Intramolecular [1 + 2] and [3 + 2] cycloaddition reactions of cyclopropenone ketals.
J Am Chem Soc
; 132(25): 8527-9, 2010 Jun 30.
Article
em En
| MEDLINE
| ID: mdl-20527885
ABSTRACT
The first intramolecular thermal reactions of cyclopropenone ketals are reported and the work examined substrates tethered to an electron-deficient olefin bearing a single electron-withdrawing substituent. Whereas the intermolecular variants of the reactions provide only the products of an endo-selective [1 + 2] cycloaddition or a carbonyl addition reaction of a thermally generated pi-delocalized singlet vinylcarbene, the intramolecular variants provide either [1 + 2] or [3 + 2] cycloadducts in reactions that depend on the reaction conditions, the alkene-activating substituent, and the nature of the tethering. In addition to providing key mechanistic insights into the thermal [3 + 2] cycloaddition reaction for such substrates, they were also found to proceed under conditions that reflect the ease and regioselectivity of the cyclopropenone ketal cleavage for pi-delocalized singlet vinylcarbene generation. The most effective combination of structural features that impact the reactivity was observed with substrates bearing an aldehyde- or ketone-substituted electron-deficient olefin and incorporating an aryl cyclopropenone ketal substituent built into the linking tether. Simply warming a solution of such substrates in toluene at 80-100 degrees C directly provided the [3 + 2] cycloadducts in excellent yields (60-88%) under mild thermal reaction conditions.
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Base de dados:
MEDLINE
Assunto principal:
Ciclopropanos
Idioma:
En
Ano de publicação:
2010
Tipo de documento:
Article