Stereoselective migration of sterically hindered organoboranes in cyclic and acyclic systems. A stereoselective allylic C-H activation reaction

The thermal migration of cyclic and acyclic organoboranes were studied. In most cases, a stereoselective 1,2-dyotropic migration was observed, allowing the stereocontrol of three contiguous chiral centers. Scope and limitations of this thermal migration are presented.     

Synthesis of 3β,20S-dihydroxydammar-24-en-12-one 3,20-di-O-β-D-glucopyranoside (chikusetsusaponin-LT8), a glycoside from Panax japonicus

A method for preparative production of 3β,20S-dihydroxydammar-24-en-12-one 3,20-di-O-β-D-glucopyranoside (1), a glycoside from Panax japonicus, chikusetsusaponin-LT₈ was developed. Chemical transformation of betulafolientriol, a component of Betula leaves extract, produced the 12-keto-20S-protopanaxadiol (3β,20S-dihydroxydammar-24-en-12-one) (2), exhaustive glycosylation of which by 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosylbromide (3) under Koenigs—Knorr reaction conditions with subsequent removal of protecting groups formed 3β,20S-dihydroxydammar-24-en-12-one 3,20-di-O-β-D-glucopyranoside (1). The principal glycosylation product was 3β,20S-dihydroxydammar-24-en-12-one 3-O-β-D-glucopyranoside if equimolar amounts of (2) and (3) were used. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 44–48, January–February, 2006.     

Use of1H and13C NMR spectroscopy to determine the stereochemistry of 1 - methyl- δ4-octalin- 1,2-dicarboxylic acids and their derivatives

Conclusions The combined use of the¹H and¹³C NMR spectra makes it possible to unequivocally assign 1-methyl-⁴-octalin-l,2-dicarboxylic acids and their derivatives to the proper steric series.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1429–1431, June, 1977.     

3β-Methoxyolean-18-ene (miliacin) from the marine fungus Chaetomium olivaceum

A pentacyclic tritepenoid, 3-methoxyolean-18-ene (miliacin), was isolated for the first time from the marine fungus Chaetomium olivaceum. Its structure was determined on the basis of 2D NMR spectroscopy and X-ray diffraction data.     

Asymmetric nitrogen—41: Stereochemistry of bicyclic 1,2-cis-diaziridines

The twisting of 5- and 6-membered rings in bicyclic cis-diaziridines—1,5-diazabicyclo [3.1.0]hexanes 12–17 and l,6-diazabicyclo[4.1.0]heptane 18—is a rapid process in the time scale of ¹H- and ¹³C-NMR even at -80°. According to the ¹H- and ¹³C-NMR spectra, 1,5-diazabicyclo [3.1.0]hexanes 12,13,15a,15b and 16a,16b do, exist mostly in the boat form ; only the introduction of endo substituents into position 3 or 6 leads to the population of the chair, as is the case with 14 and 17. 2,4-Dialkyl substituted 1,5-diaza- and 1,3,5-triazabicyclo[3.1.0]hexanes are formed via a transition cyclization state similar in its geometry to the initial chair-shaped N-chlorodi(tri)azanes.