Aryl Carbene Complexes Research Articles

Alkyne Competition in the Benzannulation Reaction with Chromium Carbene Complexes

The benzannulation reaction of Fischer carbene complexes is investigated under conditions where the reaction of the carbene complex is occurring in the presence of two different alkynes. A series of competition experiments are examined where the effects of various structural factors are explored by pitting 10 different carbene complexes with 11 different alkynes. Terminal alkynes will react selectively over internal alkynes in all cases examined including both aryl and alkenyl complexes. Aryl carbene complexes with methoxy substituents do not give quite as high selectivity for terminal alkynes over internal alkynes ( approximately 95:5) as do isopropoxy substituents (>99:1), whereas most alkenyl complexes give high selectivity with both substituents (>99:1). Competition experiments between two different terminal alkynes or between two different internal alkynes did not result in anything more than very modest selectivities at best ( approximately 2:1). Excellent selectivities were realized between two different terminal acetylenes if one of the terminal acetylene was protected with a trimethylsilyl group. Finally, it was demonstrated that the high selectivities between terminal and internal alkynes can be utilized in the reaction with molecules that contain both types of alkyne functions.

ChemInform Abstract: Recent Advances in Selective Organic Synthesis Mediated by Transition Metal Complexes

This short review covers some useful synthetic transformations mediated by group 6 Fischer alkoxy carbene complexes. Alkenyl carbene complexes derived from (±)-8-phenylmenthol are suitable Michael acceptors towards organolithium reagents -alkyllithium and lithium enolate derivatives-yielding ultimately b-alkyl substituted aldehydes with 80±98% enantiomeric excess. The reaction of (menthyloxy)aryl carbene complexes with sBuLi and tBuLi resulted in clean dearomatization leading to 1,4-cyclohexadiene derivatives. If alkynyl lithium, instead of alkyllithium, compounds are reacted with aryl carbene complexes different products -furans, propargyl ethers, alkoxyindenes are selectively produced. Enamines derived from (S)-methoxymethylpyrrolidine and both aldehydes and ketones react with alkenyl carbenes to afford with very high selectivity [3‡2] cycloadducts which are elaborated into useful, enantiopure 3,4-disubstituted cyclopentanones and 2,3-disubstituted 2-cyclopentenones, respectively. The [4‡3] carbocyclization occurs from alkenyl carbene complexes and 2-aminobutadiene derivatives, while the analogous heterocyclization can be accomplished from various types of azabutadienes and both alkenyl and alkynyl derivatives. Ef®cient structural modi®cations of terpenes can be done using boroxycarbene complexes via C±H insertion reactions. Finally, representative examples of cyclopropanation of electronically neutral alkenes with Fischer carbene complexes are provided.

Reactions of Complex Ligands. Part 107 Densely Substituted Hydroquinoid Phenanthrene and Triphenylene Cr(CO)3 Complexes: Chromium‐Templated Synthesis and Molecular Structure

AbstractDensely substituted hydroquinoid phenanthrene (10–18), acephenanthrene (19), and triphenylene chromium tricarbonyl complexes (20–22) have been prepared via benzannulation of naphthalenyl (1–7), acenaphthenyl (8) and phenanthrenyl carbene complexes (9), respectively. The naphthalenyl, acenaphthenyl and phenanthrenyl carbene complexes 1–9 were obtained in 52–88 % yield starting from commercially available bromoarenes by dehalolithiation, addition of hexacarbonyl chromium to the lithioarene and O‐alkylation of the resulting acyl chromates with trimethyloxonium tetrafluoroborate (Fischer route). The benzannulation of the aryl carbene complexes (either with 3‐hexyne / (t‐butyl)dimethylsilyl chloride or with (t‐butyl)dimethylsilylethyne) allowed the regiospecific synthesis of the oligocyclic hydroquinoid arene tricarbonyl chromium complexes 10–22 in 44–94 % yield thus providing a two‐step synthesis with overall yields of 18 ‐ 80 %. Under the kinetic reaction conditions used the metal atom is exclusively coordinated to the persubstituted terminal hydroquinoid ring. The molecular structures of phenanthrene complexes 10, 12–14, and 16, acephenanthrene complex 19, and triphenylene complexes 20 and 21 in the solid state have been determined by X‐ray crystallography. The carbonyl ligands either adopt an eclipsed (10, 12, 14, 16, 19, 20) or staggered (13, 21) exo‐conformation pointing away from the center of the phenanthrene, acephenanthrene and triphenylene ligands, respectively. The coordination of the metal atom to the hydroquinoid ring is unsymmetric with the largest metal‐carbon distances found between the chromium atom and one bridgehead carbon and the ring carbon atom bearing the bulky (t‐butyl)dimethylsilyloxy (TBDMSO) substituent.

