Pablo L. Bernad

Samarium-Mediated beta-Elimination in Dihalo Alcohols: Diastereoselective Synthesis of (Z)-Vinyl Halides.

High diastereoselectivity in beta-elimination reactions of O-acetyl 1,1-dihaloalkan-2-ols to give (Z)-vinyl halides was achieved by using samarium diiodide [Eq. (1)]. The reaction was also highly diastereoselective and totally chemoselective when a mixture of diastereoisomers was used as substrate (X(1), X(2)=halogen; X(1) not equal X(2)).

Addition Reactions of Chloro- or Iodomethyllithium to Imines. Synthesis of Enantiopure Aziridines and β-Chloroamines

We report a novel, simple, and efficient synthesis of aziridines and 1-chloroalkan-2-amines by the reaction of imines derived from various aldehydes and p-toluenesulfonamide or benzenesulfonamide with iodo- or chloromethyllithium, respectively. Both halogenated anions were generated in situ by treatment of diiodo- or chloroiodomethane with methyllithium at -78 or 0 degrees C. The reaction of in situ generated iodo- or chloromethyllithium could also be performed from chiral 2-aminoaldimines to yield enantiopure aziridines or (2S,3S)-2,3-diamino-1-chloroalkanes with high stereoselectivity.

Samarium diiodide-promoted diiodomethylation of carbonyl compounds with iodoform. Synthetic applications of diiodoalcohols

Abstract A rapid and effective diiodomethylation of carbonyl compounds using SmI 2 and iodoform is described. Transformations of the obtained diiodoalcohols 2 into α-iodoaldehydes 5 and α-hydroxyacids 6 is also reported.

Synthesis of Isotopically Labeled (E)‐β,γ‐Unsaturated Esters with Total or High Diastereoselectivity by Using Samarium Diiodide

A simple, efficient, highly diastereoselective method for preparing (E)-α,δ-dideuterio-β,γ-unsaturated esters: SmI2 -promoted reduction/elimination of α-halo-β-hydroxy-γ,δ-unsaturated esters in the presence of D2 O. This provides the desired products in which the C-C double bond is generated with total or high diastereoselectivity.

Nucleophilic ring closure and opening of aminoiodohydrins

Abstract Enantiopure aminoiodohydrins obtained from α-aminoaldehydes and Sm/CH 2 I 2 have been transformed into regioisomeric aminoiodohydrins, aminoepoxides, azetidines or 1,3-oxazolidines. The key step in these transformations is a nucleophilic opening–closing process.

Endogenous Hormonal Profiles in Hop Development

Changes in gibberellins (GAs), indole-3-acetic acid (IAA), and cytokinins associated with the transition from vegetative growth to reproductive growth in Humulus lupulus L. buds and leaves harvested at fortnight intervals were studied. During vegetative growth, GA1 increased gradually and the lowest content was observed during flower development. Both GA3 and GA4 showed a dramatic increase in the samples taken from the apical part of axillary branches from plants 4–5 m high, which corresponds to the maximum vegetative development prior to macroscopically visible inflorescences. Notable increases in the cytokinins trans-zeatin (t-Z), isopentenyladenine (iP), and the riboside and ribotide forms of iP were also obtained. The auxin, indole-3-acetic acid, was the most abundant plant hormone, and its content was highest during vegetative growth. These results show for the first time a relationship between endogenous hormone profiles and both vegetative and reproductive development in hop plants, which may be relevant for future research on the control of the flowering by exogenous hormone applications.

Preparation of disubstituted epichlorohydrins with total diastereoselectivity. Transformation of α-bromocarbonyl compounds into allyl alcohols

Abstract Epichlorohydrins 3 have been obtained with total diastereoselectivity from α-bromocarbonyl compounds and chloromethyllithium generated in situ. The treatment of compounds 3 with lithium iodide or lithium powder affords allyl alcohols 4 in a regioselective manner.

A simple and efficient transformation of Fischer carbene complexes into bromomethyl ketones or β-ketoesters

Abstract Fischer-type carbene complexes react via nucleophilic attack with dibromomethyllithium or haloester lithium enolates to afford bromomethyl ketones or β-ketoesters, respectively.

TOTAL DIASTEREOSELECTIVE SYNTHESIS OF CHROMIUM CYCLOPROPYLCARBENE COMPLEXES

Abstract Trans -substituted chromium cyclopropylmethoxycarbene complexes 4 have been obtained with total diastereoselectivity through a conjugated addition of in situ generated chloromethyllithium to vinylmethoxycarbene chromium complexes.

Efficiency of extrography in the fractionation of coal-derived oils☆

Abstract Two coal-derived oils consisting of compounds easily identified by gas chromatography-mass spectrometry (g.c.-m.s.) were fractionated into compound classes by extrography with the aim of investigating the applicability and reliability of this technique for the fractionation of complex mixtures into compound classes. Fractionations were analysed by FT-i.r. and g.c.-m.s., and the results were compared in order to study the suitability of FT-i.r. for monitoring fractionations into compound classes. Slight modifications to the procedure previously used were needed to attain a good separation of aliphatics from light alkylated aromatics and hydroaromatics. Aliphatics, aromatics and neutral nitrogen compounds were well separated whereas phenols, which eluted all together in the same fraction, were mixed with basic nitrogen compounds. The similar composition of both samples enabled the accuracy and reproducibility of extrography to be checked. The composition of both coal-derived oils is briefly discussed in relation to their origin.