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

Pentacyclo6. 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 pentacyclo5. 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 .