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Photochemical Synthesis and Reactivity of Strained Polycyclic Cyclobutenes. A2(~)-Tricycl0[4.2.1.0~~~]nonene~
Table I. Quantum Yield for Ring Closure and Activation Energy for Ring Cleavage of Cyclobutenes
x
photocyclizaQuan- tion Activatum yield tion diene yielda (glpc) energy yield
Sir: Synthesis of highly strained polycyclic cyclobutenes, 1 and 2, and strained propellanes,3 3 and 4, has been of
7
0.12b 1
3
2
4
much interest because of the unusual hybridization, and reactivity of such molecules. We bonding, present here an attractive photochemical route to strained polycyclic cyclobutenes which has led to the synthesis of A2(5)-tri~y~lo[4.2. l.O2r5]nonene (5). Addition reactions and the rate of thermal ring opening of 5 suggest that it is intermediate in strain energy between 1 and 2. Epoxidation of 5 has led to the new strained propellane 6 .
9
10
8
1
7lC
36.0d
lOOd
0.11
>95
32.7e
57f
0.11
>95
30.4e
58f
3e3f
'I
5
-m 13
