Synthesis and structure of some cis-and trans-myrtanylstannanes

Enantiomerically pure cis- and trans-myrtanylstannanes cis-MyrSnPh₃ (1), trans-MyrSnPh₃ (2), cis-MyrSnPh₂Cl (3), trans-MyrSnPh₂Cl (4), cis-MyrSnPhCl₂ (5), trans-MyrSnPhCl₂ (6), cis-MyrSnCl₃ (7), trans-MyrSnCl₃ (8) were synthesized and fully characterized by ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy. The molecular structures of 1, 3, 6, 7, and [trans-MyrSn(OH)Cl₂ · H₂O]₂ (8a) a hydrolysis product of 8, were determined by X-ray crystallography.     

The rhodophytin and chondriol natural products; structures of several new acetylenes from laurencia, and a reassignment of structure for cis-rhodophytin

The structures of five new halogenated vinyl acetylenes are described which are natural products from various species of the red seaweed Laurencia. The structure of epoxyrhodophytin (1) was determined by spectral, chemical, and X-ray diffraction analyses. The structures of trans-rhodophytin (5) and trans-chondriol (8) are based on chemical and spectral comparisons with the previously reported compounds cis-rhodophytin (4) and cis-chondriol (7). The structures of cis-chondrin (14) and trans-chondrin (15) were secured by synthesis from cis- and trans-chondriol, respectively. The reactivity of these enol-ethers to various conditions of catalytic hydrogenation has been examined in detail. Hydrogenation yields an unexpected and facile incorporation of oxygen into the reaction products. Based upon these studies, and upon combustion analysis, the structure of rhodophytin has been revised as the vinyl ether rather than the vinyl peroxide originally proposed.     

Synthesis of trans-vaccenic acid and cis-9-trans-11-conjugated linoleic acid

The preparation of the monounsaturated fatty acid, trans-vaccenic acid 4 (TVA), using both Wittig and one-pot Julia-Kocieński olefination protocol, was achieved in good yield. Similarly a Wittig approach was employed for the stereoselective synthesis of cis-9-trans-11-conjugated linoleic acid 2 from trans-2-nonenal and (8-carboxyoctyl)triphenylphosphonium bromide 12.     

Stereochemical studies—XIII: Cyclic aminoalcohols and related compounds—VI synthesis of the four 2-amino-4-t-butylcyclopentanol isomers

From diethyl 3-t-butyladipate (5), via cis- and trans-4-t-butylcyclopentene-1,2-oxide (31, 32) as key compounds, the syntheses of cis-2-amino-cis-4-t-butylcyclopentanol (1), cis-2-amino-trans-4-t-butylcyclopentanol (2), trans-2-amino-cis-4-t-butylcyclopentanol (3) and trans-2-amino-trans-4-t-butylcyclopentanol (4) have been achieved. 1, 3 and 4 were also synthesized from the corresponding 2-hydroxy-4-t-butylcarboxylic acids by Curtius degradation of the hydrazides (11, 18, 19). The steric course of process leading to the above compounds is discussed.     

Characterization of the photoisomers from cis- and trans-chlordanes, trans-nonachlor and heptachlor epoxide

Irradiation of acetone solutions of trans-chlordane (4a) and trans-nonachlor (4b) with UV light produces new half-cage photoisomers (5a or 6a and 5b or 6b, respectively) with bridging that differs from that of the photoisomers (2 and 8a) obtained from cis-chlordane (1b) and heptachlor epoxide (7). A new photoisomer (10) obtained from heptachlor epoxide is transformed into photoisomer 8a on further irradiation. Detailed PMR and ¹³C-NMR studies establish the structures of the new photoisomers and permit a decision between alternative formulations for the structures of the half-cage photoisomers of heptachlor epoxide and cis-chlordane,     

The conversion of 3,4-cis- to 3,4-trans-cannabinoids

An investigation of the conversion of Δ¹-3,4-cis-THC 1a to Δ⁶-3,4-trans-THC 2a with BBr₃ is described. By use of 1a of known optical purity it was determined that the main epimerization occurs at C-4. The small loss of optical purity observed during formation of 2a results from either competitive epimerization at C-3 or a racemization process. The conversion of 3,4-cis- to 3,4-trans-HHCs proceeds with exclusive C-4 inversion.     

