addition. Treatment of several vinyl-substituted ethylene oxides with sodium metboxide, for example, has been reported to yield alcohols corresponding to attack on the epoxide carbon iLtnnt furthest from the uiwaturated function. 6-l8S8- . > In the presence of a trace of mineral acid, however, methanol adds to the opposite terminal of the epoxide ring (Eq. 666),... 

Vinyl substitutions on alkenes not having their double bonds conjugated with carbonyl groups often proceed more rapidly and give better product yields when the reactions are conducted in the presence of an unhindered secondary amine. Conjugated and nonconjugated dienes are usually only minor products in these cases. The major products normally are allylic amines obtained by nucleophilic attack of the secondary amine upon the ir-allylpalladium intermediates. Since allylic amines may be quatemized and subjected to the Hoffmann elimination, this is a two-step alternative to the direct vinyl substitution reaction.90... 

The base-catalysed cis-trans isomerization of l-aryl-2-phenylcyclopropanes has been subjected to kinetic analysis and a complexed anion, e.g. (190), is thought to be produced initially. Configurational inversion of the cyclopropyl sulphoxide (173) can also be effected by base. A kinetic analysis of the hydrolysis of 2- and 2,2-di-substituted bromocyclopropanes suggests that for 2-vinyl-substituted compounds considerable progress towards an allyl cation has been been made at the transition state. Metallation studies show that, for nortricyclanes at least, the cyclopropyl hydrogen atoms are most readily attacked by pentylsodium in the presence of potas-... 

The nuclear substituted methyl styrenes have been the subject of much study and of these poly(vinyl toluene) (i.e. polymers of m- and /7-methylstyrenes) has found use in surface coatings. The Vicat softening point of some nuclear substituted methyl styrenes in given in Table 16.8. 

The possibility of incorporating unsaturated groups into the polymers, as potential sites for crosslinking, is also being explored. For example, the vinyl (7, 8), ally (9), and butenyl (10) substituted phosphoranimines have been prepared and subjected to the usual thermolysis and cothermolysis conditions (eq 3). In these cases, all of which have a terminal... 

Palladium-catalyzed bis-silylation of methyl vinyl ketone proceeds in a 1,4-fashion, leading to the formation of a silyl enol ether (Equation (47)).121 1,4-Bis-silylation of a wide variety of enones bearing /3-substituents has become possible by the use of unsymmetrical disilanes, such as 1,1-dichloro-l-phenyltrimethyldisilane and 1,1,1-trichloro-trimethyldisilane (Scheme 28).129 The trimethylsilyl enol ethers obtained by the 1,4-bis-silylation are treated with methyllithium, generating lithium enolates, which in turn are reacted with electrophiles. The a-substituted-/3-silyl ketones, thus obtained, are subjected to Tamao oxidation conditions, leading to the formation of /3-hydroxy ketones. This 1,4-bis-silylation reaction has been extended to the asymmetric synthesis of optically active /3-hydroxy ketones (Scheme 29).130 The key to the success of the asymmetric bis-silylation is to use BINAP as the chiral ligand on palladium. Enantiomeric excesses ranging from 74% to 92% have been attained in the 1,4-bis-silylation. 

The 1,3-diene moiety in 227 which included the carbon atoms and CVC was oxidized to the l,4-dihydroxy-2-ene moiety in 238 that was further exploited to functionalise the A-ring as well as for the annulation of the C-ring (Scheme 37). The transformation of 227 into 238 was realized by a diastereoselective epoxidation of 227 to afford a vinyl epoxide (241) that was subjected to the conditions for a Palladium(O)-catalysed allylic substitution with the acetate ion [126]. The mechanism and the stereochemical course of the allylic substitution may be explained as depicted in Scheme 37. Sn2 ring opening of the protonated vinyl epoxide 241 by an anionic Pd complex proceeded with a (3Si) topicity to the r-allyl Pd com-... 

A beautiful extension of this reaction has recently been communicated by Nozaki, Oshima, and Utimo-to.184 These workers simply admixed f-butyl iodide (3 equiv.), benzaldehyde (1 equiv.), methyl vinyl ketone (1 equiv.) and triethylborane (1 equiv.) in benzene (Scheme 60). After 5 min at 25 C, the reaction was subjected to standard extractive work-up and the crude product was purified by chromatography to give (54) in 63% yield. If methanol is substituted for benzaldehyde, the protonated product (55) is isolated in 79% yield. Although enones are equivalents of synthon (56), such a direct coupling of radical and ionic reactions had not been achieved previously. 

