Photocycloaddition of N-Acyl Enamines to Aldehydes and Its Application to the Synthesis of Diastereomerically Pure 1,2-Amino Alcohols
摘要:
The regio- and stereoselective synthesis of the protected cis-3-aminooxetanes cis-5 and cis-7 is reported. The oxetanes were obtained by the photocycloaddition of aliphatic (6c-e) and aromatic (4, 6a) aldehydes to the corresponding enamides (1a-d,h) or enecarbamates (le-g). The enamine derivatives used in the Paterno-Buchi reaction were either commercially available or prepared from the corresponding acetaldehyde imines 2 by acylation. The oxetane formation proceeded with good-to-excellent simple diastereoselectivity for aromatic aldehydes (56-82% yield) and moderate selectivity for aliphatic aldehydes (46-55% yield). The cis-3-aminooxetanes are precursors for syn- and anti-1,2-amino alcohols. The relative configuration established in the photochemical step was retained upon nucleophilic ring opening between the oxygen atom and carbon atom C-4. By this means, syn-1,2-amino alcohols such as 8 and 10 were available in good yields. In contrast, the N-Boc-protected cis-3-aminooxetanes cis-5e and cis-5f were transformed into anti-1,2-amino alcohols. Upon treatment with trifluoroacetic acid, they underwent an intramolecular nucleophilic substitution at the carbon atom C-2 of the oxetane and the oxazolidinones II and 12 were formed. Because the substitution occurs with inversion of configuration, anti-1,2-amino alcohols, e.g., ephedrine (15), are accessible.
Photocycloaddition of N-Acyl Enamines to Aldehydes and Its Application to the Synthesis of Diastereomerically Pure 1,2-Amino Alcohols
摘要:
The regio- and stereoselective synthesis of the protected cis-3-aminooxetanes cis-5 and cis-7 is reported. The oxetanes were obtained by the photocycloaddition of aliphatic (6c-e) and aromatic (4, 6a) aldehydes to the corresponding enamides (1a-d,h) or enecarbamates (le-g). The enamine derivatives used in the Paterno-Buchi reaction were either commercially available or prepared from the corresponding acetaldehyde imines 2 by acylation. The oxetane formation proceeded with good-to-excellent simple diastereoselectivity for aromatic aldehydes (56-82% yield) and moderate selectivity for aliphatic aldehydes (46-55% yield). The cis-3-aminooxetanes are precursors for syn- and anti-1,2-amino alcohols. The relative configuration established in the photochemical step was retained upon nucleophilic ring opening between the oxygen atom and carbon atom C-4. By this means, syn-1,2-amino alcohols such as 8 and 10 were available in good yields. In contrast, the N-Boc-protected cis-3-aminooxetanes cis-5e and cis-5f were transformed into anti-1,2-amino alcohols. Upon treatment with trifluoroacetic acid, they underwent an intramolecular nucleophilic substitution at the carbon atom C-2 of the oxetane and the oxazolidinones II and 12 were formed. Because the substitution occurs with inversion of configuration, anti-1,2-amino alcohols, e.g., ephedrine (15), are accessible.
aromatic aldehydes and silyl enol ethers in benzene as the solvent. The reactions occur with high simple diastereoselectivity and, when R¹ is chiral, with high facial diastereoselectivity. Under similar conditions, but in acetonitrile rather than benzene as the preferred solvent, the Paternò-Büchi reaction of N-acylenamines (enamides) gives the corresponding protected 3-aminooxetanes. The cis-products
Photocycloaddition of <i>N</i>-Acyl Enamines to Aldehydes and Its Application to the Synthesis of Diastereomerically Pure 1,2-Amino Alcohols
作者:Thorsten Bach、Jürgen Schröder
DOI:10.1021/jo9819988
日期:1999.2.1
The regio- and stereoselective synthesis of the protected cis-3-aminooxetanes cis-5 and cis-7 is reported. The oxetanes were obtained by the photocycloaddition of aliphatic (6c-e) and aromatic (4, 6a) aldehydes to the corresponding enamides (1a-d,h) or enecarbamates (le-g). The enamine derivatives used in the Paterno-Buchi reaction were either commercially available or prepared from the corresponding acetaldehyde imines 2 by acylation. The oxetane formation proceeded with good-to-excellent simple diastereoselectivity for aromatic aldehydes (56-82% yield) and moderate selectivity for aliphatic aldehydes (46-55% yield). The cis-3-aminooxetanes are precursors for syn- and anti-1,2-amino alcohols. The relative configuration established in the photochemical step was retained upon nucleophilic ring opening between the oxygen atom and carbon atom C-4. By this means, syn-1,2-amino alcohols such as 8 and 10 were available in good yields. In contrast, the N-Boc-protected cis-3-aminooxetanes cis-5e and cis-5f were transformed into anti-1,2-amino alcohols. Upon treatment with trifluoroacetic acid, they underwent an intramolecular nucleophilic substitution at the carbon atom C-2 of the oxetane and the oxazolidinones II and 12 were formed. Because the substitution occurs with inversion of configuration, anti-1,2-amino alcohols, e.g., ephedrine (15), are accessible.