TY - JOUR
T1 - High Stereoselectivity and Facial Selectivity in Diels-Alder Cycloadditions of Novel Captodative Olefins
T2 - α-Alkoxyvinyl(ethoxy)carbene Chromium Complexes with Cyclopentadienes
AU - Vázquez, Miguel A.
AU - Cessa, Liliana
AU - Vega, José Luis
AU - Miranda, René
AU - Herrera, Rafael
AU - Jiménez-Vázquez, Hugo A.
AU - Tamariz, Joaquín
AU - Delgado, Francisco
PY - 2004/4/12
Y1 - 2004/4/12
N2 - A study of reactivity and selectivity of the new Fischer carbene complexes (CO) 5Cr=C[C(=CHR′)(OR)]OCH 2CH 3 (3, R′ = H, R = CH 2CH 3; 4, R′ = H, R = CH 2CH 2CH 3; 5, R′ = H, R = CH 2CH 2CH 2CH 3; 6, R′ = CH 3 (E and Z), R = CH 2CH 3) was carried out in Diels-Alder cycloadditions with cyclopentadiene (1) and 1,2,3,4,5- pentamethylcyclopentadiene (7). The cycloadditions between the α-alkoxyvinyl(ethoxy)carbene complexes 3, 4, and 5 with 1 were found to be highly stereoselective, favoring the endo adduct at a much higher level than that observed for the analogous α-alkoxy-α,β-unsaturated esters, whereas complex 6E showed low reactivity. When 1,2,3,4,5- pentamethylcyclopentadiene (7) was employed, the cycloadditions with α-alkoxyvinyl(ethoxy)carbene complexes 3-6E were highly anti/exo selective. The exo adducts form new alkoxy-chelated tetracarbonyl carbene complexes. The stereo-chemical assignment of the cycloadducts was supported by NOE measurements, and the chelated exo cycloadduct 21 was further characterized by single-crystal X-ray diffraction.
AB - A study of reactivity and selectivity of the new Fischer carbene complexes (CO) 5Cr=C[C(=CHR′)(OR)]OCH 2CH 3 (3, R′ = H, R = CH 2CH 3; 4, R′ = H, R = CH 2CH 2CH 3; 5, R′ = H, R = CH 2CH 2CH 2CH 3; 6, R′ = CH 3 (E and Z), R = CH 2CH 3) was carried out in Diels-Alder cycloadditions with cyclopentadiene (1) and 1,2,3,4,5- pentamethylcyclopentadiene (7). The cycloadditions between the α-alkoxyvinyl(ethoxy)carbene complexes 3, 4, and 5 with 1 were found to be highly stereoselective, favoring the endo adduct at a much higher level than that observed for the analogous α-alkoxy-α,β-unsaturated esters, whereas complex 6E showed low reactivity. When 1,2,3,4,5- pentamethylcyclopentadiene (7) was employed, the cycloadditions with α-alkoxyvinyl(ethoxy)carbene complexes 3-6E were highly anti/exo selective. The exo adducts form new alkoxy-chelated tetracarbonyl carbene complexes. The stereo-chemical assignment of the cycloadducts was supported by NOE measurements, and the chelated exo cycloadduct 21 was further characterized by single-crystal X-ray diffraction.
UR - http://www.scopus.com/inward/record.url?scp=2342429394&partnerID=8YFLogxK
U2 - 10.1021/om0343317
DO - 10.1021/om0343317
M3 - Artículo
SN - 0276-7333
VL - 23
SP - 1918
EP - 1927
JO - Organometallics
JF - Organometallics
IS - 8
ER -