Mononuclear Biscarbene Complexes by Direct Nucleophile Addition to a CO Ligand of Fischer Arylcarbene Complexes

Adding up carbene ligands: The unusual addition of some nucleophiles to a CO ligand of Fischer aryl carbene complexes has been developed and represents a novel and efficient approach to achieve once again the CO ligand → carbene ligand conversion. The potential of this methodology for the stereoselective synthesis of electron-rich 1,3-dienes is presented (see scheme).

Syntheses, structures and reactivities of diindenyl-coordinated diiron bridging carbene complexes

Compound [Fe 2(μ-CO) 2(CO) 2(η 5-C 9H 7) 2] ( 1) reacts with aryllithium reagents, ArLi (Ar = C 6H 5, p-CH 3C 6H 4, p-CF 3C 6H 4) followed by alkylation with Et 3OBF 4 to give the diindenyl-coordinated diiron bridging alkoxycarbene complexes [Fe 2{μ-C(OC 2H 5)Ar}(μ-CO)(CO) 2(η 5-C 9H 7) 2] ( 2, Ar = C 6H 5; 3, Ar = p-CH 3C 6H 4, 4, Ar = p-CF 3C 6H 4). Complex 4 reacts with HBF 4 · Et 2O at low temperature to yield cationic bridging carbyne complex [Fe 2(μ-CC 6H 4CF 3- p)(μ-CO)(CO) 2(η 5-C 9H 7) 2]BF 4 ( 5). Cationic 5 reacts with NaBH 4 in THF at low temperature to afford diiron bridging arylcarbene complex [Fe 2{μ-C(H)C 6H 4CF 3- p}(μ-CO)(CO) 2(η 5-C 9H 7) 2] ( 6). The reaction of 5 with NaSC 6H 4CH 3- p under the similar conditions gave the bridging arylthiocarbene complex [Fe 2{μ-C(C 6H 4CF 3- p)SC 6H 4CH 3- p}(μ-CO)(CO) 2(η 5-C 9H 7) 2] ( 7). Complex 5 can also react with carbonylmetal anionic compounds Na[M(CO) 5(CN)] (M = Cr, Mo, W) to produce the diiron bridging aryl(penta-carbonylcyanometal)carbene complexes [Fe 2{μ-C(C 6H 4CF 3- p)NCM(CO) 5}(μ-CO)(CO) 2(η 5-C 9H 7) 2] ( 8, M = Cr; 9, M = Mo; 10, M = W). The structures of complexes 4, 6, 7, and 10 have been established by X-ray diffraction studies.

Novel dimetal bridging carbene complexes derived from a terminal carbonyl dimetal compound. Syntheses, structures and reactivities of 7H-indene-coordinated diiron bridging carbene complexes

