Transannular participation

Transannular participation of a triple bond has been examined by Hanack and Heumann (86). Acetolysis or solvolysis in aqueous acetone of cyclodecyn-5-yl-l-tosylate 104a gave, besides some unidentified unsaturated hydrocarbons, a mixture of the rearranged ketones 105 and 106. None of the unrearranged... 

Finally, in contrast to the reactions reported above, 49 reacts131 with dimethyl(methyl-thio)sulfonium fluoroborate (DMTSF) and triethylamine tris(hydrofluoride) in dichlorome-thane to give only 5% of the 1,2-addition product 122. The main products, present in 73 27 ratio, are the exo-exo and endo-exo adducts 123 and 124, formed by exclusive exo attack of the electrophile on the double bond, followed by transannular -participation in the intermediate bridged cation and final addition of fluoride to the nortricyclic cation from both the exo or endo side (equation 120). 

Simple 1,2-additions to this compound have been observed123131132 also in other sulfenylation reactions, and in other electrophilic additions involving strongly bridged intermediates. Although these results have been interpreted as evidence that additions of sulfenyl halides to symmetrical alkenes do not involve open carbenium ions before the product-determining step, the different behavior observed in the case of 49 suggests123 that close proximity is necessary to have transannular participation of 7r-bonds, at least in additions of sulfenyl derivatives and of some other electrophiles carried out in the presence of efficient nucleophiles. 

A tricky formation of a cyclobutane by transannular participation of a double bond was observed in the photochemical dcnitrogenation of 4,5-diazatetracyclo[6.2.1.1 3,6.02-7]dodeca-4,9-diene (20). The formation of the tricyclic diene 22 in addition to the expected cyclopropane 21 can be rationalized as a formal homo Cope rearrangement in the intermediate diradical.42... 

Furthermore, it has been found that larger carbocyclic 1,5-dienes195 or norbornadiene96,173 196 give halofluorinations with transannular participation of the second re-bond. A synthetically interesting example of a comparative study of selectivities in bromofluorinations of unsaturated... 

The electrophilic anti- 1,2-addition of the elements of MeSF to C=C has been achieved by a one-pot reaction of Me2S+-SMe BF4- and Et3N.3HF with various types of alkenes267. Markovnikov products arise from unsymmetrically substituted olefins. The reaction of 2,6-norbomadiene proceeds with exclusive exo-attack on one double bond followed by participation of the second double bond to give rise to two isomeric 3,5-disubstituted nortricyclanes267. By contrast, no transannular --participation has been observed with 1,5-cyclooctadiene. The reaction is believed to occur via the corresponding thiiranium species267. 

H. Yuasa, J. Tamura, and H. Hashimoto, Synthesis of per-O-alkylated 5-thio-D-glucono-l,5-lactones and transannular participation of the ring sulphur atom of 5-thio-D-glucose derivatives on solvolysis under acidic conditions,./. Chem. Soc. Perkin Trans., 1 (1990) 2763-2769. 

The steric course of the above deoxyribosylations might be explained by the formation of the cation (52) which is readily attacked by a nucleophile from the a-position. An attack from the opposite side is hindered by the bulky p-toluyl group at position 5 of the sugar moiety. Moreover, the cation (52) might be stabilized by a transannular participation of the C-5-p-toluyl group with the formation of the... 

Okfin eycUzatUm. (Z,Z)-l,5-Cyclononadiene (1) reacts with benzeneselenenyl chloride in acetic acid buffered with NaOAc with transannular participation by the remote double bond to afiord 2 in 68% yield/ Under these conditions, geranyl acetate (3) does not afiord 6, but rather the usutd olefin addition products 4 and 5. Cyclization of 4 to 6 does occur on treatment with CF3CO2H in CH2CI2 the seleniranium ion a is probably an intermediate, since the compound analogous to 4 but lacking the CsHsSe— group fails to cyclize under these conditions. ... 

Various protected bicyclic 2,5-anhydro derivatives of 5-thio-D-mannitol were obtained from methyl 2,3,4-tri-(9-acetyl-6-(9-mesyl-5-thio-a-D-glucopyranoside by transannular participation of the ring sulfur atom and ring opening of the thiiranium ion [35]. Similar reactions were earlier observed with, for example, a 4-(9-methanesulfony 1-5-thio-D-xylopyranose [36]. 

One exception to this generalization is the formation of the cis hydroxyacid by the hydrogenation of 4-carboxycyclohexanone (24) over Raney nickel in base (Eqn. 18.20).57 The production of this stereoisomer is probably the result of transannular participation by the carboxy group. 

On the other hand, as mentioned briefly in Volume VI, page 150, 3j8-tropanyl chloride (LXIa Y = C1) is converted by potassium cyanide into a pyrrolidine (LXVIII), while the 3a-epimer gives the 3a-cyano-tropane due, presumably, to a transannular participation of the ring... 

Even the cyclopropane-diazonium ions (4<59)366 367 and (474)368 decompose with participation by the double bond. The hydrolysis of bicyclo [4.3.1] dec-6-en-l-yl p-nitrobenzoate (475) is accelerated by a factor of 120 and affords, inter alia, the tricyclic alcohols (47<5)369. A related case of transannular participation, leading to ion pair return, was observed with 5-cyclodecen-l-yl p-nitrobenzoate (7 >4)112 (Section 4.2.3). 

Transannular participation of n-bonds takes place in the solvolysis of esters of (Z)-cyclooct-3-enol to give bicyclic derivatives containing three-membered rings. Thus, acetolysis of 4-(4-bromophenylsulfonyloxy)cyclooctene followed by hydrolysis of the product mixture gave endo-and exo-bicyclo[5.1.0]octan-2-ol (1), in 39 and 13% yield, respectively. The predominant formation of the cntfo-bicyclooctanol is consistent with a concerted process. ... 

In electrophilic addition reactions, transannular participation by an oxirane to form an oxonium ion occurs in medium-ring cycloalkenes. Thomas first investigated this transannular addition in epoxide 73 [86]. Treatment with iodine gave iodinated bicyclic ethers 74 and 75, Eq. 58. 

In unsaturated hydrocarbon systems where Wagner-Meerwein-type rearrangements, transannular hydrogen shifts or transannular -participations are possible, such reactions do occur. Moreover, in the bromofluorination of 9-oxabicyclo[6.1.0]non-4-ene, a transannular reaction involving oxygen participation has been observed. ... 

Transannular participation of ether oxygen has also been identified by kinetic studies of some cyclic ethers. The series 11-14 has been studied, and the data... 

Transannular participation of ether oxygen has also been identified by kinetic studies of some cyclic ethers. The series 11-14 has been studied, and the data obtained indicate a very large acceleration in the case of replacement of the 5-CH2 with oxygen in a cyclooctyl ring. The huge difference in rate that results from the... 

One early example was reported by Chatteijee in 1979 for stereospecific synthesis of the sesquiterpene isocomene by transannular cationic cyclization. The acid-catalyzed cyclization of epoxide 152 through transannular participation of the remote double bond led to the formation of 153 (Scheme 20.37), which was further transformed to isocomene. The reaction was stereoselective since formation of any other diastereomers will lead to the formation of much strained polycyclic systems with trans-fased cyclopentanes. 

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