Martin Nilsson

Chloro- and iodotrimethylsilane-activated additions of organocopper compounds to enones and enoates

Abstract Organocopper compounds add to enones and enoates in the presence of chlorotrimethylsilane in ether giving the conjugate adducts in preparatively useful yields via the silyl enol ethers. Presence of lithium iodide is important and excess of chlorotrimethylsilane accelerates the reactions. The combination of organocopper compound, iodotrimethyl-silane and dimethyl sulfide gave faster reactions and very high yields, particularly in dichloromethane, where the reaction mixtures gradually became homogeneous.

Synthesis of Schiff Bases Forming the First Room Temperature Ferroelectric Liquid Crystal—The Mora Series

Abstract Condensation of chiral S-4-(6-methyl)octyloxy-2-hydroxybenzaldehyde (S-4-0- (6-methyl)octylresorcylaldehyde) with 4-alkylanilines (the MORA series, 3) gives low-melting Schiff bases showing chiral smectic C phases at or slightly above room temperature. The previously known MBRA series (4-0- (2-methyl)-butyl- resorcylidene-4-alkylanilines, 1) has been extended by MBRA 4 and 12, both showing low-temperature smectic phases. Bis (S, S-4-(2-methylbutyloxy-2-hydroxybenzylidene)-2-chloro-1,4-phenylene-diamine shows a cholesteric blue phase between 174 and 175 °C.

From 2-thienylcopper couplings to trimethylsilyl-promoted organocopper additions

Abstract In this paper we continue a 2-thienylcopper line started about twenty years ago with the cross-coupling with iodobenzenes in quinoline. We now report a preparative and NMR study of the favourable influence of trimethylchlorosilane on the conjugate addition of lithium methyl(2-thienyl)cuprate to methyl cinnamate and of 2-thienylcopper and butylcopper to 4-phenyl-3-propen-2-one. NMR spectra of lithium methyl(2-thienyl)cuprate in tetrahydrofuran show the presence of two different organocuprate species ( A and B ). Trimethylchlorosilane strongly favours conjugate addition to methyl cinnamate at even −60°C and also favours form B (then presumably complexed by TMSCl). Thus again 2-thienylcopper- has proved itself as a practical and illustrative tool in organocopper chemistry.

Stereoselectivity in the transfer of the 2-(1-dimethylaminoethyl)phenyl group, R*, from LiR* 2Cu and Li(R*) (2-thienyl)Cu to enones

Abstract One diastereomer is formed in large excess (98 – 76 % diastereomeric excess) on addition of the 2-(1-dimethylaminoethyl) phenyl group, R * , to 3-penten-2-one, 2-cyclohexenone, 4-phenyl-3-buten-2-one, and 5-phenyl-2,2-dimethyl-4-penten-3-one.

Organocopper-iodosilane combinations in conjugate additions

Abstract This paper concerns new possibilities opened by the addition of (mono)organocopper compounds and iodotrimethylsilane (TMSI) to α,β-unsaturated ketones and esters giving the silyl enol ethers and ketene acetals, respectively. We demonstrate the homogeneous addition of methylcopper-tributyl-phosphine-iodotrimethylsilane to methyl cinnamate, the use of organocopper-bromotrimethylsilane combinations, the dominating formation of Z-silyl enol ethers on conjugate addition of methyl- and butylcopper/TMSI to benzalacetone, and the formation of silyl enol ethers in other additions of organocopper compounds and TMSX to conjugated ketones. The Z-selectivity for addition to benzalacetone corresponds tos-cis conformations in π-complexes between copper (I) chloride and 1-penten-3-one or 3-buten-2-one. The stereoselectivity could support a reaction path via π-complexes between organocopper-iodotri-methylsilane complexes and s-cis conformers of the substrates.

2-Arylpyridines from 2-pyridylcopper/triphenylphosphine and iodoarenes

Abstract 2-Arylpyridines are formed rather selectively in 50 to 80 % yields from 2-pyridylcopper and unactivated iodoarenes in the presence of one to two mol triphenylphosphine in toluene around 100 °C. The selectivity may be due to the ability of the copper(I) iodide-triphenylphosphine complex as a leaving group or may be discussed in terms of oxidative addition/reductive elimination. The unsymmetric coupling reaction may be general since the coupling of phenylcopper/triphenylphosphine with 2-iodopyridine also gives 2-phenylpyridine.

Addition of organocopper reagents to allylic acrylates — the preparation of γ, δ-unsaturated acids and subsequent functionalization to γ-lactones

Abstract Conjugate addition of monoorganocopper compounds with iodotrimethylsilane (TMSI) or lithium diorganocuprates, with or without halosilanes, to allylic acrylates give allylic silyl ketene acetals/ester enolates. These can undergo Claisen rearrangement to give diastereomeric mixtures of γ, δ-unsaturated acids after aqueous work-up. For organocuprates, the diastereomeric ratio is strongly affected by the halosilane. Either diastereomer can be obtained as major product by proper choice of copper reagent. Cyclization of the acids followed by reduction gives γ-lactones in good yields. A copper iodide/dimethyl sulfide complex is introduced as an excellent precursor to organocopper reagents.

Reactions of methylcopper and chiral organocuprates with 1-nitro-2-phenylethene and of lithium dimethylcuprate with methyl 3(nitrophenyl)propenoates

Abstract Organocopper compounds like methylcopper, lithium dimethylcuprate, chiral lithium methyl-( S )-2(1-dimethylaminoethyl)-phenylcuprate and lithium menthoxy(methyl)cuprate react with 1-nitro-2-phenylethene to give the conjugate addition product 1-nitro-2-phenylpropane in moderate yields. In the reaction with lithium methyl-( S )-2(1-dimethylaminoethyl)phenylcuprate 2% asymmetric induction was obtained. The reaction between lithium dimethylcuprate and methyl 3(4-nitrophenyl)propenoate gave the corresponding azoxy compound and no conjugate addition product, while methyl 3(3-nitrophenyl)propenoate gave some conjugate addition.

Conjugate addition with 2-pyridylcopper and lithium 2-pyridylcuprates

Abstract 2-Pyridylcopper/dibutyl sulfide, 2-pyridylcopper/tributylphosphine, lithium di(2-pyridyl)cuprate and lithium (2-pyridyl)(phenyl)cuprate all add the 2-pyridyl group to 4-phenyl-3-buten-2-one in good yields. The cuprates also add the 2-pyridyl group to ethyl 3-phenylpropenoate.

Diastereoselectivity in iodotrimethylsilane-promoted conjugate additions of organocopper reagents to chiral α,β-unsaturated imides and amides

Abstract Conjugate additions of MeCu, PhCu and BuCu to the chiral enoylimides 2 a-c in the presence of iodotrimethylsilane and lithium iodide in THF give the adducts, 4a-c in yields above 90 % and diastereoselectivities from 80 to 93%. The dominating diastereomers are different from those formed with LiR2Cu/TMSCl or in copper(I)-mediated addition of Grignard reagents. Corresponding additions to enoylamides of O-tritylprolinol also give high yields of conjugate adducts, but lower diastereoselectivities, with dominating configuration in the acyl part opposite to those from the imides.