Pentacarbonyl-7H-indenediiron, [Fe2(CO)5(eta3,eta5-C9H8)] (1), reacts with aryllithium, ArLi (Ar = C6H5, p-C6H5C6H4), followed by alkylation with Et3OBF4 to give novel 7H-indene-coordinated diiron bridging alkoxycarbene complexes [Fe2{mu-C(OC2H5)Ar}(CO)4(eta4,eta4-C9H8)] (2, Ar = C6H5; 3, Ar = p-C6H5C6H4). Complexes 2 and 3 react with HBF4.Et2O at low temperature to yield cationic bridging carbyne complexes [Fe2(mu-CAr)(CO)4(eta4,eta4-C9H8)]BF4 (4, Ar = C6H5; 5, Ar = p-C6H5C6H4). Cationic 4 and 5 react with NaBH4 in THF at low temperature to afford diiron bridging arylcarbene complexes [Fe2{mu-C(H)Ar}(CO)4(eta4,eta4-C9H8)] (6, Ar = C6H5; 7, Ar = p-C6H5C6H4). The similar reactions of 4 and 5 with NaSC6H4CH3-p produce the bridging arylthiocarbene complexes [Fe2{mu-C(Ar)SC6H4CH3-p}(CO)4(eta4,eta4-C9H8)] (8, Ar = C6H5; 9, Ar = p-C6H5C6H4). Cationic 4 and 5 can also react with anionic carbonylmetal compounds Na[M(CO)5(CN)] (M = Cr, Mo, W) to give the diiron bridging aryl(pentacarbonylcyanometal)carbene complexes [Fe2{mu-C(Ar)NCM(CO)5}(CO)4(eta4,eta4-C9H8)] (10, Ar = C6H5, M = Cr; 11, Ar = p-C6H5C6H4, M = Cr; 12, Ar = C6H5, M = Mo; 13, Ar = p-C6H5C6H4, M = Mo; 14, Ar = C6H5, M = W; 15, Ar = p-C6H5C6H4, M = W). Interestingly, in CH2Cl2 solution at room temperature complexes 10-15 were transformed into the isomerized 7H-indene-coordinated monoiron complexes [Fe(CO)2(eta5-C9H8)C(Ar)NCM(CO)5] (16, Ar = C6H5, M = Cr; 17, Ar = p-C6H5C6H4, M = Cr; 18, Ar = C6H5, M = Mo; 19, Ar = p-C6H5C6H4, M = Mo; 20, Ar = C6H5, M = W; 21, Ar = p-C6H5C6H4, M = W), while complex 3 was converted into a novel ring addition product [Fe2{C(OC2H5)C6H4C6H5-p-(eta2,eta5-C9H8)}(CO)5] (22) under the same conditions. The structures of complexes 2, 6, 8, 14, 18 and 22 have been established by X-ray diffraction studies.

Novel Reactions of Cyclooctatetraene (COT)-Coordinated Diiron Cationic Bridging Carbyne Complexes with Nucleophiles

The COT-coordinated diiron cationic bridging carbyne complexes [Fe2(μ-CAr)(CO)4(η8-C8H8)][BF4] (1, Ar = C6H5; 2, Ar = p-CH3C6H4; 3, Ar = p-CF3C6H4) were prepared by the reactions of the diiron bridging alkoxycarbene complexes [Fe2{μ-C(OC2H5)Ar}(CO)4(η8-C8H8)] with HBF4·Et2O at low temperature. Cationic 3 reacts with NaSR (R = C2H5, p-CH3C6H4) in THF at low temperature to afford diiron bridging sulfonylcarbene complexes [Fe2{μ-C(SO2R)C6H4CF3-p}(CO)4(η8-C8H8)] (7, R = C2H5; 8, R = p-CH3C6H4), while the reactions of 1−3 with NaBH4 under similar conditions gave diiron bridging arylcarbene complexes [Fe2{μ-C(H)Ar}(CO)4(η8-C8H8)] (9, Ar = C6H5; 10, Ar = p-CH3C6H4; 11, Ar = p-CF3C6H4). Complexes 1−3 can also react with anionic carbonylmetal compounds Na[M(CO)5(CN)] (4, M = Cr; 5, M = Mo; 6, M = W) to produce diiron bridging aryl(pentacarbonylcyanometal)carbene complexes [Fe2{μ-C(Ar)NCM(CO)5}(CO)4(η8-C8H8)] (12, Ar = C6H5, M = Cr; 13, Ar = p-CH3C6H4, M = Cr; 14, Ar = p-CF3C6H4, M = Cr; 15, Ar = C6H5, M = Mo; 16, Ar = p-CH3C6H4, M = Mo; 17, Ar = p-CF3C6H4, M = Mo; 18, Ar = C6H5, M = W; 19, Ar = p-CH3C6H4, M = W; 20, Ar = p-CF3C6H4, M = W). Unexpectedly, aniline and 2-naphthylamine react with cationic 1 and 3 to give novel COT-coordinated iron carbene complexes [Fe2{C(Ar)NHAr‘}(μ-CO)(CO)3(η8-C8H8)] (21, Ar = C6H5, Ar‘ = C6H5; 22, Ar = p-CF3C6H4, Ar‘ = C6H5; 23, Ar = p-CF3C6H4, Ar‘ = 2-naphthyl). In solution, products 21−23 were transformed into chelated iron carbene complexes [Fe2{C(Ar)NAr‘}(CO)4(η2:η3:η2-C8H9)] (24, Ar = C6H5, Ar‘ = C6H5; 25, Ar = p-CF3C6H4, Ar‘ = C6H5; 26, Ar = p-CF3C6H4, Ar‘ = 2-naphthyl) in high yields. The structures of complexes 7, 8, 11, 14, 15, 20, 22, and 24 have been established by X-ray diffraction studies.