Alkaline hydrolysis of N-bromoiminothianthrene derivatives

5-(N-Bromo)iminothianthrene (2) and 5-(N-bromo)iminothianthrene 10-oxide (5) and 10,10-dioxide (8) were prepared and their alkaline hydrolyses were studied. The compound 2 and cis-5-(N-bromo)iminothianthrene 10-oxide (cis-5) afforded the corresponding sulfoximine exclusively. While, unexpectedly, both trans-5-(N-bromo)iminothianthrene 10-oxide (trans-5) and 8 afforded mainly de-brominated products, trans-5-iminothianthrene 10-oxide (trans-4) and 5-iminothianthrene 10,10-dioxide (7), respectively. In these cases, 5-iminothianthrene 5,10-dioxide (6) (Z- and E-mixture) and 5-iminothianthrene 5,10,10-trioxide (9) and further de-iminated products were also formed respectively as minor products. The stereochemical considerations on the S_N reactions are described in view of the steric effect and ‘flip-flap’ motion of the thianthrene framework.     

Isomerizations of benzannelated C9H10 bicyclic systems into cyclononatetraenes. insight into the behaviour of medium-sized conjugated rings

Dibenzobicyclo[5.2.0]non-8-ene 9 was prepared from 2,3:6,7-dibenzocycloheptatriene as starting material. The bicyclic system 9 isomerized thermally to give cis,trans- and cis,cis-1,2:7,8-dibenzocyclononatetraene. The formation of cis,trans-1,2:7,8-dibenzocyclononatetraene occurs in an allowed concerted electrocyclic process of general interest.     

cis/trans-Isochromanones. DMAP induced cycloaddition of homophthalic anhydride and aldehydes

Homophthalic anhydride (1) reacts with wide variety of aromatic aldehydes, in the presence of chloroform and DMAP (N,N-dimethyl-4-amino-pyridine) at room temperature, to give in high yields cis- and trans-1-oxo-isochroman-4-carboxylic acids. Under these conditions, the trans-isomer is predominant and formation of Perkin-type products was not observed in contrast to the reaction carried out in the presence of pyridine. The unexpected trans-6-oxo-11-thiophen-2-yl-11,12-dihydro-6H-dibenzo[c,h]chromene-12-carboxylic acid methyl ester (8) was isolated when the reaction between 1 and thiophene-2-carbaldehyde was carried out in pyridine.     

Electrostatic forces that determine O,O-trans versus O,S-cis conformers in the aminated porphyrin complexes of Cd(N-NHCO-2-C4H3O-tpp)(OAc) and Cd(N-NHCO-2-C4H3S-tpp)(OAc)

Two new diamagnetic, mononuclear and aminated porphyrin complexes of O,O-trans-Cd (3-trans) and O,S-cis-Cd (4-cis) have been synthesized and characterized by ¹H, ¹³C NMR spectroscopy. The crystal structures of (acetato)(N-2-furancarboxamido-meso-tetraphenylporphyrinato)cadmium(II) [Cd(N-NHCO-2-C₄H₃O-tpp)(OAc); 3-trans] and (acetato)(N-2-thiophenecarboxamido-meso-tetraphenylporphyrinato)cadmium(II) [Cd(N-NHCO-2-C₄H₃S-tpp)(OAc); 4-cis] were determined. The coordination sphere around Cd²⁺ is a distorted square-based pyramid in which the apical site is occupied by a bidentate chelating OAc⁻ group for 3-trans and 4-cis. The plane of three pyrrole nitrogen atoms [i.e., N(1), N(2), N(4) for 3-trans and N(1), N(2), N(3) for 4-cis] strongly bonded to Cd²⁺ is adopted as a reference plane 3N. The N(3) and N(4) pyrrole rings bearing the 2-furancarboxamido (Fr) and 2-thiophenecarboxamido groups in 3-trans and 4-cis, respectively, deviate mostly from the 3N plane, thus orienting separately with a dihedral angle of 33.4° and of 31.0°. In 3-trans, Cd²⁺ and N(5) are located on different sides at 1.06 and −1.49 Å from its 3N plane, while in 4-cis, Cd²⁺ and N(5) are also located on different sides at 1.04 and −1.53 Å from its 3N plane. An attractive electrostatic interaction between the Cd²⁺ and O(4)⁻ atoms in furan stabilizes the O,O-trans conformer of 3. A repulsive electrostatic interaction between Cd²⁺ and S(1)⁺ destabilizes the O,S-trans conformer of 4. Both of these repulsive and the mutually attractive interactions between S(1)⁺ and O(3)⁻ atoms favor the O,S-cis rotamer of 4 both in the vapor phase and in low polarity solvents. NOE difference spectroscopy, HMQC and HMBC were employed for the unambiguous assignment of the ¹H and ¹³C NMR resonances of 3-trans and 4-cis in CDCl₃ at 20 and −50 °C.     

