Vinyl Carbene Research Articles

Optically active naphthohydroquinone and naphthoquinone tricarbonyl chromium complexes via diastereoselective benzannulation with sec. alcohol auxiliaries

The asymmetric benzannulation of optically active aryl or vinyl (alkoxy)carbene chromium complexes bearing chiral sec. alcohol auxiliaries with 3,3-dimethyl-1-butyne proceeds with moderate to high diastereoselectivities. The best results are obtained with (−)- and (+)-menthol derivatives. The stereoselectivity depends on the unsaturated carbene substituent and the solvent used. Enantiopure S-5-10- η 6-tricarbonyl-(2- tert.-butyl-1,4-naphthoquinone)chromium 25 was synthesized by intramolecular haptotropic migration of the tricarbonyl chromium fragment within the benzannulation product followed by deprotection and oxidation.

Patchouli Fragrance Chemistry: Stereoselective Synthesis of (±)-ISO-Norpatchoulenol

Abstract A short and efficient stereoselective synthesis of (±)-iso-norpatchoulenol 3 involving, as a key step, the intramolecular trapping of a vinyl carbanion is described. The new compound has a weak characteristic odor of patchouli.

Selective organic synthesis via group 6 metal carbene complexes

Abstract

Generation and trapping of 1,3-dithian-2-ylidene-substituted ethyl carbene. On the existence of 4,8-dithiaspiro[2.5]oct-1-ene

The readily available sodium salt of 2-(1,3-dithian-2-ylidene)acetaldehyde tosylhydrazone 6 could be thermolysed to transient 2-(2-diazoethylidene)-1,3-dithiane 7 and from there to 1,3-dithian-2-ylidene-substituted ethyl carbene 8. Both species gave cycloadditions with different types of alkenes. Evidence is presented for the electrocyclisation of the vinyl carbene to 4,8-dithiaspiro[2.5]oct-1-ene.

Photoaddition of Alkenes to Conjugated α-Diketones: Tandem Cyclizations Leading to Tetrasubstituted Furans1a

Photocycloaddition of 9a−c with 2 leads cleanly to tetrasubstituted furans 12a−c, respectively, in yields of ∼85%. The reactive triplet is efficiently sensitized by 2-benzoylnaphthalene and quenched by anthracene, indicating that ET is in the range 43−58 kcal/mol. A mechanism is proposed involving an alkyl propargyl biradical (as 10) that closes first to a vinyl carbene (as 11) and then to product. Reaction of 9c with 20 furnishes only 22, and this result rules out an alternative mechanism in which the order of steps leading to the carbene is reversed.

Cycloaromatization of Methyl (E)-4-(Methyllithio)-3-(1-pyrrolidinyl)-2-butenoate with α-Oxoketene N,S-Acetals: Direct Synthesis of 3,5-Bis(cycloalkylamino)biphenyls

The vinyl carbanion 2 undergoes cycloaromatization with α-oxoketene N,S-acetals 3 through 1,4-conjugate addition-elimination process to afford 3,5-diaminobiphenyls 4 in good yields.

Rapid synthesis of functionalized, alkoxy-substituted, allylstannanes from carbene complexes

Hydrostannation of readily available chromium and tungsten vinyl carbene complexes with tributyltin hydride provides a facile synthesis of highly substituted alkoxy-substituted allylstannanes. Preparation of acetal, keto, methoxy, and silyl substituted stannane reagents is demonstrated.

ChemInform Abstract: Synthons for the Parent Vinyl Carbene Complex in the Benzannulation Reaction.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthons for the Parent Vinyl Carbene Complex in the Benzannulation Reaction

The benzannulation reaction of Fischer carbene complexes with alkynes to produce phenols was found not be synthetically useful for the parent vinyl carbene complex 6a. The β-silylated vinyl carbene complex 6c is more stable than the parent vinyl complex 6a and can be effectively used as a synthon for 6a since during the benzannulation the silicon migrates to the phenol function preferentially over hydrogen to give the arene chromium tricarbonyl complexes of the type 19. This reaction is general for a number of alkynes that have incorporated important functionality and is more useful for terminal alkynes than for internal alkynes. The migration of the silicon is responsible for the fact that stable arene chromium tricarbonyl complexes can be isolated from these reactions and makes possible transformations that take advantage of the activating ability of the chromium tricarbonyl group. This is demonstrated in intramolecular aromatic nucleophilic additions reactions. It is also shown in a single example that the α-silylated vinyl carbene complex 10b can in principle also serve as a synthon for the parent vinyl carbene complex 6a, since the benzannulated product can be disilylated with trifluoroacetic acid

