Acid-Catalyzed Transannular Cyclization of 3a<i>H</i>-Cyclopentene[8]annulene-1,4-(5<i>H</i>,9a<i>H</i>)-diones and Some Proposed Mechanisms

Bicyclic 3aH-cyclopentene[8]annulene-1,4-(5H,9aH)-diones underwent three types of acid-induced transannular reactions, Michael cyclization, [3 + 2] cycloaddition, and Friedel−Crafts ipso-alkylation, depending on the cyclopentenone ring substituent (Me or Ph) and the position of [8]annulenone substituent as well as the nature of acids (BF3, MeSO3H, CF3SO3H). The Me-substituent permitted the Michael reaction for all acids used to give tricyclic diones by the activation of cyclopentenone carbonyl group. However, the Ph-substituent inhibited the Michael reaction for BF3 and MeSO3H but allowed the [3 + 2] cycloaddition and Friedel−Crafts reaction for CF3SO3H depending on the position of annulenone substituent. These CF3SO3H reactions exhibited the following novel rearrangements, affording 2-naphthalenone and 7-acenaphthylene derivatives, respectively. The factors that control the reaction mode of these transannular cyclizations were discussed in view of the constraint twist-boat conformation of [8]annulenone ring as well as the ring substituent effects on the intramolecular cyclization. In addition, these [8]annulenone rings were found to easily undergo the intramolecular [2 + 2] photocyclization to provide the tetracyclic cage compounds which exhibited the facile cycloreversion under the influence of acid.双环3aH-环戊烯并[8]轮烯-1,4-(5H,9aH)-二酮（Bicyclic 3aH-cyclopentene[8]annulene-1,4-(5H,9aH)-diones）可依据环戊烯酮环取代基（甲基Me或苯基Ph）、[8]轮烯酮（[8]annulenone）取代基的位置以及酸的种类（三氟化硼BF3、甲磺酸MeSO3H、三氟甲磺酸CF3SO3H），发生三类酸诱导的跨环反应：迈克尔环化反应（Michael cyclization）、[3+2]环加成反应（[3 + 2] cycloaddition）以及傅-克(ipso)烷基化反应（Friedel−Crafts ipso-alkylation）。当取代基为甲基时，所有受试酸均可通过活化环戊烯酮的羰基基团触发迈克尔环化反应，生成三环二酮类化合物。然而，当取代基为苯基时，三氟化硼与甲磺酸会抑制迈克尔环化反应的进行；而对于三氟甲磺酸，则会根据轮烯酮取代基的位置，分别引发[3+2]环加成反应与傅-克(ipso)烷基化反应。上述三氟甲磺酸参与的反应会发生新颖的重排过程，分别生成2-萘酮（2-naphthalenone）与7-苊烯衍生物（7-acenaphthylene derivatives）。本文从[8]轮烯酮环的受限扭船式构象（constraint twist-boat conformation）以及取代基对分子内环化反应的影响视角，探讨了调控这类跨环环化反应路径的关键因素。此外，本研究发现这类[8]轮烯酮环可轻松发生分子内[2+2]光环化反应（intramolecular [2 + 2] photocyclization），生成四环笼状化合物（tetracyclic cage compounds）；该类化合物在酸的作用下可发生易于进行的逆环化反应（cycloreversion）。