Liliana C. Koll

Transmetallations between aryltrialkyltins and borane: synthesis of arylboronic acids and organotin hydrides

Abstract Aryltrialkyltin compounds react with borane in THF to give mixtures of trialkyltin hydrides and arylboranes, which on hydrolysis give arylboronic acid in high yields. The arylboronic acids are easily separated and obtained free of organotins.

Stereoselective hydrostannation of substituted alkynes with trineophyltin hydride

Hydrostannation of mono- and disubstituted alkynes with trineophyltin hydride (1) leads to vinylstannanes in good to excellent yields, the configuration of the products depending on the reaction conditions. Thus, whereas hydrostannation under radical conditions leads stereoselectively to only one of the two possible products corresponding to an anti addition in 60–99% yield, the additions catalyzed by bis(triphenylphosphine)palladium dichloride gave mixtures of the syn adducts (60–79% yield). Full 1H-, 13C-, and 119Sn-NMR as well as mass spectra data of the organotin adducts are given.

Organotin compounds. IX: Reactions between trialkylstannyl-substituted esters and trimethylsilyl halides: exchange vs. hydrolysis

Abstract A study of the reactions between β- and ω-trialkylstannyl-substituted saturated methyl carboxylates (R  Me, n-Bu, Ph) and trimethylsilyl halides (X  Cl, Br, I) is reported. The results indicate that methyl β-(trialkylstannyl)propanoates react with trimethylsilyl halides to give alkyl/halide exchange products; no ester cleavage is observed even using organotin ester/silicon halide ratios of 1 4 . The reactions carried out with ω-trialkylstannyl-substituted esters show that the failure of methyl β-(trialkylstannyl)propanoates to give transesterification products is connected with the intramolecular coordination that exists in the methyl β-(halodialkylstannyl)propanoates, alkyl/halide exchange products, which prevents the coordination between the CO of the ester and the silicon halide. The results obtained also indicate that the alkyl/halide exchange reactions are much faster than the transesterification reactions. Evidence concerning the possibility that these halodealkylation reactions at tin might be a general property of tetralkyltin compounds is presented.

1,2-STEREOINDUCTION IN THE ASYMMETRIC HYDROSTANNATION OF (E)- AND (Z)-TRISUBSTITUTED ETHYLENES WITH (-)-MENTHYLDIMETHYLTIN HYDRIDE

Abstract Free radical hydrostannation of methyl ( 2 ) and (−)-menthyl ( 3 ) ( E )-2,3-diphenylpropenoates and ( Z )-2,3-diphenylpropenenitrile with (−)-menthyldimethyltin hydride ( 1 ) takes place with high diastereoselectivity. The observed 1,2-stereoinduction is explained taking into account that the combination of both allylic strain effects and the hyperconjugation existing between the β-trialkyltin substituent and the half filled carbon p orbital leads to particularly stable conformations in the intermediate radicals. These results, together with those reported earlier, indicate that it is possible to predict the stereochemistry of the hydrostannation products by considering the type of substituents attached to the olefinic bond and the preferred conformation of the intermediate radicals resulting from the addition of the organotin radical. These studies also demonstrate that it is possible to achieve asymmetric hydrostannations using organotin hydrides with chiral organic ligands. Full 1 H-, 13 C-, and 119 Sn-NMR data of the new organotin adducts are given.

1,2-Asymmetric induction in the radical addition of organotin hydrides to (−)-menthyl(E)-2,3-disubstituted propenoates

Abstract The results obtained in the free radical hydrostannation of (−)-menthyl(E)-2,3-diphenylpropenoate (1) with tri-n-butyl- and triphenyltin hydride, and of (−)-menthyl(E)-2-phenyl-2-butenoate (7) with trimethyltin hydride are reported. The absolute configuration of the new organotin adducts was determined by combining 1H- and 13C-NMR data with chemical correlation. The additions took place in all cases following a syn stereochemistry that led to diastereomeric excesses ranging between 73 and 100%. The observed stereochemistry is explained, taking into account both the allylic strain and the hyperconjugation with β-trialkyltin substituent existing in the intermediate radicals. Full 1H-, 13C- and 19Sn-NMR data are given.