Unusual reactions of cationic bridging carbyne complexes of dimethylsilane-bridged bis(η 5-cyclopentadienyl)diiron tricarbonyl with carbonylmetal anions

The reactions of the dimethylsilane-bridged cationic carbyne complexes of diiron, [Fe 2(μ-CO)(μ-CAr)(CO) 2{(η 5-C 5H 4) 2Si(CH 3) 2}]BBr 4 ( 1, Ar=C 6H 5; 2, Ar= p-CF 3C 6H 4), with carbonylmetal anionic compounds Na[M(CO) 5CN] ( 4, M=Cr; 5, M=Mo; 6, M=W) in THF at low temperature afford diiron bridging carbene complexes [Fe 2(μ-CO){μ-C(Ar)NCM(CO) 5}(CO) 2{(η 5-C 5H 4) 2Si(CH 3) 2}] ( 9, M=Cr, Ar=C 6H 5; 10, M=Mo, Ar=C 6H 5; 11, M=W, Ar=C 6H 5; 12, M=Cr, Ar= p-CF 3C 6H 4; 13, M=Mo, Ar= p-CF 3C 6H 4; 14, M=W, Ar= p-CF 3C 6H 4). In contrast to the reaction of 1 and 2, cationic carbyne complex [Fe 2(μ-CO)(μ-CC 6H 4CH 3- p)(CO) 2{(η 5-C 5H 4) 2Si(CH 3) 2}]BBr 4 ( 3) reacts with 4– 6 under the same conditions to produce novel cationic bridging carbyne complexes [Fe 2(μ-CO)(μ-CC 6H 4CH 3- p)(CO) 2{(η 5-C 5H 4) 2Si(CH 3) 2}] +[M(CO) 5CN] − ( 15, M=Cr; 16, M=Mo; 17, M=W). Analogous cationic bridging carbyne complex [Fe 2(μ-CO)(μ-CC 6H 4CH 3- p)(CO) 2{(η 5-C 5H 4) 2Si(CH 3) 2}] +[Fe(CO) 4CN] − ( 18) can also be obtained from the reaction of 3 with Na[Fe(CO) 4CN] ( 7). Complex 15 or 16 reacts with NaSR (R=CH 3, C 6H 5, p-CH 3C 6H 4) to give bridging mercaptocarbene complexes [Fe 2(μ-CO){μ-C(SR)C 6H 4CH 3- p}(CO) 2{(η 5-C 5H 4) 2Si(CH 3) 2}] ( 19, R=CH 3; 20, R=C 6H 5; 21, R= p-CH 3C 6H 4) in high yields. The related reaction of 1 with NaN(SiMe 3) 2 affords a novel benzonitrile-coordinated diiron complex [Fe 2(μ-CO) 2(CO)NCC 6H 5{(η 5-C 5H 4) 2Si(CH 3) 2}] ( 22). Unexpectedly, the reactions of 1 and 2 with 7 yield diiron bridging arylcarbene complexes [Fe 2(μ-CO){μ-C(H)Ar}(CO) 2{(η 5-C 5H 4) 2Si(CH 3) 2}] ( 23, Ar=C 6H 5; 24, Ar= p-CF 3C 6H 4). The products 23 and 24 and bridging p-tolyl-carbene complex [Fe 2(μ-CO){μ-C(H)C 6H 4CH 3- p}(CO) 2{(η 5-C 5H 4) 2Si(CH 3) 2}] ( 25) were also obtained from the reactions of 1– 3 with [(PPh 3) 2N][Cr(CO) 4NO] ( 8). The structures of 14, 15, 22, and 23 have been established by X-ray crystallography.

