10.1021/ja01617a041
The study investigates the preparation and hydrolysis of acetals derived from various alcohols, including methylvinylcarbinol, phenylvinylcarbinol, and (±)-α-phenylethyl alcohol. The acetals were synthesized using acetaldehyde and the respective alcohols in the presence of calcium chloride and hydrogen chloride as a catalyst. The hydrolysis of these acetals was examined to determine the reaction pathways and intermediates involved. For instance, the hydrolysis of methylvinylcarbinyl acetal yielded methylvinylcarbinol without allylic rearrangement, indicating that the normal hydrolysis path was preferred over an abnormal cleavage process. Similarly, the hydrolysis of (±)-α-phenylethyl alcohol acetal resulted in the recovery of the original alcohol with complete retention of configuration, suggesting that no carbonium ion intermediates were formed. The study also explored the hydrolysis of phenylvinylcarbinyl acetal, which produced phenylvinylcarbinol and subsequently cinnamyl alcohol through isomerization, further supporting the conclusion that the normal hydrolysis mechanism was predominant. Additionally, the study delved into the stereochemistry of rearrangement involving migration between multiply-bonded carbons, using compounds like cis- and trans-1-p-bromophenyl-1-phenyl-2-bromoethylene-1-14C and converting them to labeled 4-bromotolans, analyzing the migration percentages of different groups during the rearrangement process.
10.1021/jo0011437
The research focuses on the first total synthesis of the natural product (-)-heliannuol E, a heliannane-type sesquiterpenoid with significant biological activity, isolated from Helianthus annuus L. cv. SH-222. The study outlines a strategic synthetic route involving various chemical reactions and techniques, such as Sonogashira coupling, lipase-mediated desymmetrization, oxidation, Wittig olefination, and reductive deacetylation. Key reactants include 3-arylpropargyl alcohol, which is reduced to a cinnamyl alcohol, and further transformed through a series of reactions to construct the complex molecule. The synthesis strategy involves selective dehydration, cyclization, and chemoenzymatic desymmetrization to achieve the desired stereochemistry at two stereogenic centers. The researchers used spectral studies (1H-1H COSY, 1H-13C HETCOR, NOE) for structural elucidation and HPLC on a Chiralcel OD column to determine the enantiomeric excess (ee) of the synthesized compounds. The successful synthesis was confirmed by comparing the spectral data (1H and 13C NMR, IR, and mass spectral data) and optical rotation of the synthesized product with those of the natural product.
Xn
