%0 Journal Article
%A Barluenga, José
%A Ballesteros, Alfredo
%A Bernardo de la Rúa, Ramón
%A Santamaría, Javier
%A Rubio, Eduardo
%A Tomás, Miguel
%D 2003
%T Group 6 Heteroatom- and Non-Heteroatom-Stabilized Carbene
Complexes. β,β‘- and α,β,β‘-Annulation Reactions of Cyclic
Enamines
%U https://acs.figshare.com/articles/journal_contribution/Group_6_Heteroatom-_and_Non-Heteroatom-Stabilized_Carbene_Complexes__-_and__-Annulation_Reactions_of_Cyclic_Enamines/3645585
%R 10.1021/ja0278077.s001
%2 https://acs.figshare.com/ndownloader/files/5734434
%K cycloheptanones 15
%K semibullvalenes 5
%K methoxy group
%K chemical behavior
%K 4 b
%K THF
%K bicyclo
%K enantioenriched
%K annulation
%K endo
%K cyclohexanone enamines
%K Enamine 3
%K Cyclic Enamines Cyclization reactions
%K compounds 7
%K metalate intermediates 6
%K group 6 Heteroatom
%K 13 C NMR
%K Fischer carbene complexes 16
%K alkenylcarbene complexes 1
%K enamines 3
%K exo
%K room temperature
%K group 6 Fischer carbene complexes
%K carbene complexes 2
%X Cyclization reactions of group 6 Fischer carbene complexes with cyclopentanone and cyclohexanone enamines are described. Enamine 3a undergoes thermal α,β,β‘-annulation with alkenylcarbene
complexes 1 and 2 (THF, 60 °C), affording semibullvalenes 5. The metalate intermediates 6, resulting
from β,β‘-annulation of the enamines 3a and 4a, were quantitatively formed by running the reaction in
hexane at room temperature. Acid-promoted demetalation of 6 afforded endo-2-bicyclo[3.2.1]octen-8-ones
7 and endo/exo-2-bicyclo[3.3.1]nonen-9-ones 8 (endo/exo = 5:1). Using (S)-methoxymethylpyrrolidine-derived enamines 3b and 4b,c allowed highly enantioenriched cycloadducts endo-(+)-7 as well as endo-(−)-8 and exo-(−)-8 to be accessed. The non-heteroatom-stabilized carbene complex 10 was formed from
complex 6 by Me3SiOTf-promoted elimination of the methoxy group, characterized by 13C NMR, and
transformed into the organic compounds 7, 7-d, and 11 as well as into bicyclo[3.2.1]octan-2,8-diones 14
and cycloheptanones 15. On the basis of this sequence, enantioenriched cycloheptanones (+)-15 were
efficiently prepared in one pot from carbene complexes 2 and enamine 3b (51−55% yield, 91−96% ee).
Extension of this work to simple Fischer carbene complexes 16 allowed an appropriate way to generate
the nonstabilized pentacarbonyl[(phenyl(alkyl)carbene]tungsten complex 17 to be designed, for which the
thermal and chemical behavior leading to compounds 18−21 is described.
%I ACS Publications