Photoaddition of Alkenes to Conjugated α-Diketones: Tandem
Cyclizations Leading to Tetrasubstituted Furans<sup>1a</sup>
Ashis K. Mukherjee
Paul Margaretha
William C. Agosta
10.1021/jo952079+.s001
https://acs.figshare.com/articles/journal_contribution/Photoaddition_of_Alkenes_to_Conjugated_-Diketones_Tandem_Cyclizations_Leading_to_Tetrasubstituted_Furans_sup_1a_sup_/3701679
Photocycloaddition of <b>9a</b>−<b>c</b> with
<b>2</b> leads cleanly to tetrasubstituted furans
<b>12a</b>−<b>c</b>, respectively, in
yields of ∼85%. The reactive triplet is efficiently sensitized
by 2-benzoylnaphthalene and quenched
by anthracene, indicating that <i>E</i><sub>T</sub> is in the
range 43−58 kcal/mol. A mechanism is proposed
involving an alkyl propargyl biradical (as <b>10</b>) that closes
first to a vinyl carbene (as <b>11</b>) and then
to product. Reaction of <b>9c</b> with <b>20</b> furnishes
only <b>22</b>, and this result rules out an
alternative
mechanism in which the order of steps leading to the carbene is
reversed.
1996-05-17 00:00:00
9 c
Cyclization
Diketone
E T
Photocycloaddition
Alkene
alternative mechanism
Tetrasubstituted Furans 1
reactive triplet
vinyl carbene
alkyl propargyl biradical
Photoaddition
quenched
anthracene
result rules
yield
kcal
tetrasubstituted furans 12
Conjugated
benzoylnaphthalene
Tandem