The thermal addition of
N-carbobenzyloxyisoindole (
N-Z isoindole)
11a, generated by the reaction of 3,6-di(2-pyridyl)-
s-tetrazine
9 with
N-Z 7-azabenzonorbornadiene
8a, onto dimethyl tricyclo[4.2.1.0
2.5]nona-3,7-diene-3,4-dicarboxylate
17 occurred site selectively at the cyclobutene -bond to form a stereoisomeric mixture of 1 : 1-adducts
18 and
19, in which the bent-frame isomer
19 was dominant (ratio 5 : 1). In contrast,
N-benzyl tetrafluoroisoindole
11c reacted with
17 only under high-pressure conditions (14 kbar, RT, 4 days) to afford 1 : 1-adducts at the cyclobutene site, in which the extended-frame isomer
18c was dominant and the accompanying bent-frame product
19c reverted to starting materials soon after isolation. These same stereoselectivities were used to prepare "windscreen wiper" compound
28c having two mobile
N-benzyl substituents attached to a rigid scaffold by the reaction of
N-benzyl tetrafluoroisoindole
11c with tetramethyl tetracyclo[4.4.1.0.
2,5.0
7.10]undeca-3,8-diene-3,4,7,8-tetracarboxylate
23. Cavity bis-(cyclobutene-1,2-diester)
6 reacted with
N-benzyl tetrafluoroisoindole
11c twice over to produce cavity structure
36 with two
O- and two
N-benzyl bridges on the inner face, whereas the narrower cavity bis-alkene
32 stopped at the 1 : 1-addition stage. The dynamics of the Z-group in the dual adducts
26a–
28a are discussed briefly and key adducts and cavity systems have been structurally evaluated by X-ray crystallography, VT NMR, and molecular modeling.
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