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Individual Mn12 single-molecule magnets have been investigated by means of scanning tunneling spectroscopy at room temperature. Current-voltage characteristics of a Mn12 derivative are studied in detail and compared with simulations. A few-parameter scalar model for ballistic current flow through a single energy level is sufficient to describe the main features observed in scanning tunneling spectra of individual Mn12 molecules and offers a deeper insight into the electronic transport properties of this class of single-molecule magnets. In addition, distance-voltage spectroscopy performed on individual Mn12 molecules reveals a possibility to identify the orientation of the molecular easy axis. The results indicate a preferential orientation of the easy axis of the molecules nearly perpendicular to the surface.

X-Ray-diffraction analysis of tBu2CNSCl (4b) revealed an almost linear CNS unit with an SN bond order of ca. 1.9 (Fig. 1), in agreement with the structure of a 1-thia-2-azoniaallene chloride. With SCl2 and SbCl5, compound 4b was transformed into the imidosulfurous dichloride 6 (Scheme 2). With morpholine, compounds 4b and 6 afforded the sulfenamide 7and the aminosulfonium salt 8, respectively. The (diarylmethylene)amidosulfenyl chlorides 4g,h,i reacted with SbCl5 to give SbCl salts of the 1,2-benzisothiazoles 9a,b,d, most likely via 1-thia-2-azoniaallene intermediates 2 (Scheme 3).

The indene derivative 7 and the 1,2,2,3-tetrasubstituted cyclopentane derivative 8 have been synthesized in three steps starting from the Hajos-Wiechert ketone 1.

α-Alkylation of the α,β-unsaturated ketone 1 at C-4 has been achieved by thioalkylation of the corresponding zinc dienolate with α-chlorosulfides of type 2. The desulfurization of the β-(phenylthio) ketones 4 leads directly to the 4-substituted hexahydroinden-5-ones 5.

A total synthesis of (±)-chokol A (rac-12) was accomplished in five steps by starting from the α,β-unsaturated ester (E)-2 in an overall yield of 24%. The key step of this synthesis is the tandem conjugate addition/Dieckmann cyclization of the cuprate derived from vinyl bromide 9 with the α,β-unsaturated ester (E)-2.

The addition of (trimethylsilyl)propargylmagnesium bromide (9) to aldehydes afforded predominantly the allenylic alcohols rac-10. The regioselectivity of this addition changes dramatically when organocerium reagents were used for the addition. In this case nearly exclusive formation of the homopropargylic alcohols rac-8 was observed. Highest selectivity for this process was obtained when cerium(III) isopropoxide (13) was used as a precursor for the formation of the organocerium reagent.

An α-alkylidation of cyclopentanone was achieved in two reaction steps in an overall yield of 20 to 79% via a zinc chloride-catalyzed thioalkylation of the zinc enolate of methyl 2-oxocyclopentanecarboxylate (3) and subsequent saponification/desulfurization of the β-(phenylthio) ketone intermediates 5. For the saponificatioddesuiurization step DABCO proved to be the reagent of choice and superior to the use of alkali or magnesium halides.

The X-ray structure of (+)-13-tert-butoxy-3aa,43,5,6,-7,7a-hexahydro-7a3-methyl-5-oxo-4a-indancarboxylic acid methyl ester is reported, in which the six-membered ring adopts a pseudo chair conformation and the five-membered ring an envelope conformation.

An α-alkylation of the 2-methylcycloalkanones 1 and 4 at the higher substituted carbon can be achieved by thioalkylation of the corresponding zinc enolates with the α-chlorosulfides 3. The desulfurization can be carried out with either Raney nickel or lithium in diethylamine for compounds which contain double or triple bonds.

The lithium or potassium derivative of diethyl isocyanometh-ylphosphonate (1) reacts with epoxides in the presence of boron trifluoride-diethyl ether to provide the diethyl 3-hy-droxy-1-isocyanoalkylphosphonates rac-3. The corresponding mesylates rac-4 undergo a base-mediated cyclization to the diethyl 1-isocyanocyclopropylphosphonates rac-5. Acidic hydrolysis affords the diethyl l-aminocyanocyclopropylphos phonates roc-6, which upon treatment with trimethylsilyl iodide yield the 1-aminocyclopropylphosphonic acids rac-7. A base-mediated cycloalkylation of 1 with dibromoalkanes 10 gives the diethyl 1-isocyanocycloalkylphosphonates 11 which are suitable precursors for the achiral l-aminocycloal-kylphosphonic acids.

The diketopiperazine cyclo(-L-Val-Gly-) (1) can be 0-alkylated under mild acidic reaction conditions with the alkyl trichloroacetimidates 2 to the corresponding bisalkyl bislactim ethers. Alkylation of the bisbenzyl bislactim ether anion of cyclo(-L-Val-Gly-) 4 c with benzyl bromide and subsequent hydrolysis with aqueous trifluoroacetic acid afforded D-phenyl-alanine benzyl ester (8) with an enantiomeric excess of >95%.

Enantiomerically pure 3- and 4-substituted phosphonic acid derivatives 5 of pyroglutamic acid were prepared by a Michael addition of the lithiated (+)-camphor derivative 2 to α,β-unsaturated esters and subsequent hydrolysis. The reduction of the lactams 5 with LiBH4/BF3·OEtz afforded substituted phosphonic acid analogues 7 of proline.

The substituted 2-benzazepines 4, 5 and 12 were prepared by a base-mediated ring expansion reaction of mesylates la- e, which were synthesized in 4 to 5 steps by starting from benzolactams 6.

allo-Coronamic acid (1) was synthesized in five steps enantiomerically and diastereomerically virtually pure by starting from the bislactim ethers of cyclo(-L-Val-Gly-) (3a) or cyclo- (-L-tert-Leu-Gly-) (3b) in an overall yield of 31%. The key step of this synthesis is the intramolecular alkylation of the lithium azaenolate derived from the allylic chloride 4.

A novel method for the synthesis of N-methylserines has been developed. The oxazolidines 4 are formed by condensation of the serine methyl esters 1 with formaldehyde. These intermediates are subsequently reduced to the N-methylserine methyl esters 9 by an acid-catalyzed ring opening via their iminium ions 2 with triethylsilane/trifluoroacetic acid.

The cyclopropanation of the bislactim ethers 3 with diiodo-hymethanes and diethylzinc proceeds in good yields and with high diastereoselectivities, affording the cyclopropyl bislactim ethers 6. Protection of the hydroxy group and subsequent hydrolysis furnish virtually enantiomerically and diastereo merically pure methyl (2R,3S)-2-amino-3-cyclopropyl-3-droxyalkanoates 8. The bislactim ethers of type 3 are obtained by a known method diastereomerically pure, starting from the bislactim ether of cycle(-L-Val-Gly-).

The titanium derivative 2 of the bislactim ether 1 of cyclo(-LVal-Gly-) reacts with aldehydes and ketones 3 highly diastereoselectively to give the syn-addition products 4. Upon hydrolysis with diluted trifluoroacetic acid the compounds 4 yield besides methyl L-valinate the (2R,BS)-threo-serinme ethyl esters 5.