The influence of protective groups on diastereofacial selectivity of Diels-Alder cycloaddition reactions.
The diastereofacial selectivity of both inter- and intramolecular Diels-Alder reactions with dienes having an allylic stereogenic center has been studied by varying the allylic oxygen protective group. Four different hydroxy protective groups were investigated including benzyl, t-butyldiphenylsilyl, triethylsilyl, and t-butyldimethylsilyl ethers. For inter-molecular reactions, the benzyl ether derivative gave the highest pi-facial selectivity through a transition state in which the allylic stereocenter favors the CH eclipsed conformation. For intramolecular cycloadditions, the t-butyldimethylsilyl group gave a slightly higher selectivity than the benzyl ether derivative through a transition state in which the allylic stereocenter favors the CO eclipsed conformation. The opposite diastereofacial selectivity observed for inter- and intramolecular reactions is explained by considering both steric and electronic effects.
Gung
B W
BW
Department of Chemistry, Miami University, Oxford, OH 45056, USA.
Mareska
D A
DA
Karipidis
A
A
Henry
T
T
D002625:Chemistry, Organic; D004987:Ethers / Q000737:chemistry; D006838:Hydrocarbons / Q000138:chemical synthesis / Q000737:chemistry; D008956:Models, Chemical; D008968:Molecular Conformation; D015394:Molecular Structure; D055601:Organic Chemistry Phenomena; D013237:Stereoisomerism
D004987:Ethers; D006838:Hydrocarbons