Add time:07/11/2019         Source:sciencedirect.com

Nitrosation of 7-oxabicyclo[2.2.1]hept-5-en-2-exo-ylmethyl amine (20) gave 7-oxabicyclo[2.2.1]hept-5-en-2-exo-methanol (22) whereas 7-oxabicyclo[2.2.1]hept-5-en-2-endo-ylmethylamine (21) afforded a 1:1 mixture of 7-oxabicyclo[3.2.1]oct-6-en-2-ols (23) and 8-oxabicyclo[3.2.1]oct-3-en-2-ols (24). Nitrosations of 2-exo- (28) and 2-endo-aminomethyl-7-oxabicyclo[2.2.1]hept-5-en-2-ol (29) gave mixtures of 8-oxabicyclo[3.2.1]oct-6-en-2-one (25) and 8-oxabicyclo[3.2.1]oct-6-en-3-one (37). The preference for the C(3) methylene group migration giving 25 was the best (12:1) in the case of the 2-endo-aminomethyl alcohol 29. Compared with the nitrosations of bicyclo[2.2.1]heptane analogues, the 7-oxa bridge in 28 and 29 enhances the preference for the C(3) methylene group migration vs. the C(1) methine group migration. The Tiffeneau-Demjanov one-carbon ring enlargement reactions of 2-exo-aminomethyl-7-oxabicyclo[2.2.1]hepta-2-endo-ol (30). 2-exo-aminomethyl-5-chloro (32) and 2-exo-aminomethyl-6-chloro-7-oxabicyclo[2.2.1]hept-5-en-endo-ol (33) are also reported. Under kinetically controlled conditions, 8-oxabicyclo[3.2.1]oct-6-en-2-one (25) adds to electrophiles EX=PhSeCl, PhSeBr. 2,4-(NO)2C6H3SCl with high stereo- and regioselectivity giving the corresponding 8-oxabicyclo[3.2.1]-octan-2-ones where E substitutes the exo position of C(6) and X the exo position of C(7).

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