An improved synthesis of ethyl cis-5-iodo-trans-2-methylcyclohexanecarboxylate, a potent attractant for the Mediterranean fruit fly

Both racemic ethyl 5-iodo-2-methylcyclohexanecarboxylate (1), known as Mediterranean fruit fly attractant ceralure B₁, and its (−)-(1R,2R,5R) enantiomer 1a were conveniently synthesized from commercially available racemic trans-6-methyl-3-cyclohexenecarboxylic acid 2 or its (1R,6R) enantiomer 2a. Key steps included an asymmetric Diels-Alder reaction using a sultam auxiliary and cyclization of the unwanted trans-5-iodo-trans-2-methylcyclohexanecarboxylic acid (8) to the intermediate lactone 7 (or 8a to 7a). The new method may circumvent chromatographic separations and seems amenable to scale-up.     

The first asymmetric synthesis of all four isomers of cis- and trans-3,4-dihydroxy-3,4-dihydromollugin

Asymmetric synthesis of all the four stereoisomers of cis-3,4-dihydroxy-3,4-dihydromollugins 4 and 6 and trans-3,4-dihydroxy-3,4-dihydromollugins 5 and 7 was achieved. The O-methoxymethyl mollugin derivatives were dihydroxylated to (−)- and (+)-cis-3,4-dihydroxy-3,4-dihydromollugin derivatives using both AD-mix-α and AD-mix-β. Deprotection of the MOM-ethers of cis-dihydroxy compounds resulted in the targeted stereoisomers (−)-(3R,4R)-cis-3,4-dihydroxy-3,4-dihydromollugin 4, (−)-(3R,4S)-trans-3,4-dihydroxy-3,4-dihydromollugin 5, (+)-(3S,4S)-cis-3,4-dihydroxy-3,4-dihydromollugin 6 and (+)-(3S,4R)-trans-3,4-dihydroxy-3,4-dihydromollugin 7. These routes were paved with difficulties, for example, incompatibility of the substrates with AD-mixes, the unexpected formation of trans-dihydroxy compounds and failures in deprotection protocols.     

The oximation of cis-1-alkyl-3-5-diphenyl-piperidin-4-ones

The oximation of 1-alkyl-3,5-diphenyl-piperidin-4-ones in which the phenyl groups are in a cis (bis-equatorial) configuration, leads to oximes having a trans configuration, with the phenyl syn to the oximic OH-group, in an axial arrangement.Acid hydrolisis of the oximes affords about 90% of cis-1 and 10% of trans-2 1-alkyl-3,5-diphenyl-piperidin-4-ones.Ketones 1 and 2 in acid and in alkaline media, undergo equilibration through keto-enolic tautomerism.     

Synthesis of syn- and anti-tricyclo [4.1.0.02,4] heptan-5-ones and related compounds

A convenient entry to both title compounds 1 and 2, as well as to cis- and trans-4-iodomethyl-bicyclo [3.1.0]-hexan-2-ones 3and 4 and to 4-methyl-bicyclo [3.1.0]-hex-3-en-2-one 5 involving base-promoted reactions of cis- and -trans-3,4-diiodomethylcyclopentanones 6 and 7 is reported, and the behaviour of 6 and 7 towards different bases. bfv40bp4761b     

Heterobimetallic [Ru(II)/Fe(II)] complexes: On the formation of trans- and cis-[RuCl2(dppf)(diimines)]

