Cis selectivity of salt-free Wittig reactions: a "Leeward Approach" of the aldehyde at the origin?
作者:Manfred Schlosser、Bruno Schaub
DOI:10.1021/ja00385a061
日期:1982.10
to afford, after 2-4 h, the corresponding olefins in 89-99% yield. In each case the trans isomer prevails, cis/trans ratios ranging from 33:67 to 4:96. The remarkable cis-stereoselectivity of Wittigreactions using triphenylphosphonium alkylides is now attributed to a very specific and almost rigid orientation of the Ph groups around the P atom, which sterically hinders approach to the aldehyde in
The stereochemistry of the reactions between tris(2-methoxy-methoxyphenyl)phosphonioethanide (1f), -butanide (2f), and -phenyl-methanide (3f) and a variety of aldehydes was investigated. Ylides having a β-unbranched aliphatic sidechain, such as 2f, and saturated straight-chain aldehydes give olefins with unprecedented cis-selectivity (cis/trans â 200:1).
is driven by a novel activation strategy and features a unique Pd(I)-Pd(I) mechanism, involving an iodide-assisted binuclear step to release the product. This method enables β-selective hydroformylation of a large range of alkenes and alkynes, including sensitive starting materials. Its utility is demonstrated in the synthesis of antiobesity drug Rimonabant and anti-HIV agent PNU-32945. In a broader
Activation Parameters for the Epoxidation of Substitutedcis/trans Pairs of 1,2-Dialkylalkenes by Dimethyldioxirane
作者:Brian S. Crow、W. Rucks Winkeljohn、Angela Navarro-Eisenstein、Elba Michelena-Baez、Paul J. Franklin、Pedro C. Vasquez、Al Baumstark
DOI:10.1002/ejoc.200600427
日期:2006.10
the corresponding cisisomers. The ΔH‡ terms mirrored trends observed in ΔG‡ because ΔS‡ terms for all ten of the compounds were roughly identical. The ΔΔG‡ values, a comparison of the trans to the cisisomer data, yielded positive values of 1.2 to 1.8 kcal/mol for the five sets of data and appeared to be dependent on relative steric interactions. The experimental activationparameter data, consistent
Stereochemistry and regiochemistry of the addition of lodonium nitrate to alkenes
作者:J. William Lown、Alummoottil V. Joshua
DOI:10.1039/p19730002680
日期:——
The stereochemistry of the products was confirmed by relating them chemically with known compounds. Addition to the less hindered (Z)-[β-2H]styrene is also stereospecific, eliminating the possibility of restricted rotation during addition. Ring closure by neighbouring sulphur in the addition of iodonium nitrate to 1-allyl-3,3-diethylthiourea affords a thiazole. The failure to obtain addition and phenyl