Preparation of N-arylpiperazines and other N-aryl compounds from aryl bromides as scaffolds of bioactive compounds

Aryl bromides are coupled with N-compounds to give the corresponding arylamines in the presence of a palladium catalyst, a suitable ligand, and a weak base. The catalysts perform well for a large number of different starting material combinations at 100-150 °C with drops of toluene or without solvent, and with low catalyst levels (0.12 mol % Pd). The low catalyst amount makes the process environment friendly.     

Sequential Baylis-Hillman/RCM protocol for the stereoselective synthesis of (+)-MK7607 and (+)-streptol

Sequential Baylis-Hillman/ring-closing metathesis (RCM) approach toward the total synthesis of (+)-MK7607 and (+)-streptol starting from (R,R)-tartaric acid is reported.     

Chemoenzymatic syntheses of the linear triquinane-type sesquiterpenes (+)-hirsutic acid and (−)-complicatic acid

Formal total syntheses of the natural enantiomeric forms of the title sesquiterpenes 1 and 2 have been achieved using, as starting material, the readily available and enantiomerically pure cis-1,2-dihydrocatechol 4 derived from the whole-cell biotransformation of toluene.     

Total synthesis of (+)-xyloketal D, a secondary metabolite from the mangrove fungus Xylaria sp.

(+)-Xyloketal D was prepared in a one-pot multistep domino reaction by heating optically active 5-hydroxy-4-methyl-3-methylenepentan-2-one (R) in toluene with 2,4-dihydroxyacetophenone. The absolute configuration of the natural product was confirmed by preparation of the starting enone from a lactone of established absolute configuration.     

Chemoenzymatic approaches to the montanine alkaloids: a total synthesis of (+)-nangustine

The synthesis of (+)-nangustine [(+)-2] has been achieved, for the first time, using the enantiomerically pure cis-1,2-dihydrocatechol 3 as starting material. The latter compound is available, in multi-gram quantities, through a whole-cell-mediated biotransformation of chlorobenzene using genetically engineered organisms that over-express the responsible enzyme, namely toluene dioxygenase. Since the enantiomer of compound 3 is available by related means, the present work also represents a formal total synthesis of the montanine alkaloid (−)-nangustine [(−)-2]. Single-crystal X-ray analyses of compounds 13 and (+)-2 are reported.     

A chemoenzymatic total synthesis of the hirsutene-type sesquiterpene (+)-connatusin B from toluene

The first total synthesis of the hirsutene-type sesquiterpenoid natural product (+)-connatusin B (2) is reported. The cis-1,2-dihydrocatechol 3, which is obtained in enantiomerically pure form via the enzymatic dihydroxylation of toluene, served as the starting material. Diels-Alder cycloaddition and oxa-di-π-methane rearrangement reactions represent key chemical steps in the reaction sequence leading to the cyclopropane ring-fused linear triquinane 14. Reductive cleavage of the three-membered ring within this framework and various functional group interconversions then provide the title compound 2.     

Stereoconvergent preparation of chiral vinylsilanes by cuprate substitution of α-acetoxyallylsilanes. Application to the synthesis of (S)-(+)-bishomomanicone

Enantiomerically enriched (E)- and (Z)-configured α-acetoxyallylsilanes have been prepared starting from a chiral acylsilane bearing an asymmetric unit at the silicon portion. Treatment of these compounds with organocuprates afforded the respective vinylogous substitution products in high yields and high stereoselectivities. The transformations proceed essentially by complete anti attack of the nucleophiles to the allylic acetates and predominantly via transition states leading to the (E)-configured vinylsilane products. By the proper choice of the double bond geometry in the starting material, the configuration of the newly formed stereogenic center can be controlled. The method represents a new and flexible entry into chiral vinylsilanes that can be used for subsequent transformations. As an example, the α,β-unsaturated γ-chiral, naturally occurring ketone (S)-(+)-bishomomanicone was synthesized with this method, which represents the first synthetic access to this compound.     

An efficient total synthesis of (−)-anamarine

An efficient synthesis of (−)-anamarine is described using d(+)-mannitol and (R)-epichlorohydrin. The synthesis is achieved starting from easily accessible d(+)-mannitol using a selective benzoylation, regioselective epoxide ring opening, a selective acetonide deprotection, tosylation and cross metathesis reaction.     

Total syntheses of (+)- and (−)-syringolides 3 and of (+)- and (−)-syributins 1, 2 and 3

The first total syntheses of (−)-syringolide 3, (+)-syributin 3 and their unnatural enantiomers (+)-syringolide 3 and (−)-syributin 3 using a common intermediate as starting material are described. In addition, total syntheses of (−)- and (+)-syributins 1 and 2 were accomplished by means of the same methodology.     

Ti(III)-promoted cyclizations. Application to the synthesis of (E)-endo-bergamoten-12-oic acids. Moth oviposition stimulants isolated from Lycopersicon hirsutum

The Ti(III)-promoted radical cyclization of epoxyenone 8 is described as the key step to access the diol 10 as a convenient starting material of the target molecules. The synthesis of β-(E)-endo-bergamoten-12-oic acid 2a from (+)-8,9-epoxycarvone 8 was successfully achieved by Suzuki-Miyaura coupling of the terminal alkene 20 with β-iodomethacrylate 21c, followed by deprotection and dehydration processes. Moreover, synthesis of the α-(E)-endo-1-hydroxy-bergamoten-12-oic acid derivative 34 was achieved by iterative elongation processes of the diol 10 lateral chain.     

