Acyclic C-nucleosides: Synthesis of chiral 1,1-diheteroaryl-alditols and X-ray crystal structure of 2,3,5-tri-O-benzyl-1,1-di-(2'-pyrryl)-1-deoxyl-D-arabinitol

Tetra-O-acetyl-D-ribose, penta-O-acetyl-D-glucose, 2,3;5,6-di-O-isopropylidene-D-mannofuranose, 2,3,5-tri-O-benzyl-D-arabinofuranose and 2,3,5,6-tetra-O-benzyl-D-glucose react with pyrrole and indole, in presence of Lewis acids, to afford C-glycosylpyrroles and indoles in position 2 and 3 respectively (acyclic C-nucleosides, 1-7). The crystal structure of 4 was determined by X-ray crystallography

Stereoselective synthesis of 2-acyl-3,4-dihydro-1,4-benzothiazines

2-Benzylidene-4-methyl-3-oxo-2H-1,4-benzothiazine 2 undergoes 1,2-addition with MeMgI and allylic magnesium halides to give 2-acyl-4-methyl-3-phenyl-3,4-dihydro-2H-1,4-benzothiazines 3a-d. Lithiation of 3a and subsequent reaction with MeI and PhCH2Br leads to compounds 3e, 3f, 3h and 3i. In contrast, the reaction of lithiated 3a with benzaldehyde and 2,6-dichlorobenzaldehyde furnished compounds 3k and 3l respectively. © 1994

Homochiral α,β-unsaturated γ-lactams: Versatile templates

The enantiomerically pure crystalline α,β-unsaturated γ-lactams 4 and 5 have been synthesized by utilizing 2,3-O-isopropylidene-D-glyceraldehyde (3) as chiral source and novel N-tert-butoxycarbonyl-2-(tert-butyldimethylsiloxy)pyrrole (TBSOP) as four carbon homologative reagent. Unsaturated lactam 4 has been selectively elaborated into hydroxylated pyrrolidinones 7, 8, and 11 by stereocontrolled procedures involving conjugate addition of organocuprates, cis-dihydroxylation, and α-alkylation via hydrogenation and enulate formation. The absolute stereochemistries of 4 and 5 have been secured by single crystal X-ray analyses. © 1992

Transition-metal complexes of cyclohexane-1,2-dione bis(thiosemicarbazone) (H2L). Crystal structures of [ZnL(OH2)]·dmf (dmf = dimethylformamide) and [Zn(H2L)Cl]Cl·2H2O

The reaction of chlorides and acetates of FeII, NiII, CuII and ZnII with the polydentate ligand cyclohexane-1,2-dione bis(thiosemicarbazone) (H2L) led to the formation of some novel complexes which have been characterized by spectroscopic methods (NMR, IR). The crystal structures of the two compounds [ZnL(OH2)]·dmf (dmf = dimethylformamide) 1 and [Zn(H2L)Cl]Cl·2H2O 2 have been determined. In both complexes the co-ordination geometry about zinc is distorted square-planar pyramidal. The axial sites are occupied by a water molecule in 1 or by a chlorine atom in 2. The ligand is dideprotonated in 1 and neutral in 2, so that in 1 a higher π-delocalization is observed

Total synthesis of 1,5-dideoxy-1,5-iminoalditols

Enantiomerically pure 1,5-dideoxy-1,5-imino-D-glycero-D-allo-heptitol (10) has been synthesized in ca. 9% overall yield by utilizing 2,3-O-isopropylidene-D-glyceraldehyde-N-benzylimine (1) as a chiral source and 2-(trimethylsiloxy)furan (2) as a homologative reactant. The opening move was the preparation of properly protected seven-carbon butenolide 4, followed by diastereoselective anti, cis-dihydroxylation of the lactone double bond and furanose-to-azapyranose ring expansion. This generated a piperidine intermediate 7, the stereochemistry of which was secured by a single crystal X-ray analysis of its diacetate 9. © 1992

Selective reactions using N-(tert-butoxycarbonyl)-2-(tert-butyldimethylsiloxy)pyrrole: concise asymmetric syntheses of (+)-1-deoxy-8-epi-castanospermine and its enantiomer

Advantage being taken of the versatility of the siloxydiene TBSOP in asymmetric synthesis, (6S,7R,8S,8aR)-6,7,8-trihydroxyindolizidine 11 has been assembled from the L-threose derivative 1 in six or eight steps in 22-30% overall yield. Pivotal to the success of this total synthesis venture is the ready availability of unsaturated lactam 2 with complete stereocontrol. As a corollary, the synthesis of the known indolizidine enantiomer ent-11 confirms the feasibility of the procedure. The structure of compound 5 has been determined by X-ray crystallography