Synthesis and Chemical Transformations of 4, 5‐Homosnoutene Derivatives: An Attempted New Access onto the (CH) 12 Energy Hypersurface

Pentacyclo[6. 4. 0 2, 4 . 0 3, 10 . 0 7, 9 ]dodeca‐5, 11‐diene( 4 ) is proposed as new potential precursor of the truncated tetrahedrane 1 . The synthesis of several new pentacyclo[5. 4. 0. 0 2, 4 . 0 3, 9 . 0 6, 8 ] undec‐10‐ene (4, 5‐homosnoutene) derivatives including homosnouten‐5‐one( 10 ), 5‐methylidenehomosnoutene( 19a ) as well as homosnoutene‐5‐carb‐aldehyde( 17b ) and their reactions directed toward ring enlargement to the skeleton of 4 are reported. Although all the homosnoutenes resisted ring expansions, several unexpected new polycyclic systems were obtained. Any intermediate developing a cationic center at C(5) of the skeleton of 10 rearranged with release of strain and opening of one or both three‐membered rings to give compounds such as 22 and 23 . The aminomethyl derivatives 13a and 13b, upon diazotation, underwent a remarkable fragmentation to give 10 and homosnouten‐5‐o1(20), respectively. The 5‐(dibromomethyl) homosnouten‐5‐o1( 14 ), upon treatement with t ‐BuLi, rearranged to the pentacyclic ether 15 , while the carbine 11b , generated by the thermal or photochemical decomposition of the tosylhydrazone salt of 17c , solely gave 19a by C, H insertion. The 1, 1‐dicyclopropylethene unit in 19c was excited selectively upon irradiation, but the products 26 and 27 of this photochemical rearrangement were derived only from n‐participation in diradical intermediates 25a‐25c .