engleski

Synthesis and cycloaddition properties of 7-thianorbornenes

Thiophene has been reacted under high-pressure and temperature with N-methylmaleimide and N-phenylmaleimide to produce Diels-Alder exo- and endo-adducts. Reaction of 7-oxanorbornadiene-2, 3-dicarboxylic anhydride, a highly reactive dienophile, with thiophene occurred under high-pressure even at room temperature to yield stereoisomeric 1:1-adducts by site selective attack at the maleic anhydride type of pi-bond. This approach afforded the first examples of syn- and anti- heterobridged sesquinorbornadienes containing a sulfur bridge. Similar reaction of isobenzothiophene was even more facile as reaction occurred at room temperature and atmospheric pressure to yield its benzoanalogues. Thermal fragmentation involving loss of furan and sulfur occurred from both classes of adducts under FVP conditions (370 0C, 0.005 mbar) to produce phthalic anhydride or naphthalene-2, 3-dicarboxylic anhydride respectively. The putative 7-thianorbornadiene intermediates, generated by loss of furan, were not detected. Reaction of exo-N-methyl 7-thianorbornene-5, 6-succinimide with the ester-activated cyclobutenoaziridine provided access to CNS-[3]polynorbornane, while similar addition of the exo, endo-isomer of O, S-benzosesquinorbornadiene afforded the CNOS-[4]polynorbornane. These are the first S-bridged [n]polynorbornanes to be reported and their cycloaddition reactions will be also reported.

Reactions under high pressure; Diels-Alder reactions; stereochemistry; cycloadditions

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