[1,3]-oxygen to carbon rearrangement for the construction of carbon-carbon bonds between adjacent rings and 1,3-dioxepines in synthesis
Date
2007
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Abstract
Several methods for the stereoselective formation of carbon-carbon bonds between contiguous rings where a stereogenic center is already present have been examined. The approaches investigated were: a [1,3]-oxygen to carbon rearrangement of cyclic vinyl acetals; an intermolecular enolsilane addition into an in situ generated oxocarbenium ion; an intramolecular conjugate addition of tethered alkoxy enones; and epimerization of several α-pyranyl cycloalkanones. These routes have been found to be complementary in several cases and have enabled formation of both the traps: anti and cis:anti stereoisomers in good to excellent yields and varying diastereoselectivities. The C2-C2' relative stereochemistry of the carbon-carbon bond between the adjacent rings was proven via a chemical correlation. The versatility of 1,3-dioxepines as precursors to the formation of 1,4-diols and 1,2,4-triols has been examined. The rapid synthesis of unsymmetrical 1,3-dioxepines and the installation of a 4-acetoxy substituent as a synthetic handle for further functionalization has been realized. The Lewis acid mediated addition into in situ generated oxocarbenium ions has been developed for variety of different nucleophiles. Furthermore, a highly trans -diastereoselective Heck reaction has been performed on unsymmetrical 1,3-dioxepines and their synthetic utility as precursors to the formation of 2,3,4-alkyl substituted tetrahydrofurans and 2-methoxy-4,5-alkyl substituted tetrahydrofurans have been exploited.
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Subject
adjacent rings
carbon-carbon bonds
oxygen to carbon rearrangement
organic chemistry