First total synthesis of (+)-crassalactone A

A simple and highly efficient first total synthesis of cytotoxic (+)-crassalactone A starting from (R)-mandelic acid is described. The strategy involves the osmium tetroxide-catalyzed cis-hydroxylation and the stereoselective addition of ethyl lithiopropiolate to a chiral aldehyde intermediate as key steps.     

Stereoselective total synthesis of (+)-cardiobutanolide and (+)-3-epi-cardiobutanolide from diacetone d-glucose

A chiron approach starting with 3-O-benzyl-1,2-O-isopropylidene-α-d-xylo-pentodialdo-1,4-furanose utilizing a Grignard reaction, Mitsunobu stereoinversion, ethyl diazoacetate addition, and selective reduction of the ketone is employed as a key step for the total synthesis of (+)-cardiobutanolide described; a similar strategy is also reported for the first total synthesis of (+)-3-epi-cardiobutanolide.     

Short synthesis of stenusine and norstenusine, two spreading alkaloids from Stenus beetles (Coleoptera: Staphylinidae)

Each of the both spreading alkaloids stenusine and norstenusine could be synthesized starting from commercially available 3-picoline in a two-step synthesis in yields of 74% and 67% in gram scale. The stereoisomeric ratio of the synthesized (+)-stenusine is similar to that of stenusine from Stenus comma.     

Synthesis of enantiopure bis-isoxazolines from (4R)-(+)-4-acetoxycyclopent-2-enone

(4R)-(+)-4-Acetoxycyclopent-2-enone was used as a starting material in the stereoselective synthesis of enantiopure bis-isoxazolines.     

Versatile synthetic methods for the engineering of thiophene-substituted Bodipy dyes

Novel thienyl-borondiazadipyrromethene (Bodipy) dyes have been prepared using boronic acids or boronate reagents as cross-coupling mediators. A key dichloro/bromo-Bodipy starting material appears to be a useful starting material for such coupling reactions, enabling the synthesis of various symmetrically and unsymmetrically substituted thienyl-dyes. An alternative means of introducing thienyl substituents is through Knoevenagel substitution in the 3 and 5 positions of Bodipy by reaction with a formyl-functionalized thiophene derivative, resulting in systems of extended delocalization. All these Bodipy derivatives are stable and exhibit pronounced fluorescence on irradiation in the S₀→S₁ transition.     

Synthesis of (+)-striatene: confirmation of its stereostructure

The first enantioselective synthesis of natural striatene (+)-1, isolated from liverwort Ptychanthus striatus, starting from commercially available (R)-Pulegone is described. Its stereostructure was confirmed by X-ray analysis of a 3,5-dinitrobenzoate derivative obtained from a key intermediate and its high optical purity was verified by chiral HPLC.     

A general and enantiodivergent method for the asymmetric synthesis of piperidine alkaloids: concise synthesis of (R)-pipecoline, (S)-coniine and other 2-alkylpiperidines

A simple and very efficient protocol for the preparation of highly enantioenriched 2-alkylpiperidines has been set up, which allows the preparation of the final heterocycles with any wanted configuration at the stereogenic center starting from the same starting material. The key step of the synthesis relies on a diastereodivergent aza-Michael reaction protocol using the readily available and cheap reagent (+)-(S,S)-pseudoephedrine as chiral auxiliary.     

Concise chemoenzymatic synthesis of gabosine A,ent-epoformin and ent-epiepoformin

An efficient methodology has been developed to synthesize three related enantiomerically pure natural and unnatural compounds, based on a chemoenzymatic approach. We confirmed the usefulness of 3-methyl-cis-1,2-cyclohexadienediol derived from a biotransformation of toluene, as a starting material in a rational and versatile route to produce gabosines and methyl substituted epoxycyclohexenones.     

Polyhydroxylated pyrrolizidines. Part 6: A new and concise stereoselective synthesis of (+)-casuarine and its 6,7-diepi isomer, from DMDP

A new synthesis for (+)-casuarine (1) and its 6,7-diepi isomer (15) in a stereocontrolled manner, is reported herein. An appropriately protected polyhydroxylated pyrrolidine, such as (2R,3R,4R,5R)-3,4-dibenzyloxy-2′-O-tert-butyldiphenylsilyl-2,5-bis(hydroxymethyl)pyrrolidine (3, protected DMDP), easily available from d-fructose, was chosen as the chiral starting material. Compounds 1 and 15 were obtained from 3, in seven steps, in a 23.2 and 20.5% overall yields, respectively.     

Direct alkenylation of arylamines at the ortho-position with magnesium alkylidene carbenoids and some theoretical studies of the reactions

1-Chlorovinyl p-tolyl sulfoxides were synthesized from ketones and chloromethyl p-tolyl sulfoxide in high yields. Treatment of the sulfoxides with isopropylmagnesium chloride at −78 °C in toluene gave magnesium alkylidene carbenoids (α-chloro alkenylmagnesium chlorides), which were treated with N-lithio arylamines to afford ortho-alkenylated arylamines in moderate yields. The reaction, in some cases, proceeded in a highly stereospecific manner at the carbon bearing the chlorine and the sulfinyl group. The structures of the α-chloro alkenylmagnesium chlorides and the reactivity of the N-lithio meta-substituted anilines were studied at the B3LYP and MP2 levels of theory with the 6-31(+)G* basis set. This reaction offers a quite novel and direct alkenylation of arylamines at the ortho-position of the aromatic ring.