Olefins diene adducts

Hexafluoroacetone is a reactive electrophile. It reacts with activated aromatic compounds (e.g., phenol), and can be condensed with olefins, dienes, ketenes, and acetylenes. It forms adducts with many compounds containing active hydrogen (e.g., H.,0 or HCN). Reduction of HFA with NaBH or LiAlH affords the useful solvent hexafluoroisopropyl alcohol. The Industrial importance of HFA arises largely from its use 1n polymers and as an... 

The reaction of diene adducts with oxidants has also been studied. In both cases cis insertion of the Pd(II)-carbon bond into the second olefinic bond occurred. Thus Stille et al. 126) found that reaction of the norbornadiene(methoxy) adduct or the norticyclyl(methoxy) adduct with CI2 or with Brg in CH3OH gave 3-cx o-methoxy-5-halometricyclenes plus the dimethoxy adduct ... 

Cycloaddition reactions of (E)-l-acetoxybutadiene (18a) and (E)-l-methoxy-butadiene (18b) with the acrylic and crotonic dienophiles 19 were studied under high pressure conditions [9] (Table 5.1). Whereas the reactions of 18a with acrylic dienophiles regioselectively and stereoselectively afforded only ortho-enJo-adducts 20 in fair to good yields, those with crotonic dienophiles did not work. Similar results were obtained in the reactions with diene 18b. The loss of reactivity of the crotonic dienophiles has been ascribed to the combination of steric and electronic effects due to the methyl group at the )S-carbon of the olefinic double bond. 

The Diels-Alder reaction between the diene 87 and the olefin 88 afforded the adduct 89 in good yield (Fig. 30).45... 

Af-Acyliminium ions are known to serve as electron-deficient 4n components and undergo [4+2] cycloaddition with alkenes and alkynes.15 The reaction has been utilized as a useftil method for the construction of heterocycles and acyclic amino alcohols. The reaction can be explained in terms of an inverse electron demand Diels-Alder type process that involves an electron-deficient hetero-diene with an electron-rich dienophile. Af-Acyliminium ions generated by the cation pool method were also found to undergo [4+2] cycloaddition reaction to give adduct 7 as shown in Scheme 7.16 The reaction with an aliphatic olefin seems to proceed by a concerted mechanism, whereas the reaction with styrene derivatives seems to proceed by a stepwise mechanism. In the latter case, significant amounts of polymeric products were obtained as byproducts. The formation of polymeric byproducts can be suppressed by micromixing. 

In general, transition metal-catalyzed addition reactions to 1,3-dienes gave 1,4-adducts via 7t-allyl metal intermediates.23 The ar //-Markovnikov 1,2-addition mode of this reaction is therefore unusual (Scheme 17). It was noted that the configuration of the 3-olefin was retained with either ( )- or (Z)-1,3-dienes. The observation that the 3-olefin was unimportant for this reaction strongly suggests that the method could be applicable to unactivated alkenes. 

Wang and Sutherland95 communicated an autocatalytic Diels-Alder reaction in which the adduct of diene 113 and olefin 114 catalyzed its own formation. This was accomplished through binding of both reactants in a pre-organized fashion by means of multiple hydrogen bonding (see complex below structures 113 and 114 overleaf). 

Allenes generally react with conjugated dienes to give [4 + 2] type of adducts in contrast with ketenes which generally react with dienes in a [2 + 2] kind of way. Some enhancement of reactivity is expected in comparison with olefins because of the significant amount of strain that allenes have. Semi-empirical calculations, however, have shown allene to be less reactive than ethylene due to higher deformation energies135. 

Selenosulfonylation of olefins in the presence of boron trifluoride etherate produces chiefly or exclusively M products arising from a stereospecific anti addition, from which vinyl sulfones can be obtained by stereospecific oxidation-elimination with m-chloroper-benzoic acid134. When the reaction is carried out on conjugated dienes, with the exception of isoprene, M 1,2-addition products are generally formed selectively from which, through the above-reported oxidation-elimination procedure, 2-(phenylsulfonyl)-l,3-dienes may be prepared (equation 123)135. Interestingly, the selenosulfonylation of butadiene gives quantitatively the 1,4-adduct at room temperature, but selectively 1,2-adducts at 0°C. Furthermore, while the addition to cyclic 1,3-dienes, such as cyclohexadiene and cycloheptadiene, is completely anti stereospecific, the addition to 2,4-hexadienes is nonstereospecific and affords mixtures of erythro and threo isomers. For both (E,E)- and ( ,Z)-2,4-hexadienes, the threo isomer prevails if the reaction is carried out at room temperature. 

Rhodium catalysis has played a critical role in the development of this type of reaction. The rhodium-mediated [4 + 2] carbocyclization between dienes and unactivated olefins or alkynes is a notable early example of this concept [2]. Further investigations demonstrated the extension of this methodology to the reaction between a diene and an allene [3]. Expansion of the scope of this strategy, to both the intra- and intermolecular [5-1-2] homologs of the Diels-Alder reaction, was accomplished with a vinylcyclopropane and either an alkyne or an olefin to afford the carbocyclization adducts (Scheme 11.1) [4, 5]. 

