Addition bicyclic olefins

Unlike the oxymercuration of acyclic olefins, oxymercuration of bicyclic olefins often gives jy -addition products. Norbornenes 93, for example, show exclusive fvo-oxymercuration. In this reaction, the ratio between the isomers depends on the nature of the fvo-substituent (R1) and tro/o-substituent (R2) (Equation (36)). The presence of electron-withdrawing fvo-substituents always leads to a much greater selectivity in favor of 94a-d over 95a-d.116 117 As indicated by extensive theoretical calculations, the charge distribution in the transition states governs the selectivity of these reactions.118... 

Jefford Gunsher Hill Brun Le Gras Waegell Org. Synth. VI, 142. For a review of the addition of halocarbenes to bridged bicyclic olefins see Jefford Chimin 1970, 24, 357-363. 

An unusual 1,4-addition of a dihalocarbene to 1,2-bis-methylenocycloalkanes (e.g. Ill and 113) gave bicyclic olefins which could then be converted into [5.3.1] (112) and... 

The two-step reaction is useful for the hydration of cyclic and bicyclic olefins because it gives predominantly alcohols epimeric with those obtained by addition of a Grignard reagent to the corresponding ketones.40 Therefore hydration of the intermediate mercurial occurs predominantly from the less hindered side. 

Somfai and Ahman have applied an intramolecular allyl silane addition to an AT-sulfonyl iminium ion as a key step in an alternative synthesis of (+)-anatoxin A [43]. Thus, L-pyroglutamic acid-derived compound 55 was homologated to aldehyde 126 and then to allyl silane 127 (Scheme 24). Using titanium tetrachloride, 127 could be cyclized in good yield to bicyclic olefin 128, which was converted to the alkaloid. 

The ring-opening polymerization of a simple cyclic olefin such as cyclooctene yields two structures of maximum order, which are distinguished by the configuration (cis or irans) of their main-chain olefins. In contrast, polymers made from bicyclic olefins such as norbornene are inherently more complicated and have four structures of maximum order (Scheme 24). In addition to cis- and trans-olefins, the polymers can also be isotactic or syndiotactic. The stereochemistry of these polymers becomes even more complicated when the monomer is asymmetric, since head—head, head—tail, and tail—tail regioisomers are possible. Nevertheless, single-site metathesis catalysts have been developed that can control polymer stereochemistry to an impressive degree by both chain-end and site-control mechanisms. ° ° ... 

MODEL STUDIES Early in this study it appeared that [2.2.1]bicyclic olefin resins added conventional crosslinking thiols in a rapid, exothermic, manner. These results appear to contradict earlier reports that internal olefins and cyclic olefins such as cyclohexene and cydopentene react only slowly with thiols. In reality, [2.2.1]bicydic olefins represent a separate dass of reactive olefins. These results are also consistent with reports (16-19) that bicyclic olefins such as norbomadiene are quite reactive to the addition of monofunctional thiols and thiyl radicals. In order to quantify the relative reactivity of norbornene resins with other "standard" ene components, a model study of the addition reaction was undertaken. A "typical" thiol (ethyl mercaptoacetate) was examined in a series of competitive reactions in which there was a defidency of olefin (Figure 4). Olefin substrates that were compared were norbornene, styrene, butyl vinyl ether, [2.2.2]bicydooctene and phenyl allyl ether. The results of that study are listed below in Table I. 

These results are probably due to a combination of several effects. The enhanced reactivity of the [2.2.1]bicyclic system is most likely due to a steric ring strain factor (16-18) which is complicated by a stereodectronic effect (19). In addition to these factors, it is probable that the kinetics of the initial addition of thiol or thiyl radical to the olefin is "less reversible" in the case of [2.2.1]bicyclic olefins This was confirmed by our model studies described above. The product distribution in the competitive reaction studies was essentially invariant with reaction temperature in the range of 10°C - 90°C There appeared to be no equilibration of the discreet olehn thiol adducts. 

THERMAL ANALYSIS STUDIES The results of our model study indicates that [2.2.1]bicyclic olefins do exhibit a high relative reactivity to the addition of thiols. We have also initiated a study of the polymerization reaction with differential photocalorimetry (photo DSC). The results of this study indicate that the enthalpy of the photopolymerization increases to a maximum of ca. 224 J/g at 320°K and decreases thereafter as the temperature continues to increase (illustrated in Figure 9). The enthalpy per equivalent of ene and thiol is roughly 100,000 J/eq (23.9 Kcal/eq) at 320°K. 

Consequently, the interconversion of classical cations at a rate comparable with capture by a nucleophile (Brown) is not valid here since it is in chlorides and not in acetates that the less homogeneous deuterium distribution should have been expected. The authors maintain that the HX-type reagents are added to nor-bomene and some other similar bicyclic olefins both through intermediate formation of nonclassical ions and by simultaneous cyclic processes. As concerns Brown s data on the addition of HQ and CHjCOOH to 7,7-dimethylnorbomene, Cristol believes them to be inapplicable to unsubstituted norbornenes since in the 7,7-di-methylnorbornene the simultaneous processes are strongly hindered. Cristol s objections, however, are hardly convincing because epoxidation, hydroboration etc. proceed in the case of 7,7-dimethylnorbomene as weU though they only result in endo products. 

