Intermolecular cycloaddition of N-boranonitrone with alkenes.
Ethyl glyoxylate O-tert-butyldimethylsilyloxime (8), on treatment with 2.2 equiv of BF3 x OEt2, generated N-boranonitrone E, which underwent intermolecular cycloaddition with alkenes 18 to afford isoxazolidines 19 in moderate to high yields. The cycloaddition of N-boranonitrone E with most of the alkenes gave 3,5-trans isoxazolidines as the major isomers via a concerted mechanism. However, in the case of 1-methylated cyclic alkenes (18j and 18l), the cycloaddition surprisingly furnished the 3,3a-cis-cycloadducts (19j and 19l) as major isomers. A possible explanation is that the reaction of 1-methylated cyclic alkenes proceeds mainly via a stepwise mechanism. This reaction of terminal alkenes is very useful for synthesis of 1,3-anti aminoalcohol derivatives by reductive cleavage of an N-O bond.
Morita
Nobuyoshi
N
Showa Pharmaceutical University, Higashi-tamagawagakuen, Machida, Tokyo 194-8543, Japan.
Fukui
Kenji
K
Irikuchi
Jinshi
J
Sato
Hiroshi
H
Takano
Yuu
Y
Okamoto
Iwao
I
Ishibashi
Hiroyuki
H
Tamura
Osamu
O
D000475:Alkenes / Q000737:chemistry*; D000605:Amino Alcohols / Q000138:chemical synthesis; D001880:Boranes / Q000138:chemical synthesis / Q000737:chemistry*; D003500:Cyclization; D007555:Isoxazoles / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D009589:Nitrogen Oxides / Q000138:chemical synthesis / Q000737:chemistry*; D013237:Stereoisomerism
D000475:Alkenes; D000605:Amino Alcohols; D001880:Boranes; D007555:Isoxazoles; D009589:Nitrogen Oxides; C015388:nitrones