Electron-deficient 1,3-dienes are potentially interesting Diels-Alder dienes. In our study with different kinds of olefins, we observed that 2-(phenylsulfonyl )-l,3-d1enes show a duality in their Diels-Alder cycloaddition reactions, giving [4+2] adducts with both electron-deficient and electron-rich olefins. This dual reactivity of the 2-(phenylsulfony1)-l,3-dienes in [4+2] cycloaddition increases the role they can play in organic synthesis. 

Anhydrous silver-olefin complexes are readily dissociable, low-melting, and variable in composition 92a, 176, 183). Cyclic olefins and polyolefins form stable complexes with silver nitrate or perchlorate, but again the Stoichiometry of the complexes varies considerably, sometimes depending on the conditions of preparation. The following types have been isolated [Ag(un)2]X (un = e.g., cyclohexene, a- and /3-pinene) ISO), [Ag(diene)]X diene = e.g., dicyclopentadiene 220), cyclo-octa-1,5-diene 50, 130), bi-cyclop, 2,1 ]hepta-2,5-diene 207), and cyclo-octa-1,3,5-triene 52), and [Ag2(diene)]X2 (diene = e.g., cyclo-octa-1,3- and -1,4-diene 180), bi-cyclo[2,2,l]hepta-2,5-diene 1) and tricyclo[4,2,2,0]-decatriene 10)). Cyclo-octatetraene (cot) forms three adducts with silver nitrate 52), viz., [Ag(cot)]NOs, [Ag(cot)2]N03, and [Ag3(cot)2](N03)3. On heating, the first two lose cyclo-octatetraene and all three decompose at the same temperature. From the stoichiometry of the above complexes it appears that the... 

The Diels Alder reaction of the acyclic diene and 146 may result in unexpected products, however. As reported by Ried, the reaction of 1,4-diphenylbutadiene and 146 may, under drastic conditions, give the aromatized compound (148) and l,3,4,7-tetraphenylbenzo[c]furan (149) in varying amounts, depending on the conditions. In methylglycol/propanol (6 hr reflux) a substance was isolated (mp 147-148°C, 59%) which has tentatively been formulated as 150. One final goal of the sequence described seems to be unaffected by these anomalous reactions, however Diels-Alder adducts of benzo[c]furans can be obtained in a one-step reaction from a diene, 146, and an appropriate olefinic compound in acetic acid/acetic anhydride as shown in Eq. (7). ° ... 

Photodimerization involves 1 1 adduct formation between an excited nd a ground state molecule. Olefinic compounds, aromatic hydrocarbons, conjugated dienes, oc-unsaturated compounds are known to dimerize when Cxpdsed to suitable radiation. Photodimerization of olefinic compounds Can occur by either (a) 1,2-1,2 addition, (b) 1,2-1,4 addition or... 

The photochemical addition of simple olefins to a,/ -unsaturated ketones is a reaction of great current interest.113 The steroidal A16-20-ketone system is especially prone to cycloaddition under mild conditions. Sunder-Plassmann et al114,115 irradiated 3/ -acetoxypregna-5,16-dien-20-one (67) in the presence of tetrafluoroethylene and obtained a 2 1 mixture of the a- and / -face adducts (68) and (69) together with a third adduct which has been characterized as (70) by X-ray crystallographic analysis.1153... 

Photosensitized dienes also add to simple olefins the relative amount of 2 + 2 and 2+4 addition product again depends on the energy of the triplet sensitizer. For example, in the photosensitized addition of butadiene to tri-fluorethylene (Equation 13.61), the percentage of the 2 + 4 adduct (52) increases from 0.5 percent when acetophenone is used as the photosensitizer to 22.5 percent when fluorenone is the photosensitizer.79... 

Regioisomerism in azide additions is also evident in unsymmetrical dienes with two unequally strained double bonds.89,92,144 Reaction occurs preferentially at the angle-strained double bond,25,81,89-92 and two isomeric exo-monotriazoline adducts are obtained.81,93 The ratios of the triazoline isomers from the reaction of phenyl azide and bicycloocta-2,6-diene, as deduced from their NMR spectra, indicate that the major isomer is the one that results from the terminal azido nitrogen attacking the olefinic carbon more removed from the unreactive double bond (Scheme 10).92 Similar reactions... 

Vinylbenzofurans also react as dienes in Diels-Alder reactions with acyclic olefins. The 3-vinylbenzofiirans 174,175, and 176 gave the normal adducts resulting from (4ir+27r)-cycloaddition in its reaction with TCNE. A by-product from the reaction of the diene 174 and TCNE was the cyclobutane 177 (91AJC1085). 

This procedure illustrates a recently published, simple, general method for the synthesis of conjugated dienes from olefins. The scope of the reaction is shown in Table I.5 In most of these examples hydrogen bromide. .elimination can be effected by stirring a solution of the olefin-bromo-methanesulfonyl bromide adduct in methylene chloride with one equivalent of triethylamine at room temperature. Only two equivalents of the more costly potassium tert-butoxide are then needed in the second elimination step the yields using the two-base procedure are generally superior to that obtained using only potassium tert-butoxide. 

---