Stereoselective hydrostannation: Synthesis and absolute configuration of (−)-menthyl 2,3-diphenyl-3-(trimethylstannyl) propanoates and derivatives

Abstract Free radical hydrostannation of (−)-menthyl ( E )-2,3-diphenylpropenoate ( 1 ) leads to a mixture of four adducts: two threo diastereoisomers (approx. 90%) and two erythro diastereoisomers (approx. 10%). Whereas threo diastereoisomers 2 (38%) and 3 (51.2%) could be isolated by column chromatography and fractional recrystallization, erythro diastereoisomers 4 and 4′ (6.5% and 4.3%) could not be separated. Bromodestannylation of 2 and 3 yielded two diastereoisomers in each case, 9–10 and 11–12 , respectively, which were isolated and characterized by spectroscopic methods. The reduction of bromo esters 9–12 with lithium aluminium hydride gave ( R )-(−)- and ( S )-(+)-2,3-diphenyl propanols 13 and 14 of known absolute configuration. Working back from the stereochemistry of 13 and 14 and taking into account the NMR data, the stereochemistry of their precursors was assigned. Full 1 H, 13 C, and 119 Sn NMR data are given.

Bromodestannylation reactions of some functionally substituted organotin compounds

Abstract Bromodestannylation reactions are reported for several functional substituted organotin compounds in carbon tetrachloride and acetonitrile as solvents. The reactions in carbon tetrachloride proceed with a high degree of retention of configuration at the carbon involved in the electrophilic substitution, while in a polar solvent there is an increase in the amount of inversion product formed. The electrophilic cleavage in the β-trialkylstannyl esters takes place with a complete reversal of the normal sequence of SnC bond cleavage by halogens; this is explained by tin assistance. The configuration of some 3-trialkylstannylpropanenitriles, β-bromonitriles and β-bromoesters are assigned. Full 1H, 13C and 119Sn NMR data are given.

Ultrasound promoted Barbier reactions and Csp3–Csp2 Stille coupling for the synthesis of diarylmethanes and substituted benzophenones

Here we present the preparation of a variety of diarylmethanes obtained via ultrasound Stille coupling under palladium catalysis between some substituted aryl compounds and benzyltributyltin compounds generated through sonicated Barbier reaction in a very short time reaction and excellent yield. The study reported below compares different methods to optimize the synthesis of usually unstable benzyltin derivatives and is another contribution to the investigation of Csp(3)-Csp(2) coupling process involving benzyl-aryl reagents. Substituted carboxylated benzophenones were easily prepared in a very good yield by oxidation of some diarylmethanes.

Efficient Routes to Racemic and Enantiomerically Pure (S)-BINOL Diesters

Abstract A systematic study for esterification procedures to the synthesis of BINOL diesters is described. Reaction conditions with trifluoracetic acid anhydride (TFAA) and 85% H3PO4 were selected as the best procedure to prepare enantiomerically pure (S)-1,1′-bi-2-naphthol (BINOL) diesters VIII to XI with almost quantitative yields and very short reaction times. [Supplementary materials are available for this article. Go to the publishers online edition of Synthetic Communications® for the following free supplemental resources: Full experimental and spectral details.] GRAPHICAL ABSTRACT

Synthesis of Organotin Substituted Tricyclic Macrodiolides

The radical addition of triorganotin hydrides, R3SnH (R = n-butyl, phenyl, neophyltin), to four unsaturated diesters of (11R,12R)-9,10-dihydro-9,10-ethaneanthracene-11,12-dimethanol leads to products of cyclohydrostannation with an average yield of around 80%. Whereas the addition of these hydrides to diacrylate and dimethacrylate leads to the expected mixtures containing two and four distereoisomeric cyclized products respectively, the addition to di-2-methyl- and di-2- phenylcinnamate yields only four out of the sixteen possible stereoisomers. The observed high stereoselectivity is consistent with a radical tandem cyclohydrostannation mechanism. Full proton ( 1 H), carbon 13 ( 13 C) and tin 119 ( 119 Sn) nuclear magnetic resonance (NMR) data are given.