Novel Diethylaluminum Chloride Promoted Reactions of the Azetidine Ring: Efficient and Stereocontrolled Entry to Functionalized Olefins, Pyrrolidines, and Pyrroles
摘要:
The first examples of Lewis acid promoted fragmentation or rearrangement of the azetidine ring are reported. Azetidine precursors, cis-beta-lactams, were easily available as single cis-diastereoisomers by the Staudinger reaction. Both cis- and trans-4-formyl-beta-lactams react with the appropriate dial or dithiol under acid catalysis to yield dioxolanes or dithiolanes, while reaction with trimethyl orthoformate or benzenethiol gave 4-acetal or thioacetal beta-lactams, respectively. Azetidines were smoothly obtained by reduction of easily available beta-lactams with monochloroalane (AlH2Cl), generated in situ from LiAlH4/AlCl3. The chemical reactivity of azetidines with AlEt2Cl was further investigated. Different substituted azetidines showed varied behavior on product formation during diethylaluminum chloride promoted reactions. Azetidines having 4-methoxyphenyl or 2-furyl groups at C2 and a benzyl or allyl substituent at nitrogen efficiently reacted with AlEt2Cl to give olefins stereoselectively through a fragmentation process, while acetal or thioacetal azetidines under the standard reaction conditions afforded in a stereocontrolled manner pyrrolidines as the sole product. Furthermore, thioacetal azetidines bearing a substituent at C3 on the azetidine ring that can promote aromatization (phenoxy or exocyclic double bond) gave pyrroles by reaction with AlEt2Cl.
Novel Diethylaluminum Chloride Promoted Reactions of the Azetidine Ring: Efficient and Stereocontrolled Entry to Functionalized Olefins, Pyrrolidines, and Pyrroles
摘要:
The first examples of Lewis acid promoted fragmentation or rearrangement of the azetidine ring are reported. Azetidine precursors, cis-beta-lactams, were easily available as single cis-diastereoisomers by the Staudinger reaction. Both cis- and trans-4-formyl-beta-lactams react with the appropriate dial or dithiol under acid catalysis to yield dioxolanes or dithiolanes, while reaction with trimethyl orthoformate or benzenethiol gave 4-acetal or thioacetal beta-lactams, respectively. Azetidines were smoothly obtained by reduction of easily available beta-lactams with monochloroalane (AlH2Cl), generated in situ from LiAlH4/AlCl3. The chemical reactivity of azetidines with AlEt2Cl was further investigated. Different substituted azetidines showed varied behavior on product formation during diethylaluminum chloride promoted reactions. Azetidines having 4-methoxyphenyl or 2-furyl groups at C2 and a benzyl or allyl substituent at nitrogen efficiently reacted with AlEt2Cl to give olefins stereoselectively through a fragmentation process, while acetal or thioacetal azetidines under the standard reaction conditions afforded in a stereocontrolled manner pyrrolidines as the sole product. Furthermore, thioacetal azetidines bearing a substituent at C3 on the azetidine ring that can promote aromatization (phenoxy or exocyclic double bond) gave pyrroles by reaction with AlEt2Cl.
Novel Diethylaluminum Chloride Promoted Reactions of the Azetidine Ring: Efficient and Stereocontrolled Entry to Functionalized Olefins, Pyrrolidines, and Pyrroles
作者:Benito Alcaide、Pedro Almendros、Cristina Aragoncillo、Nati R. Salgado
DOI:10.1021/jo991203c
日期:1999.12.1
The first examples of Lewis acid promoted fragmentation or rearrangement of the azetidine ring are reported. Azetidine precursors, cis-beta-lactams, were easily available as single cis-diastereoisomers by the Staudinger reaction. Both cis- and trans-4-formyl-beta-lactams react with the appropriate dial or dithiol under acid catalysis to yield dioxolanes or dithiolanes, while reaction with trimethyl orthoformate or benzenethiol gave 4-acetal or thioacetal beta-lactams, respectively. Azetidines were smoothly obtained by reduction of easily available beta-lactams with monochloroalane (AlH2Cl), generated in situ from LiAlH4/AlCl3. The chemical reactivity of azetidines with AlEt2Cl was further investigated. Different substituted azetidines showed varied behavior on product formation during diethylaluminum chloride promoted reactions. Azetidines having 4-methoxyphenyl or 2-furyl groups at C2 and a benzyl or allyl substituent at nitrogen efficiently reacted with AlEt2Cl to give olefins stereoselectively through a fragmentation process, while acetal or thioacetal azetidines under the standard reaction conditions afforded in a stereocontrolled manner pyrrolidines as the sole product. Furthermore, thioacetal azetidines bearing a substituent at C3 on the azetidine ring that can promote aromatization (phenoxy or exocyclic double bond) gave pyrroles by reaction with AlEt2Cl.