Diversity in the reaction modes of anionic and cationic stannyl reagents: γ-Chloro allylstannanes as a vinyl carbene equivalent, and its application for (±) -bakuchiol synthesis

Diversity in the reaction modes of anionic stannyl reagents is demonstrated by synthon representation. A new cationic stannyl reagent, γ-chloro allylstannane, has been developed as a vinyl carbene equivalent, and its utility is demonstrated by (±)-bakuchiol synthesis.

Synthetic Chemistry of Cyclopropenone Acetals. Penitricin and Buckminsterfullerene.

A variety of substituted cyclopropenone acetals have been prepared and studied for the purpose of gaining further insights into their organometallic and thermal chemistry. Acidic hydrolysis of the acetals gave the corresponding cyclopropenones, among these are a naturally occurring cyclopropenone antibiotic, penitricin. A new class of cysteine protease inhibitor can be realized if the penitricin moiety is contrived as a dipeptide-like binding site. Thermolysisbf substituted cyclopropenone acetals generates vinyl carbene species that undergo [1 + 2] and [3 + 2] cycloadditions to electrondeficient olefins. The cyclopropenone acetal also serves as a precursor to a dipolar trimethylenemethane. The vinyl carbene and the trimethylenemethane species undergo cycloaddition to give buckminsterfullerenes, with which the various organic derivatives of fullerenes generated have been shown to exhibit photo-induced cytotoxicity, DNA cutting activity and enzyme inhibition.

Generation and solution-phase behaviour of some 2-halogeno-1,3-ring-fused cyclopropenes

The title cyclopropenes 2b are readily formed by reaction of ring-fused β-silylated-gem-dihalogenocyclopropanes of the general type 1b with tetrabutylammonium fluoride in tetrahydrofuran solution. Those halogenocyclopropenes 2b which are fused to a seven- or eight-membered ring can be trapped with a range of 1,3-dienes and the corresponding Diels–Alder adducts 3b are produced in high yield. In contrast, those chlorocyclopropenes which are fused to a five- or six-membered ring cannot be trapped efficiently by added diene because they each undergo rapid rearrangement to an isomeric vinyl carbene. Thus, 6-chlorobicyclo[3.1.0]hex- 1(6)-ene 27 undergoes ring-expansion to carbene 28 which either inserts into the α-C–H bond of the reaction solvent tetrahydrofuran or adds to one of the double bonds of furan. In contrast, the carbene, 32, derived by ring-cleavage of 7-chlorobicyclo[4.1.0]hept-1(7)-ene 31 reacts with chloride ion to give, after protonation, (E)-2-chloro-1-(chloromethylene)cyclohexane 34. This latter result is at variance with an earlier claim that when the cyclopropene 31 is generated under vacuum gas-solid reaction conditions it rearranges, via a ring-expanded vinyl carbene 36, to 2-chlorocyclohepta-1,3-diene 37. In the present work it has been established that this claim is incorrect. X-Ray crystallographic analyses of (1′α,3′α)-(E)-3′-chloro-2′-(chloromethylene)cycloheptyl p-nitrobenzoate 54 and (1′R,2prime;S,3′S,8′S,9′S,10′S)-9′-chloro-137prime;-oxatetracyclo[8.2.1.02′.8′.02′.9′]tridec-11′-en-3′-yl p-nitrobenzoate 67 have been carried out.