Reactivity of the inversely polarized phosphaalkenes RP=C(NMe2)2 (R = tBu, Me3Si, H) towards arylcarbene complexes [(CO)5M=C(oEt)Ar] (Ar= Ph, M = Cr, W; Ar = 2-MeC6H4, 2-MeOC6H4, M = W).

The reaction of the arylated Fischer carbene complexes [(CO)5M=C(OEt)Ar] (Ar=Ph; M = Cr, W; 2-MeC6H4; 2-MeOC6H; M = W) with the phosphaalkenes RP=C(NMe2), (R=tBu, SiMe3) afforded the novel phosphaalkene complexes [[RP=C(OEt)Ar]M(CO)5] in addition to the compounds [(RP=C(NMe2)2]M(CO)5]. Only in the case of the R = SiMe3 (E/Z) mixtures of the metathesis products were obtained. The bis(dimethylamino)methylene unit of the phosphaalkene precursor was incorporated in olefins of the type (Me2N)2C=C(OEt)(Ar). Treatment of [(CO)5W=C(OEt)(2-MeOC6H4)] with HP=C(NMe2)2 gave rise to the formation of an E/Z mixture of [[(Me2N)2CH-P=C(OEt)(2-MeOC6H4)]W(CO)5] the organophosphorus ligand of which formally results from a combination of the carbene ligand and the phosphanediyl [P-CH(NMe2)2]. The reactions reported here strongly depend on an inverse distribution of alpha-electron density in the phosphaalkene precursors (Pdelta Cdelta+), which renders these molecules powerfu] nucleophiles.

Versatile behaviour of iron–arylcarbene complexes towards alkoxides: CCl and CC bond activation reactions

The Cp-containing carbene complexes [ Fe(C 5 H 5 )(CO){κ 2(C,O)&0xF700; C(OMe)C 6 H 4-o -O Me}][OTf] ( 2) and [Fe(C 5H 5)(CO)(CH 3CN){C(OMe)C 6H 4- o-Cl}[OTf] ( 3) have been synthesised and characterised. Complex 2 has been characterised by a single-crystal X-ray diffraction analysis; the Fe–O distance of 2.045(5) Å suggests a rather strong bonding of the methoxy group. Substitution of one carbonyl ligand by PPh 3 allows the isolation of the chelate complex [ Fe(C 5 H 5 )(PPh 3){ κ 2(C,Cl)&0xF700; C(OMe)C 6 H 4-o -C l}][OTf] ( 4). The reaction of [ Fe(C 5 Me 5 )(CO){κ 2(C,Cl)&0xF700; C(OMe)C 6 H 4-o -C l}][OTf] ( 5) with alkoxides RONa (R=Me, Et) affords the chelate complexes [ Fe(C 5 Me 5 )(CO){κ 2(C,O)&0xF700; C 6 H 4-o -C(OMe)(O R)(OR)}] 7 (R=Me) and 8 (R=Et), respectively. Similarly, the reaction of 3 with EtONa affords [ Fe(C 5H 5)(CO){κ 2( C, O)−C 6H 4-o-C(O Et)(OEt)2}] ( 9), for which the ArCl bond has been cleaved. No activation of the ArCl bond is observed for the unchelated complex [Fe(C 5Me 5)(CO) 2{C(OMe)C 6H 4- o-Cl}][OTf]. In contrast, treatment of the anisyl derivative [ Fe(C 5 Me 5 )(CO){κ 2(C,O)&0xF700; C(OMe)C 6 H 4-o -O Me}][OTf] ( 6) with EtONa gives selectively the carbene complex [Fe(C 5Me 5)(CO)(C 6H 4- o-OMe){C(OEt) 2}] ( 12). The ArOMe bond remains intact, but cleavage of the CαCAr bond occurs. This rearrangement process, i.e. α-elimination of the anisyl substituent, is favoured by the lability of the ortho-OMe group. Treatment of 2 with NaOEt gives as the only identified compound the ethyl ester [MeOC 6H 4- o-(CO)OEt]. Clean formation of the methyl ester derivative [MeOC 6H 4- o-(CO)OMe] is observed upon oxidation of 2 with C 6H 5I +O −.

