Preparation of Chiral Hydroxy Carbonyl Compounds and Diols by Ozonolysis of Olefinic Isoborneol and Fenchol Derivatives: Characterization of Stable Ozonides by1H-,13C-, and17O-NMR and Electrospray Ionization Mass Spectrometry
摘要:
The allylic and homoallylic alcohols 1-8, prepared from (+)-camphor and (-)-fenchone, were ozonized in Et2O at -78 and treated with Et3N or LiAlH4 to give the chiral hydroxy carbonyl compounds 9-16 and the diols 17-24, respectively (Scheme I). In the case of the diols 19 and WI the formation of new chiral centers proceeded with high diastereoselectivity. These diols were prepared highly diastereoselectively also by LiAlH4 reduction of the hydroxy carbonyl compounds 11 and 16a, respectively (Scheme 2). The absolute configuration of the new chiral centers in 19 and 24 was determined by X-ray and NMR methods. The ozonization of compounds 2, 3, 7, and 8 provided the relatively stable hydroxy-substituted 1,2,4-trioxolane derivatives (ozonides) 37-40 (Scheme 5) which were characterized by H-1- and C-13-NMR spectra. ESI-MS, and natural-abundance O-17-NMR spectra.
An Unusual Approach to the Synthesis of Enantiomerically Cis Linear Homoallylic Alcohols Based on the Steric Interaction Mechanism of Camphor Scaffold
摘要:
Camphor is used as the chiral auxiliary for the enantioselective synthesis of cis linear homoallylic alcohols. A range of catalysts, aldehydes, and solvents were investigated to obtain the optimum yield, enantioselectivity, and cis olefinic geometry.
Synthesis and absolute configuration of new chiral epoxyalcohols by stereoselective epoxidation of allylic and homoallylic alcohols with a (1R)-(+)-camphor skeleton
100% diastereoselectively to 10. The epoxyalcohol 10 underwent a stereoselective intramolecular cyclisation during the epoxydation with rearrangement of the camphor skeleton to the oxatricyclo derivative 11. The absoluteconfigurations of the new chiral compounds were determined by NMR methods.
The new chiral nonracemic homoallylic exo-alcohols 6, 7, 10 with (1R)-(+)-camphor (1) and endo-alcohols 8, 9, 11 with (1R)-(−)-fenchone (2) skeleton were synthesized in high yields by the stereoselective addition of allyl and substituted allylic Grignard reagents 3–5 to 1 and 2, respectively. The addition of the 2-butenyl (crotyl) reagent 5 occurred with high selectivity leading exclusively to α-methylallyl