Silver-catalyzed ring expansion

The structure of the product obtained by the silver(I) ion catalyzed ring expansion of anti-1-chloro-2,3-benzo-7-azabicyclo[2.2.l]hepta-2,5-diene, formulated tentatively as 1-methoxy-l/f-1-benzazepine,140 has been shown to be 2-methoxy-6,7-benzo-l-azabicyclo[3.2.0]hept-3-ene... 

TABLE 8.11. Scope of Silver-Catalyzed Cyclopropyldiazoacetate Ring Expansion... 

Ring expansion reactions of the type shown in equations (17) and (18), in which a more equitable distribution of carbon atoms between two rings of a polycyclic hydrocarbon is produced, provide the link between the decyclization reactions above and the annulation reactions considered later. It would seem that the greater the strain in the reactant, the larger the number of potential catalysts. The complexes of seven different metals catalyze the reaction shown in equation (17). Of the possible catalysts, only the silver (I) salts bring about any byproduct formation. The isomerization of [l.l.ljpropellane (equation 18) is catalyzed by [RhCl(PPh3)3]. ... 

With compound 64 available, vanadyl acetylacetonate catalyzed epoxidation [44] accompanied by simultaneous cyclization, afforded the corresponding tetrahydrofuran and its diastereomer in a 4 1 ratio (Scheme 12). Ring expansion of the corresponding mesylate 65 with silver (I) carbonate afforded compound 66 in a 42% yield for the two steps [45]. Extension of the side chain in six steps, followed by an asymmetric epoxidation, gave product 67 stereoselectively. The cyclization of 67 with titanium tetraisopropoxide in a manner consistent with model studies [27d], afforded bicyclic ether 68 in 65% yield. Transformation to the epoxide under standard conditions afforded fragment 69 ready to be coupled with the D-ring side chain. 

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