A Stereospecific Synthesis of (E,Z)-α, β-γ, δ-Diunsaturated Aldehydes,Ketones, and Esters Using the Benary Reaction

The reaction between (Z)-1-alkenyllithium and (E)-β-(N, N-dialkylamino)-α, β-alkenals, (E)-β-(N, N-dialkylamino)-α, β-alkenones or (E)-β-(N, N-dialkylamino)-α, β-alkenoic esters yields mainly (E, Z)-α, β-γ, δ-diunsaturated aldehydes, ketones, or esters and is therefore highly stereospecific.     

Reaction of Carbon Anions With Iron α,β-Unsaturated Ketimine Complexes

Complexes (η⁴-PhCH=CHCR=NPh)Fe(CO)₃, where R=H(1a) and CH₃ were synthesized in excellent yield from the reaction of the corresponding α,β-unsaturated ketimines with excess Fe₂(CO)₉. Reaction of la with (Ph)₂CHLi and (CH₃)₂(NC)CLi at ?78°C or ambient temperature followed by acid quenching gave trans-PhCH=CHCHRNHPh, where R=CHPH₂ and C(CH₃)₂CN, respectively, in good yield. In the presence of 1 atm. of CO the reaction of 1a with (CH₃)₂(NC)CLi, followed by CuCl₂ oxidation resulted in the formation of a carbamyl choride, trans-PhCH=CHCH[C(CH₃)₂CN]N(Ph)COCl. This species was converted to a carbamate compound trans-PhCH=CHCH[C(CH₃)₂ - CN]N(Ph)COOCH₃ in MeOH in the presence of Ag⁺.     

The Clemmensen Reduction of α, β-Unsaturated Ketones

Eleven structurally different α, β-unsaturated ketones were subjected to the Clemmensen reduction under anhydrous conditions using amalgamated zinc, hydrogen chloride in a solution of ethyl ether, and acetic anhydride. In all cases but one the formation of cyclopropyl acetates was observed. 4-Methyl-3-penten-2-one, methyl vinyl ketone, 2-isopropylidene-1-cyclopentanone, and 2-cyclohepten-1-one led to substituted cyclopropyl acetates. Stereospecific reactions were found with 2-ethylidene-1-cyclopentanone, 2-benzylidene-1-cyclohexanone, and methyl 1-cyclohexenyl ketone, whereas 3-penten-2-one, 3-methyl-3-buten-2-one, and 2-methyl-2-cyclohexen-1-one afforded mixtures of the isomeric cyclopropyl acetates. These results are interpreted in terms of the intital formation of an allylic anion which undergoes electrocyclic closure. A stereospecific course is followed when geometric constraints permitted. Exceptions are discussed.     

Trityl Cation-Catalyzed Hosomi-Sakurai Reaction of Allylsilane with β,γ-Unsaturated α-Ketoester to Form γ,γ-Disubstituted α-Ketoesters

(Ph₃C)[BPh(^F)₄]-catalyzed Hosomi-Sakurai allylation of allylsilanes with β,γ-unsaturated α-ketoesters has been developed to give γ,γ-disubstituted α-ketoesters in high yields with excellent chemoselectivity. Preliminary mechanistic studies suggest that trityl cation dominates the catalysis, while the silyl cation plays a minor role.     

Synthese von (R)-β, β-Carotin-2-ol und (2R, 2′R)-β, β-Carotin-2,2′-diol

Synthesis of (R)-β, β-Caroten-2-ol and (2R, 2′R)-β, β-Carotene-2,2′-diol Starting from geraniol, the two carotenoids (R)-β, β-caroten-2-ol ( 1 ) and (2R, 2′R)-β, β-carotene-2,2′-diol ( 3 ) were synthesized. The optically active cyclic building block was obtained by an acid-catalysed cyclisation of the epoxide (R)- 4 . The enantiomeric excess of the product was > 95 %.     

The Synthesis of β,γ- and α,β-Unsaturated Aldehydes via Polyene Epoxides

A substitute for the Darzens glycidic ester synthesis for converting unsaturated ketones or aldehydes into the homologated β,γ- or α,β-unsaturated aldehydes employing sulfur ylides is described. The carbonyl group is converted into the unsaturated oxirane which is then rearranged to the new aldehyde. High yields of isomerically pure aldehydes are available by this method and the process is of practical importance in the conversion of β-ionone into the β-C₁₄-aldehyde, a key intermediate in the Isler synthesis of vitamin A. The efficient preparation of α- and β-cyclocitral by the novel process is also described.     

Rhodium(II)-Catalyzed Decomposition of β,γ-Unsaturated Diazo Compounds

The Rh^II-catalyzed decomposition of β,γ-unsaturated diazo ketones 1 in the presence of MeOH leads via vinylogous Wolff rearrangement to γ,δ-unsaturated esters 6 (Schemes 1 and 2). A modest asymmetric induction is achieved when the reaction is carried out with chiral tetrakis(pyrrolidinecarboxylato)- or tetrakis(oxazolidinonato)dirhodium(II) complexes. Vinyl and phenyl diazoacetates 11 and 20 , respectively, or 1-diazo-3-phenyl-propan-2-one ( 25 ), when subjected to the same reaction conditions, react by OH insertion with MeOH (Schemes 3–5). In the absence of MeOH, phenyl diazoacetates 20 and 25 undergo intramolecular CH insertion to 22 and 26 , respectively. Intramolecular CH insertion occurs with N-aryldiazoamides 23 even in the presence of MeOH (Scheme 5).     

Lipophilic Functionalized Cobyrinic-Acid Derivatives. Part 1. Cobester α-monoacids (α,α,α,β,β,β-hexamethyl α-hydrogen Coα, Coβ-dicyanocobyrinates)

The four α,α,α, β,β,β,-hexamethyl α-hydrogen Coα, Coβ-dicyanocobyrinates 2b, d–f , with a free b-, d-, e-, and f-propionic-acid function, respectively, were prepared by partial hydrolysis of heptamethyl Coα, Coβ-dicyanocobyrinate (cobester; 1 ) in aqueous sulfuric acid. The cobester monoacids 2b, d–f were obtained as a ca. 1:1:1:1 mixture which was separated. The monoacids were purified by chromatography and isolated in crystalline form. The position of the free propionic-acid function was determined by an extensive analysis of 2b, d–f using 2D-NMR techniques; an analysis of the C,H-coupling network topology resulted in an alternative assignment strategy for cobyrinic-acid derivatives, based on pattern recognition. Additional information on the structure of the most polar of the four hexamethyl cobyrinates, of the b-isomer 2b , was also obtained in the solid state from a single-crystal X-ray analysis. Earlier structural assignments based on 1D-NMR spectra of the corresponding regioisomeric monoamides 3b, d–f (obtained from crystalline samples of the monoacids 2b, d–f ) were confirmed by the present investigations.