Bicyclooctanes: cis-bicyclo[3.3.0]octa-2,6 and 2,7-diene-2-carboxylic acids

Rh2(II)-Catalyzed Ring Expansion of Cyclobutanol-Substituted Aryl Azides To Access Medium-Sized N-Heterocycles

“…The specificity of the [1,2] migration step was investigated with aryl azides 10e – 10j (entries 5–10). In contrast to related ring-expansion reactions of substituted cyclobutanols containing N 2 as the leaving group, our reaction proved to be selective: each substrate submitted to the reaction conditions produced the medium-ring N -heterocycle as a single constitutional isomer. Aryl azides 10e and 10f exhibited exclusive migration of the benzyl carbon over the methylene (entries 5 and 6), while only allyl carbon migration was observed with aryl azide 10g to provide benzazepinone 11g as the only product (entry 7).…”

“…Loss of the rhodium carboxylate produces the benzazepinone product. Alternatively, the key [1,2] migration step could occur at the same time as loss of dinitrogen: coordination of the rhodium carboxylate to the γ-nitrogen in 17 activates the substrate for a semi­pinacol ring expansion with concomitant loss of N 2 to produce 13 …”

Ring Expansion of Cyclobutylmethylcarbenium Ions to Cyclopentane or Cyclopentene Derivatives and Metal-Promoted Analogous Rearrangements

“…In research on bicyclooctanes, ring expansion of bicyclo-[3.2.0]hept-2-en-6-one 486 using 1 equiv of diazomethane in the presence of 0.5 equiv of lithium perchlorate in diethyl ether at À78 °C for 10 min and subsequently at room temperature for 1 h provided a mixture of two regioisomers 481 and 482 in a 4:1 ratio (Scheme 135). 182 The desired bicyclo[3.3.0]oct-2-en-6-one 481 was isolated from the mixture in 44% yield. In the absence of a Lewis acid, the observed ratio was ∼3:2.…”

“…182 The desired bicyclo[3.3.0]oct-2-en-6-one 481 was isolated from the mixture in 44% yield. In the absence of a Lewis acid, the observed ratio was approximately 3:2.…”