Structurally Novel Bi- and Tricyclic β-Lactams via [2 + 2] Cycloaddition or Radical Reactions in 2-Azetidinone-Tethered Enallenes and Allenynes
摘要:
[GRAPHICS]Thermolysis of beta-lactam-tethered enallenyl alcohols gave tricyclic ring structures via a formal [2 + 2] cycloaddition of the alkene with the distal bond of the allene, while the tin-promoted radical cyclization in 2-azetidinone-tethered allenynes proceeded to provide bicyclic beta-lactams containing a medium-sized ring. The access to cyclization precursors was achieved by regio- and stereoselective metal-mediated carbonyl allenylation of 4-oxoazetidine-2-carbaldehydes in an aqueous environment.
Stereoselective Synthesis of 1,2,3-Trisubstituted 1,3-Dienes through Novel [3,3]-Sigmatropic Rearrangements in ?-Allenic Methanesulfonates: Application to the Preparation of Fused Tricyclic Systems by Tandem Rearrangement/Diels?Alder Reaction
Carbonyl Allenylation/Free Radical Cyclization Sequence as a New Regio- and Stereocontrolled Access to Bi- and Tricyclic β-Lactams
作者:Benito Alcaide、Pedro Almendros、Cristina Aragoncillo、María C. Redondo
DOI:10.1021/jo061828s
日期:2007.3.1
A novelapproach to racemic and enantiopure nonconventional fused bi- and tricyclic β-lactams has been developed by using regio- and stereocontrolled intramolecular free radical reactions in monocyclic 2-azetidinone-tethered allenynes and haloallenes. The access to allene cyclization precursors was achieved by metal-mediated carbonyl allenylation of appropriately substituted 4-oxoazetidine-2-carbaldehydes
Reactions of racemic as well as optically pure carbonyl-β-lactams with stabilized organo-indium reagents were investigated in aqueous media. The regio- and stereochemistry of the processes were generally good, offering a convenient asymmetric entry to densely functionalized hydroxy-β-lactams.
Metal-mediated carbonyl allenylation and propargylation of 4-oxoazetidine-2-carbaldehydes were investigated in aqueous environment. Different propargyl bromide and metal promoters showed varied regio- and stereoselectivities on product formation. In addition, an unprecedented one-pot stereoselective synthesis of beta-chlorinated allylic alcohols, which can also be considered as functionalized allylsilanes
[GRAPHICS]Thermolysis of beta-lactam-tethered enallenyl alcohols gave tricyclic ring structures via a formal [2 + 2] cycloaddition of the alkene with the distal bond of the allene, while the tin-promoted radical cyclization in 2-azetidinone-tethered allenynes proceeded to provide bicyclic beta-lactams containing a medium-sized ring. The access to cyclization precursors was achieved by regio- and stereoselective metal-mediated carbonyl allenylation of 4-oxoazetidine-2-carbaldehydes in an aqueous environment.