One of the best known reactions of 1-azirines is the acid/catalyzed hydrolysis to aminoketones. Since the Neber reaction also accomplishes this same synthetic end, this reaction may appear to have little practical value. This is not the situation because with the Neber reaction there is no control over the aminoketone that will be obtained from a given ketone. For example, when oxime (127) derived from benzyl methyl ketone (126) is subjected to the Neber reaction aminoketone 128 is obtained.59 The amino function is substituted for the most acidic a-hydrogen. The isomeric aminoketone (132) that could not be prepared by the Neber reaction can be formed by the hydrolysis of 1-azirine (131). The synthesis of this 1-azirine has been accomplished from allyl benzene (129) through vinyl azide (130) using iodine azide.22... 

Heteroaromatic-substituted vinyl compounds were successfully subjected to the AA reaction, too. In contrast to styrene substrates, 2-vinylfuran was convert-... 

Equally, a 1.5 1 mixture of cis- and frans- 1,3-dibromo propene reacts with sodium dimethyl methylmalonate to furnish the vinyl bromo derivative 79 in excellent yield, which in turn is transformed in a one-pot fashion to a 1.5 1 mixture of enyne 80 or the corresponding Suzuki products 81 and 82 (Scheme 24). Interestingly, (( )-3-bromo-propenyl)-tributylstannane furnishes the vinyl stannane 83 upon allylic substitution that instantaneously is subjected to the conditions of a Stille coupling with iodo benzene to give the sequence s product 84 in 68% yield (Scheme 25). 

The boroxines could then be subjected to Suzuki coupling with aryl, vinyl, or benzyl halides. Suzuki coupling with tri- -butylstannyl chloride also gave the tri- -butylstannyl-substituted thiophenes 221. These can form the starting materials for further transformations. The carbonylative coupling with halides resulted in the formation of ketones tin-lithium exchange followed by reaction with electrophiles led to a host of other useful products (Scheme 65). 

Since the disclosures that the thermal dimerizations of acrolein and methyl vinyl ketone provide the 3,4-dihydro-2//-pyrans (1, 2) derived from 4ir and 2Tt participation of the a,3-unsaturated carbonyl compound in a Diels-Alder reaction, an extensive series of related observations have been detailed. This work has been the subject of several comprehensive reviews - - including the Desimoni and Tacco-ni extensive tabular compilation of work through 1974. Consequently, the prior reviews should be consulted for thorough treatments of the mechanism, scope, and applications of the [4 + 2] cycloaddition reactions of a,3-unsaturated carbonyl compounds. The [4 + 2] cycloaddition reactions of 1-oxa-1,3-butadienes with their 4-it participation in the Diels-Alder reaction exhibit predictable regioselectivity with the preferential or exclusive formation of 2-substituted 3,4-dihydro-2W-pyrans (equation 1). The exceptions to the predicted regioselectivity that have been observed involve the poorly matched [4 + 2] cycloaddition reaction of an electron-deficient l-oxa-l,3-butadiene with an electron-deficient dienophile, e.g. methyl crotonate or methacrolein. - Rigorous or simplified theoretical treatments of the [4 + 2] cycloaddition reaction of 1-oxa-1,3-butadienes predict the preferential formation of 2-substituted 3,4-dihy-dro-2f/-pyrans and accommodate the preferred endo approach of the reactants in which the carbon-carbon bond formation is more advanced than carbon-oxygen bond formation, i.e. a concerted but nonsynchronous [4 + 2] cycloaddition reaction. ... 

Danishefsky and co-workers exploited a 6-exo intramolecular vinylic Heck substitution reaction en route to a total synthesis of ( )-FR-900482 (76) (Scheme 6-12) [26]. The efficient conversion of aryl iodide 70 to tetracycle 71 is illustrative of the impressive functional-group tolerance displayed by the Heck reaction. During the development of this synthesis, attempts were made to introduce the oxygenation present at C —13 at an earlier stage [27]. Enol ethers 72 and 74 were prepared and subjected to Heck conditions. 

The iridoid sesquiterpene (-)-specionin, an antifeedant to the spruce budworm, was synthesized by T. Hudlicky et al. using the low-temperature vinylcyclopropane-cyclopentene rearrangement as the key step. The substituted cyclopentenone precursor was first exposed to the lithium dienolate derived from ethyl 4-(dimethyl-fert-butylsilyloxy)-2-bromocrotonate at -110 °C to afford silyloxyvinylcyclopropanes as a mixture of exo and endo isomers (with respect to the vinyl group). The mixture was not separated but immediately subjected to TMSI/HMDS, and the corresponding tricyclic ketones were obtained in good yield. Similar results were obtained when TBAF in THF was used instead of TMSI. 

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