Spiro fused β-lactam cyclopropenes

Δ3-1,3,4-Oxadiazolines (1) that share their C2 with C4 of a β-lactam ring in a spiro fusion were prepared. The structures were established through single crystal X-ray diffraction of 1a and by infrared, 1H, and 13C nuclear magnetic resonance spectroscopies. Thermolysis of 1 at 100 °C, in benzene containing dimethyl acetylenedicarboxylate, afforded spiro-fused β-lactam cyclopropene 12 in 33% yield. Similar thermolysis of 1b in the presence of ethyl phenylpropiolate gave spiro-fused β-lactam cyclopropene 13 (32%). The molecular structure of 12, determined by single crystal X-ray diffraction, has the two ester carbonyl carbons out of the plane of the cyclopropene ring by about 0.17 Ǻ, indicating substantial nonbonded steric interactions and suggesting unusually high strain energy. At 154.5 °C, 12 underwent isomerization to 19, presumably through a vinyl carbene intermediate.

Catalytic activity of a well-defined binuclear ruthenium alkylidene complex

The reaction of [Cp[sup *]RuCl][sub 4] with 1,1-diphenylcyclopropene (1) gives the bridging vinyl carbene complex [Cp[sup *]RuCl][sub 2][double bond]CHCH[double bond]CPh[sub 2] (4) in moderate yield. This material selectivity catalyzes the dimerization of 1 to the triene Ph[sub 2]C[double bond]CHCH[double bond]CHCH[double bond]CPh[sub 2]. Complex 4 polymerizes norbornene by a ring-opening metathesis process despite the bridging nature of the alkylidene. 13 refs., 1 fig.

Sterically congested molecules. 5. Trimeric [.alpha.-(1,1,3,3-tetramethyl-2-indanylidene)benzyl]lithium: structural example of an unsolvated vinyllithium derivative

The X-ray structure of this compound discloses the stabilization of a vinylic carbanion by two lithium cations in a hydrocarbon milieu. Each lithium cation is in turn coordinated to two carbanion centers and additionally to one aromatic CC bond as well as to one CH bond of a methyl group. These bonding interactions result in an unsolvated trimer with pseudo-C 3 symmetry.

Clusters containing ynamine ligands. 6. Transformations of an ynamine ligand in a dirhenium complex. Synthesis and structural characterization of Re2(CO)8[.mu.-H2CCHCNMe2], Re2(CO)7[.mu.-H2CCCNMe2](.mu.-H), and Re2(CO)8[.mu.-H2C:CCNMe2](.mu.-H)

The complex Re{sub 2}(CO){sub 8}({mu}-MeC{sub 2}NMe{sub 2}) (1) was transformed into three new compounds, Re{sub 2}(CO){sub 7}({mu}-{eta}{sup 3}-H{sub 2}CCCNMe{sub 2})({mu}-H) (2; 17%), Re{sub 2}(CO){sub 8}({mu}-H{sub 2}CCHCNMe{sub 2}) (3; 25%), and Re{sub 2}(CO){sub 8}({mu}-H{sub 2}C{double_bond}CCNMe{sub 2})({mu}-H) (4; 0.5%), when heated to 80 {degrees}C for 2 h. Compounds 2-4 were characterized by IR, {sup 1}H NMR, and single-crystal X-ray diffraction analyses. Compound 2 is a hydride-containing decarbonylation product of 1 formed by a shift of one of the hydrogen atoms on the C-methyl group to the metal atoms. It also contains a {eta}{sup 3} bridging (dimethylamino)allenyl ligand that exhibits carbene-like character at the amine-substituted carbon atom. Compounds 3 and 4 are isomers of 1 formed by a shift of one of the hydrogen atoms on the C-methyl group of 1 to one of the alkynyl carbon atoms. Compound 3 contains a bridging vinyl(dimethylamino)carbene ligand in which the vinyl group is {pi}-bonded to one metal atom and the carbene is terminally coordinated to the other metal atom. Compound 4 contains a {eta}{sup 2} bridging (dimethylamino)allenyl ligand in an unusual coordination in which the two coordinated carbon atoms lie parallel to the metal-metal bond. The amine-substituted carbon shows a pronounced carbene-like character. Addition ofmore » CO to 2 at 25{degrees}C/1atm yielded compound 4 (79%) and only a trace 3 (1%). At 75 {degrees}C 4 was slowly converted to 3 (54% n 18 h) and the new compound 5 (39% in 18 h). 16 refs., 3 figs., 14 tabs.« less