Reactions of Cationic Bridging Carbyne Complexes of Bis(η-cyclopentadienyl)diiron Tricarbonyl with Nucleophiles. A Route to Diiron Bridging Carbene Complexes

The reactions of the cationic carbyne complex of diiron, [Fe2(μ-CO)(μ-CPh)(CO)2(η-C5H5)2]BBr4 (3), with NaSMe, NaSEt, NaSPh, NaSC6H4Me-p, and NaSC6H4NO2-p in THF at low temperature afforded diiron bridging thiocarbene complexes [Fe2(μ-CO){μ-C(SR)Ph}(CO)2(η-C5H5)2] (5, R = Me; 6, R = Et; 7, R = Ph; 8, R = p-MeC6H4; 9, R = p-NO2C6H4). Complex [Fe2(μ-CO)(μ-CC6H4Me-p)(CO)2(η-C5H5)2]BBr4 (4) reacted similarly with NaSPh and NaSC6H4Me-p to give corresponding bridging carbene complexes [Fe2(μ-CO){μ-C(SR)C6H4Me-p}(CO)2-(η-C5H5)2] (10, R = Ph; 11, R = p-MeC6H4). Complex 3 also reacted with NaOPh and NaN(SiMe3)2 to yield bridging carbene complexes [Fe2(μ-CO){μ-C(OPh)Ph}(CO)2(η-C5H5)2] (12) and [Fe2(μ-CO){μ-C(N(SiMe3)2)Ph}(CO)2(η-C5H5)2] (13), respectively. Complexes 3 and 4 reacted with reactive salt [Et3NH][Fe2(μ-CO)(μ-SBun)(CO)6] to yield the bridging mercaptocarbene complex [Fe2(μ-CO){μ-C(SH)Ph}(CO)2(η-C5H5)2] (14) and the bridging butylthiocarbene complex [Fe2(μ-CO){μ-C(SBun)C6H4Me-p}(CO)2(η-C5H5)2] (15), respectively. The analogous reactions of [Et3NH][Fe2(μ-CO)(μ-SPh)(CO)6] with 3 and 4 afforded the thiolato-bridged iron carbonyl compound [Fe2(μ-SPh)2(CO)6] (16) and the bridging arylcarbene complexes [Fe2(μ-CO){μ-C(H)Ar}(CO)2(η-C5H5)2] (17, Ar = Ph; 18, Ar = p-MeC6H4), while [Et3NH][Fe2(μ-CO)(μ-SC6H4Me-p)(CO)6] reacted with 3 to yield 17 and [Fe2(μ-SC6H4Me-p)2(CO)6] (19). The reaction of metal carbonyl anion compounds Na2W(CO)5 and Na2Fe(CO)4 with 3 gave the same product, 17. The structures of 6, 7, 15, and 17 have been established by X-ray diffraction studies.

Acylamino Chromium Carbene Complexes: Direct Carbonyl Insertion, Formation of Münchnones, and Trapping with Dipolarophiles.

Acylamino Chromium Carbene Complexes: Direct Carbonyl Insertion, Formation of Münchnones, and Trapping with Dipolarophiles.

