TY - JOUR
T1 - Stereoselective synthesis of 4,5-diethylidene-oxazolidinones as new dienes in Diels-Alder reactions
AU - Martínez, Rafael
AU - Jiménez-Vázquez, Hugo A.
AU - Reyes, Alicia
AU - Tamariz, Joaquín
PY - 2002
Y1 - 2002
N2 - The N-substituted isomeric (4Z,5Z)- and (4E,5Z)-4,5-diethylideneoxazolidin-2-ones 5 and 6 were synthesized, the latter being favored during the one-step process from the α-diketone 1c and different isocyanates. The steric interaction between the N-substituent and the Me group attached to the exocyclic diene moiety plays a decisive role in controlling the observed stereoselectivity, as suggested by the calculated free energies of the two isomers. Both dienes undergo efficient additions to symmetric dienophiles in thermal Diels-Alder reactions to yield the adducts 11 and 13, respectively. These molecules displayed interesting C-H ···π, and C-H··· X (X = O, Cl) interactions according to their X-ray crystal structures. Isomers 6 suffered highly stereo- and regioselective additions with nonsymmetrical dienophiles such as methyl vinyl ketone or methyl propiolate. Steric interactions, promoted by the inward-pointing Me group in 6, seem to explain such selectivity. These results have also been rationalized by ab initio calculations in terms of the FMO theory.
AB - The N-substituted isomeric (4Z,5Z)- and (4E,5Z)-4,5-diethylideneoxazolidin-2-ones 5 and 6 were synthesized, the latter being favored during the one-step process from the α-diketone 1c and different isocyanates. The steric interaction between the N-substituent and the Me group attached to the exocyclic diene moiety plays a decisive role in controlling the observed stereoselectivity, as suggested by the calculated free energies of the two isomers. Both dienes undergo efficient additions to symmetric dienophiles in thermal Diels-Alder reactions to yield the adducts 11 and 13, respectively. These molecules displayed interesting C-H ···π, and C-H··· X (X = O, Cl) interactions according to their X-ray crystal structures. Isomers 6 suffered highly stereo- and regioselective additions with nonsymmetrical dienophiles such as methyl vinyl ketone or methyl propiolate. Steric interactions, promoted by the inward-pointing Me group in 6, seem to explain such selectivity. These results have also been rationalized by ab initio calculations in terms of the FMO theory.
UR - http://www.scopus.com/inward/record.url?scp=0036122756&partnerID=8YFLogxK
U2 - 10.1002/1522-2675(200202)85:2<464::AID-HLCA464>3.0.CO;2-U
DO - 10.1002/1522-2675(200202)85:2<464::AID-HLCA464>3.0.CO;2-U
M3 - Artículo
SN - 0018-019X
VL - 85
SP - 464
EP - 482
JO - Helvetica Chimica Acta
JF - Helvetica Chimica Acta
IS - 2
ER -