Transannular cyclizations, benzene

The tandem cyclization-cycloaddition reaction of 1-diazoacetyl-7,7-dimethylbicyclo[2.2.1]heptan-2-one (1) with dimethyl butynedioate catalyzed by rhodium(II) acetate dimer in benzene at 25 °C, afforded a formal [3 + 2] cycloadduct 2 in 85% yield with complete diastereofacial selectivity48. This reaction is interpreted to proceed via rhodium carbenoids and subsequent transannular cyclization of the electrophilic carbon onto the adjacent oxo group to generate a cyclic carbonyl ylide. followed by 1,3-dipolar cycloaddition. Similar reactions are observed with other dipolar-ophiles, such as propargylic esters and A -phenylmaleimide. Studies dealing with the geometric requirements of dipole formation were undertaken. 

It was thus of interest to determine whether a transannular addition could occur for the cyclo-octenyl radical. The cyclo-octenyl radical has been prepared from its parent halohydrocarbon in several matrices in the rotating cryostat. At 77°K the radical was stabilized in all of the matrices but when the samples were warmed reaction took place. The e.s.r. spectra showed that the main reaction in matrices of water, benzene or camphane was hydrogen abstraction adjacent to the double bond to give a cyclic allyl radical (9) rather than the bicyclic radical. However, in a matrix of bicyclopentadiene dimer cyclization occurs to give the bicyclic radical and in a matrix of adamantane both allylic and bicyclic radicals were formed. 

Dimethylcyclo-octa-1,5-diene reacts with boron trifluoride diethyl etherate to give 2,5-dimethylbicyclo[3,3,0]oct-2-ene (60%), whereas l,5-dimethylbicyclo[3,2,l] octan-8-ol (156 R = H 50%) and its tosylate (156 R = Ts 70%) are formed on treatment with perchloric acid-aqueous dioxan and toluene-p-sulphonic acid, respectively. Preliminary results indicate that cis,ci -cyclo-octa-l,5-diene and hydrogen peroxide-mercury(ii) nitrate react to give a transannular peroxide. The boron trifluoride diethyl etherate-benzene catalysed cyclizations of the cyclo-octenyl ester (157 R = COjEt) and ketone (157 R = COMe) to the bicyclo[3,3,l]nonanes (158 R = C02Et) and (158 R = COMe), respectively, have been studied further. Possible intermediates in these reactions were synthesized but no cyclized products were obtained. The mechanism that was finally suggested involves protonation of the... 

An interaction of the intermediate carbon-centered radical (A) with a neighboring carbon-carbon bond in this ring expansion leads to a transannular radical cyclization the treatment of the unsaturated decanols with (diacetoxyiodo) benzene-iodine followed by irradiation underwent fragmentation of intermediate allyloxy radicals (A) to give the bicyclo(5.3.0]decanones (40-78%) and to give the 7,5,5-tricycKc compound (81%) by way of a Billiard reaction, as outlined in Scheme 687 ... 

---