Recent advances in selective organic synthesis mediated by transition metal complexes

This short review covers some useful synthetic transformations mediated by group 6 Fischer alkoxy carbene complexes. Alkenyl carbene complexes derived from (±)-8-phenylmenthol are suitable Michael acceptors towards organolithium reagents -alkyllithium and lithium enolate derivatives-yielding ultimately b-alkyl substituted aldehydes with 80±98% enantiomeric excess. The reaction of (menthyloxy)aryl carbene complexes with sBuLi and tBuLi resulted in clean dearomatization leading to 1,4-cyclohexadiene derivatives. If alkynyl lithium, instead of alkyllithium, compounds are reacted with aryl carbene complexes different products -furans, propargyl ethers, alkoxyindenes are selectively produced. Enamines derived from (S)-methoxymethylpyrrolidine and both aldehydes and ketones react with alkenyl carbenes to afford with very high selectivity [3‡2] cycloadducts which are elaborated into useful, enantiopure 3,4-disubstituted cyclopentanones and 2,3-disubstituted 2-cyclopentenones, respectively. The [4‡3] carbocyclization occurs from alkenyl carbene complexes and 2-aminobutadiene derivatives, while the analogous heterocyclization can be accomplished from various types of azabutadienes and both alkenyl and alkynyl derivatives. Ef®cient structural modi®cations of terpenes can be done using boroxycarbene complexes via C±H insertion reactions. Finally, representative examples of cyclopropanation of electronically neutral alkenes with Fischer carbene complexes are provided.

Stereochemical Control of N,N-Disubstitution in Alkynylaminocarbene Complexes of Chromium(0) and Tungsten(0)

Stereocontrol in the introduction of substituents on the nitrogen of alkynylaminocarbene complexes can be achieved by a proper sequential aminolysis of the starting alkoxy carbene analogs followed by treatment of the resulting (E-alkylamino)carbene complex with Cs2CO3 in the presence of the desired electrophile. The use of Cs2CO3 as a base affords good yields of N,N-disubstituted alkynylcarbene complexes. The isomerization described for other systems was avoided in this case. The reaction is also applicable to bulky electrophiles like (−)-myrtenyl or (−)-perillyl bromides and also to arylcarbene complexes.

A new approach to hydrindenones by tautomer-arrested annulations of Fischer carbene complexes

The reactions of 2,6-disubstituted aryl carbene complexes with alkynes give hydrindenone products if a phenol function is present which prevents aromatization to an indene product by a tautomerization of a metal complexed vinyl alcohol intermediate.

Direct preparation of differentially protected hydroquinone-chromium(tricarbonyl) complexes from the benzannulation reaction of fischer carbene complexes

Methods for the preparation of differentially protected hydroquinone-chromium(tricarbonyl) complexes directly from alkenyl Fischer carbene complexes and alkynes are described. The benzannulation reaction of methoxy carbene complexes with alkynes produces hydroquinone chromium tricarbonyl complexes as their mono-methyl ethers which may be protected at the free aryl hydroxyl with either sequential or concurrent reaction with a variety of electrophiles, including silyl chlorides and triflates, acyl and alkyl halides, and anhydrides. The yields obtained for the arene complexes equal or exceed the yields for the phenol or quinone products isolated from the same benzannulation reactions in which the chromium tricarbonyl group has been oxidatively liberated from the arene. Differentially protected complexes can also be obtained directly from the reaction of β-silyl-alkenyl complexes with alkynes. These methods are not applicable to the preparation of differentially protected naphthohydroquinone chromium tricarbonyl complexes from the reaction of aryl carbene complexes with alkynes.

Cyclohexadienone annulations of aryl carbene complexes of chromium: new strategies for the synthesis of indole alkaloids

La reaction de composes acetyleniques avec des complexes carbonyles du chrome associes a des [methyl-1 indolyl-3 methoxy] methylenes fournit des dihydro carbazoles et une voie d'acces aux alcaloides de la famille de l'aspidosperma