Tandem Ring Enlargement by Two Carbon Units from the Bicyclo[3.3.0]octane to the Bicyclo[5.5.0]dodecane System

New Tandem Ring Enlargements of Bicyclo[3.3.0]octanes to Bicyclo[5.5.0]dodecanes and Subsequent Conversions into Tricyclo[5.5.0.0.2,9]dodecane and Tricyclo[5.5.0.02,10]dodecane Derivatives

“…Thus, as in our previous study, [2] the synthesis ended one step short of the target molecule 19, because the last precursor possesses too many functional groups. This, however, was a necessary prerequisite of the chosen reaction pathway.…”

“…[2] One-pot twofold double ring-enlargement should transform compound 1 into suitably substituted bicyclo [5.5-.0]dodecatetraenes such as A. These are potential precursors of (substituted) tetracyclo [5.5.0.0 4,10 ]dodecatetraene (B), which in turn is related to the unknown C by an unusual photochemical process predicted over 30 years ago by Woodward and Hoffmann which is still under discussion today.…”

“…[3,4] In the beginning, it seemed to be most efficient for our purposes to apply known methods for cyclopentanone Ǟ cycloheptanone transformations using [2ϩ2] additions as one-pot processes, and indeed the reaction of the bis(enamine) of 1 with certain alkynes allowed for the preparation of A-type compounds (Scheme 1). [2] Unfortunately, in our earlier work further conversions led to an unwanted intramolecular reaction. We now report initial dichloroketene/1-silylenol ether cycloadditions.…”

“…The fact that the product mixture did not mirror the starting material composition can be explained similarly to the cycloadditions of the enamines derived from 1. [2] Depending on the conditions, 5 could be dehalogenated by tributyltin hydride/AIBN to give either dichloro diketone 6 or the chlorine-free 7. The stereochemical structure assignment of 6 was based on the relatively large ''W-type'' coupling of 4.6 Hz between 2-H and the 4-H in the NMR spectrum.…”

“…Figure 1. Single-crystal X-ray structure of 9-hydroxy-5,11-dimethyltricyclo[5.5.0.0 2,9 ]dodeca-4,10-dien-3-one (13) [19] Figure 2. Single-crystal X-ray structure of 3,9-dimethyltricyclo-[5.5.0.0 2,9 ]dodec-3-ene-5,11-dione (14) The formation of the novel cage compounds can be rationalized by starting with the transformation of 10 into 11, and subsequently into 12.…”