Cecilia Anaya de Parrodi

All Kinds of Reactivity: Recent Breakthroughs in Metal-Catalyzed Alkyne Chemistry

Alkynes of reactions: Recent breakthroughs in metal-catalyzed alkyne reactions, which expand the synthetic utility of alkynes, have been achieved. These approaches broaden the range of alkynes that are accessible by C--N and C--C bond-forming reactions and demonstrate that the use of bifunctional heterobimetallic catalysts can lead to new reactivity and excellent enantioselectivity (see scheme).

Highly diastereoselective alkylation, acylation and aldol condensation of cis- and trans-(N-acyloyl)hexahydrobenzoxazolidin-2-ones

Abstract The potential of hexahydrobenzoxazolidinones 1a – d as chiral auxiliaries was explored. N -Acylation of 1a – d , 2a – d and 3a – d was followed by methylation and benzylation via the corresponding sodium enolates generated by treatment with NaHMDS. Diastereoselectivities of 98% or higher were observed. The absolute configuration of the newly created stereogenic center was established by chemical correlation with 2-benzyl-1-propanol. The stereochemical results are congruent with addition to the electrophile from the less hindered face of a ( Z )-configured enolate, the sodium cation being coordinated by both carbonyl oxygens of the substrate. cis - and trans - N -Propionyl derivatives 2a – d were treated with Bu 2 BOTf/Et 3 N to give dialkylboron enolates 6a – d , which were then reacted with acetaldehyde and benzaldehyde. 1 H and 13 C NMR analyses showed the formation of a single diastereomeric aldol addition product, whose relative configuration was ascertained as syn from the measurement of the 3 J H(2′)/H(3′) coupling constants, and whose absolute configuration was determined by X-ray crystallographic analysis. The results are rationalized in terms of a Zimmerman–Traxler transition state, with a ( Z )-configured enolate where boron is coordinated to the aldehyde carbonyl rather than the oxazolidinone carbonyl. Substrate 2a was also reacted with acyl chlorides via the sodium enolate (NaHMDS). The effect of reaction conditions on O - versus C -acylation, as well as the influence of solvent and additives on diastereoselectivity, are discussed.

Diastereoselective synthesis of 1,2-O-isopropylidene-1,6-dioxaspiro[4,4]nonane applying the methodology of generation of radical cations under non-oxidizing conditions

Abstract We report the stereoselective synthesis of an optically pure spiroketal via an intramolecular tandem hydrogen abstraction reaction promoted by an alkoxy radical. Expanding the use of alkene radical cation under non-oxidizing conditions in the synthetic scenario.

Application of phosphorylated reagents derived from N,N′-di-[(S)-α-phenylethyl]-cyclohexane-1,2-diamines in the determination of the enantiomeric purity of chiral alcohols

Abstract The synthesis of two new N -[( S )-α-phenylethyl] substituted P -chloro-1,3-diazaphospholidines derived from C 2 -symmetric trans -1,2-diaminocyclohexanes, and their application as chiral derivatizing agents in the determination of enantiomeric purities of chiral alcohols by means of 31 P NMR spectroscopy is described.

Preparation of enantiomerically pure cis- and trans-N-(propionyl)hexahydrobenzoxazolidin-2-ones

Abstract A high-yield, five-step synthesis of novel enantiomerically pure cis - and trans - N -(propionyl)-hexahydrobenzoxazolidin-2-ones 5a-d from cyclohexene oxide and ( S )- α -methylbenzylamine is described. The highly diastereoselective benzylation of 5b is also described.

Conformational analysis of cyclic phosphates derived from 5-C′ substituted 1,2-O-isopropylidene-α-d-xylofuranose derivatives

Abstract Twelve 2-phenoxy-2-oxo-1,3,2-dioxaphosphorinanes fused with a 1,2-O-isopropylidene-α- d -xylofuranose moiety in cis orientation and substituted at the C′5 position were prepared in two steps from commercially available diacetone-α- d -glucose. Their conformations, and configurations were determined by 1H and 31P NMR and X-ray crystallographic techniques. Both, chair–twisted–chair and chair–boat equilibria were observed in solution. We observed that the strong anisotropic shielding effect of the benzene ring in the phenoxy group generates an upfield shift of the H1 hydrogen atom, when the cyclic phosphates adopt a boat conformation. This is due to a relative cis-orientation of the P-phenoxy group and the H1 proton of the 1,2-O-isopropylidene-α- d -xylofuranose moiety. Therefore, the configuration of the phosphorus center (SP or RP) can be determined by 1H NMR spectroscopy. Interestingly, the crystal structure of one of the cyclic phosphates exhibits two independent molecules in the asymmetric unit, one with a chair and the other one with a boat conformation.

Novel ring-opening of epoxides and oxetanes with POCl3 or PCl3 in the presence of DMAP

Abstract Efficient synthesis of chlorohydrins by cleavage of oxiranes and oxetanes using POCl 3 or PCl 3 in the presence of DMAP (4- N , N- dimethylaminopyridine) has been studied.

Enantioselective addition of et2zn to benzaldehyde catalyzed by n-(s)-α-methylbenzyl-β-aminoalcohols

Abstract The enantioselective alkylation of benzaldehyde by diethylzine in the presence of catalytic amounts of N-(S)-α-methylbenzyl-β-aminoalcohols as the dilithium salts was studied. The extent of asymmetric induction was found to depend strongly upon the structure of catalyst used and also on the presence of lithium chloride.

Practical Synthesis of Optically Active Alcohols via Asymmetric Transfer Hydrogenation of Aromatic Ketones Using Chiral Rh(III)–Monosulfonamide Ligand Complex in Aqueous Media

A series of monosulfonamide derivatives were synthesized and tested as chiral ligands in the Ru(II),Rh(III)-catalyzed transfer hydrogenation of aromatic ketones in aqueous sodium formate and isopropanol/potassium hydroxide. Possible secondary Cp*methyl-π sulfonamide benzene ring interaction is envisaged and supported by calculations.

o-Nitro­benzoic acid anhydride

The title compound, C14H8N2O7, is a symmetrically substituted acyclic anhydride. The nitro groups are twisted with respect to the benzene rings; these are almost coplanar, with a dihedral angle of 9.07 (9)°.