The synthesis and characterization of trans/cis-[RuCl₂(dppf)(diimines)], dppf = 1,1′-bis(diphenylphosphino)ferrocene; diimines = 2,2′-bipyridine (trans/cis-(1)), the new complexes with 4,4′-dimethyl-2,2′-bipyridine (trans/cis-(2)) and 1,10-phenanthroline (cis-(3)) are presented. The complexes were synthesized using two routes and the trans/cis-isomer formation is dependent upon conditions and the precursor applied. The trans-isomer (kinetic) readily isomerizes to the cis-isomer (thermodynamic) when exposed to light (fluorescent) and this process was followed by cyclic voltammetry and UV-vis. The electrochemical studies on these complexes reveal that Fe^(III)/Fe^(II) couples are insensitive to the isomer (trans/cis) formed, but the Ru^(III)/Ru^(II) couples are dependent on the isomer. Transfer-hydrogenation reactions for reduction of acetophenone were conducted using complexes cis-(1) and cis-(2) and the results are compared with that obtained for similar complexes. X-ray structure for cis-(3) are presented and discussed.     

Stereoselective synthesis of highly substituted trans-2,3-dihydrofuran and trans-1,2-cyclopropane derivatives containing sulfonyl groups

trans-2,3-Dihydrofuran derivatives 3 and trans-1,2-cyclopropane derivatives 4 were prepared with high chemoselectivity and moderate overall chemical yield by the reaction of α,β-unsaturated sulfones 1 with arsonium bromides 2 in the presence of potassium carbonate. The structures of products obtained were identified by IR, MS, ¹H NMR, elemental analysis, and X-ray diffraction analysis.     

The synthesis of potential Neramexane metabolites: cis- and trans-3-amino-1,3,5,5-tetramethylcyclohexanecarboxylic acids

A seven step synthetic route toward potential Neramexane metabolites cis- and trans-3-amino-1,3,5,5-tetramethylcyclohexanecarboxylic acids, cis-1 and trans-1, has been developed from isophorone. The synthetic procedure represents a useful method for the preparation of γ-amino acids with both amino and carboxyl groups situated at tertiary carbon atoms.     

PhP-PPh group bound to 1,8-positions of naphthalene: Preparation of cis isomer and synthesis of binuclear complex

A thermodynamically less stable cis isomer of 1,2-diphosphacycle was prepared from the corresponding trans isomer. Diphosphine, in which a PhP-PPh bond bridges the 1,8-positions of naphthalene, 1,2-diphenyl-1,2-dihydronaphtho[1,8-cd][1,2]diphosphole (1), was first prepared according to a previously reported method, and the trans isomer of 1 was irradiated in tetrahydrofuran with UV-vis light to reach equilibrium with cis-1 in a trans:cis ratio of 1:2. When a similar photochemical conversion was carried out using a saturated hexane solution of trans-1, cis-1 was precipitated in a good yield of 94%. The configuration of cis-1 was confirmed by X-ray analysis. Both cis- and trans-1 diphosphine ligands were used for the preparation of binuclear gold complexes. The crystal structure of (μ-cis-1)-[AuCl]₂ demonstrated that the two lone pairs of cis-1 are suitably directed for arrangement of the two gold centers in close proximity to each other. The two independent (μ-cis-1)-[AuCl]₂ molecules in the crystal were found to form a dimer through the multiple intermolecular interaction among the gold centers.     

Thermal [2 + 2] cyclodimerisation of strained olefins. Cis,trans-1,5-cyclo-octadiene and trans-cyclo-octene

The title reaction in the absence of catalysts has been investigated both with the racemic and with the optically active cycloolefins. Both title olefins form [2 + 2] dimers of the trans double bonds with complete retention of configuration (trans-syn-trans2 by R + S and trans-anti-trans3 by R + R combination) and with mono-inversion (cis,trans4, both by R + S and R + R combinations), but almost none with di-inversion (cis-syn-cis5 and cis-anti-cis6), together with trans-cis isomerised starting olefins.     

An efficient chemoenzymatic method to prepare optically active primary-tertiary trans-cycloalkane-1,2-diamines

Optically active trans-N-Boc-cyclopentane- and cyclohexane-1,2-diamines (7) were prepared by a chemoenzymatic method from the corresponding (±)-trans-N,N-diallylcycloalkane-1,2-diamine. These mono-carbamates 7 (ee=99%) were used as the starting materials in the syntheses of different vicinal primary-tertiary diamines. Thus, by means of a simple three-step sequence involving a reductive-amination of an aromatic aldehyde with 7, N-methylation and finally, cleavage of the Boc group, several trans-N-(arylmethyl)-N-methylcyclopentane- and cyclohexane-1,2-diamines were obtained in high yields.