If bicyclic olefins are used, addition may occur on either side of the molecule exo- or mdo), and if the two substituents of the carbene are different, again two... 

Shea et al. investigated whether strain involved in alkenes affects reactivity and regiochemistry of the intermolecular 1,3-dipolar cycloaddition reaction [14]. Therefore, the addition of picryl azide (18) with a series of mono-and bicyclic olefins including frans-cycloalkenes and bridgehead alkenes was studied (Scheme 5). In the cases of czs-cyclooctene (16) and ci5-cyclononene (17), decomposition of the initially formed cycloadducts 19 and 20 followed... 

Meanwhile, norbomene being a bicyclic olefin can be polymerized also via an addition scheme with opening of the double bonds. This reaction proceeds in the presence of Ni or Pd catalysts and results in polymers with entirely different structures and, hence, different properties (Scheme 3.1). 

The photochemical addition of cycloheptatriene to 1,4-naphthoquinone yields a small amount of the [6 + 2] product (364) as well as two spiro-ethers and a cyclo-butane. The cycloaddition of 1,4-naphthoquinone to norbornene and bicyclo-[2,2,2]oct-2-ene produces variable amounts of the usual (2 + 2) adducts and low yields of the novel 2 1 adducts (365 n = 1 or 2). It is thought that because of the inherent strain present in these bicyclic olefins, interaction of the intermediate 1,4-biradical by a second quinone molecule competes successfully with the normally... 

The addition of azides to strained bicyclic olefins also affords the expected [3+2] cycloadducts. For example, the addition of phenyl azide to norbomene is remarkably accelerated in water . Also, addition of azides to bicyclic nitroso Diels-Alder adducts 63 affords the [3+2] cycloadducts as a mixture of the two stereoisomers 64 and 65 (about 1 1) in virtually quantitative yields . 

MisceUaneous Polycyclic Systems.—Formation of cyclopropane rings by carbene addition to olefins, and subsequent elaboration by rearrangement or addition reactions, is an important method of generation of both polycyclic and bicyclic systems. Examples of carbene additions are shown in Scheme 43 296,298—301,304 Subsequent transformation by reduction or rearrangement as noted in Scheme 44 is possible. Not only does lithium aluminium... 

Figure 27 Bicyclic olefins that can be polymerized by metallocene catalysts via addition.

Brown, H. C., and K.-T. Liu Additions to Bicyclic Olefins. VII. Electrophilic Addition of Hydrogen Chloride and Deuterium Chloride to Norbornene, 2-Methyl-norbornene, and Related Bicyclic Olefins. Evidence for a Carbonium Ion Process and the Capture of Unsymmetrical (Classical) 2-Norbornyl Cations. J. Amer. Chem. Soc. 97, 600 (1975). 

The mechanism of this reaction has not been studied in detail. However, it can be represented as a sequence of reactions. The first reaction is, in fact, [3+ 2]-cycloaddition of olefin to furoxan (161). Under severe conditions, the resulting intermediate A undergoes fragmentation to give five-membered cyclic nitronate B. The latter is involved in the usual addition reaction with an excess of olefin to form isolable bicyclic product (162) (301, 378, 379). 

Using a protocol for tandem carbonylation and cycloisomerization, Mandai et al.83 were able to synthesize cyclopentene and cyclohexene derivatives in high yield, including fused and 5/>/>0-bicycles (Scheme 25). The cyclohexene Alder-ene products were not isolable methanol addition across the exocyclic double bond (in MeOH/ toluene solvent) and olefin migration (in BuOH/toluene solvent) were observed. The mechanism of methanol addition under the mild reaction conditions is unknown. In contrast to many of the other Pd conditions developed for the Alder-ene reaction, Mandai found phosphine ligands essential additionally, bidentate ligands were more effective than triphenylphosphine. 

Finally, production of tricyclic array 153 (Scheme 24) required cyclization of bicyclic ester 151 in which additional oxygenation was present in the olefinic appendage. The successful conversion to enol ether 152 demonstrated further the power of the method and led to the JKF fragment 153 [34b]. 

Bicyclic derivatives. Polyhydroxylated carbo-bicyclic derivatives may be regarded as carbasugars with the rigid structure resulting from the presence of the additional carbocyclic ring. The most convenient way for construction of the bicyclic skeleton consists of the Diels-Alder reaction of properly functionalized trienes (intramolecular version) or dienes and olefins (intermolecular). 

The anion radical species formed by the electroreduction of aliphatic esters show interesting reactivities, and the reduction of olefinic esters gives bicyclic products with high regio- and stereoselectivity. The electroreduction of the ester in the presence of chlorotrimethylsilane affords a tricyclic product (Scheme 21) [35, 40]. The mechanism of this cyclization reaction seems to be the addition of anion radical species, formed by the reduction of the ester group, to the carbon-carbon double bond. 

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