ChemInform Abstract: Functionally Substituted Vinyl Carbanions. Part 44. Synthesis of Odd‐ Numbered 13‐Crown‐4 Derivatives Possessing a Functional Group and Their Application in C‐Lithiation of Acrylates.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Functionally substituted vinyl carbanions, 44. Synthesis of odd‐numbered 13‐crown‐4 derivatives possessing a functional group and their application in C‐lithiation of acrylates

AbstractThe synthesis of symmetrically hydroxy‐substituted 13‐crown‐ 4 derivatives 2 and 3 is reported. To this end, diol 7 is first deprotonated with potassium tert‐butoxide and then treated with ditosylate 6 in the presence of lithium perchlorate as a template. Base‐catalyzed addition of 2 and 3 to methyl propiolate affords β‐alkoxy‐substituted acrylates 1a and 1b, respectively. Treatment of 1a with LDA in THF generates the β‐C‐lithiated species 1a‐A as indicated by quenching with CH3OD and reaction with propanal; thus, β‐deutero derivative 1a‐(β‐D) and tetronate 4a, respectively, are obtained. Competition experiments between 1a and methyl β‐methoxyacrylate (1c) with LDA in THF exhibit for 1a a higher thermodynamic but practically the same kinetic acidity.

Functionally substituted vinyl carbanions, 43. Convenient transformation of hexopyranosides into α‐methylene δ‐lactone derivatives

AbstractTreatment of glycopyranosyl phenyl sulfoxides 2ah, 1, 2bh, 1 with two equivalents of lithium diisopropylamide provides directly the C‐2‐lithiated glycal intermediates 3aAh, 1, 3bAh, 1 which, on reaction with formaldehyde as electrophile, furnish the 2‐hydroxymethyl derivatives 4ah, 1 and 4bh, 1, respectively. These compounds are transformed at elevated temperature and by acid catalysis directly into the α‐methylene‐δ‐lactones 5a, b. Correspondingly, from 2ah, 1 and methyl chloroformate as electrophile the 2‐methoxycarbonyl derivatives 6h and 61, respectively, are obtained. Treatment of 6h, 1 with Raney nickel leads to 2‐methoxycarbonyl‐substituted glycal 7 containing a β‐alkoxyacrylate moiety which again can be directly β‐C‐lithiated as demonstrated by the introduction of deuterium at C‐1.

Synthesis and thermolysis of tetrasubstituted cyclopropenes

Photolysis of 5-benzyl-2-methoxy-2,5-dimethyl-Δ3-1, 3,4-oxadiazoline and of the 5,5-dibenzyl analogue with 300-nm light afforded 1-phenyl-2-diazopropane and 1,3-diphenyl-2-diazopropane, respectively. The diazoalkanes were intercepted, in situ, with dimethyl acetylenedicarboxylate to afford 3-benzyl-4,5-bis(methoxycarbonyl)-3-methyl-3H-pyrazole and 3,3-dibenzyl-4,5-bis(methoxycarbonyl)-3H-pyrazole, respectively. Those pyrazoles are short-lived under the reaction conditions and undergo two major reactions. Photolysis prior to rearrangement affords the corresponding 3,3-dialkyI-1,2-bis(methoxycarbonyl)-cyclopropenes. Thermal 1,5-benzyl migration converts the two 3H-pyrazoles in part into the corresponding 4H-pyrazoles, which undergo photolysis to 2,3-dialkyl-1,3-bis(methoxycarbonyl)cyclopropenes. Thermolysis of the 3,3-dialkyl-1,2-bis(methoxycarbonyl) cyclopropenes affords conjugated dienes, presumably through the sequence cyclopropene → vinyl carbene → diene. The stereochemistry of the dienes was determined and a mechanism consistent with that stereochemistry is proposed. The 2,3-dialkyl-1,3-bis(methoxycarbonyl)cyclopropanes are very stable under conditions that convert isomeric 3,3-dialkyl-1,2-bis(methoxycarbonyl)cyclopropenes to conjugated dienes. It is proposed that the effect of substitution pattern on the thermolysis rate constants is the result of combined ground state and transition state factors.