ReviewTransition metals in organic synthesis: Highlights for the year 2003
Section snippets
General comments
This survey highlights the use of transition metals in organic synthesis for the year 2003. Comprehensive literature coverage with extensive citations is presented. The field of transition metal chemistry continued to expand in 2003 and have a significant role in functional group transformations and organic total synthesis. Some of the more standard applications have not been included in this review. Reactions of unusual substrates, new reaction conditions, and new catalyst systems have been
Carbon–carbon bond-forming reactions via transmetallation
Palladium-catalyzed cross-coupling reactions of organotin reagents (Stille couplings) with a large variety of electrophiles continued to be developed and extensively used in organic synthesis. The accelerating effect of added copper salts was studied using spectroscopic and kinetic methods [1]. A variety of palladium catalyst systems were described [2], [3], [4] including systems used in water [5], and reagents and reactants on solid support [6], [7]. Alkyl bromides having β-hydrogens were
Carbon–carbon bond-forming reactions using carbon nucleophiles
Palladium continued to dominate as the catalyst of choice for allylic alkylation reactions. Chloride ions were shown to have structural and kinetic effects on palladium-catalyzed allylic substitutions [810]. Regioselective allylic alkylations of silicon substituted substrates were described [811]. A silicon substituent on the central carbon of the η3-allyl complex was shown to stabilize the complex [812]. Allylic alkylation using allylic carbonates was found to be significantly slowed down in
Metal-catalyzed diazo decompositions (including other cyclopropanations)
Iron catalyzed the alkenylation of trifluoromethyl ketones using ethyl diazoacetate (Eq. (135)) [901]. An iron porphyrin complex catalyzed the alkenylation of ketones with ethyl diazoacetate [902]. Copper catalyzed the formation of 1,1-dibromo-1-alkenes by reaction of hydrazones with aldehydes and ketones in the presence of carbon tetrabromide (Eq. (136)) [903]. Rhodium catalyzed the decomposition of cyclic 2-diazo-1,3-dicarbonyl compounds in the presence of an acid halide to give β-acyloxy
Addition of C-nucleophiles to alkene and alkynes
Palladium catalyzed an oxidative coupling of organoboron reagents with alkenes using oxygen to reoxidize the catalyst [1002], [1003]. Palladium also catalyzed the oxidative coupling of triarylantimony reagents with terminal alkenes [1004] and indium catalyzed related reactions using organosilicon reagents [1005]. Palladium-catalyzed regioselective additions of organoboronic acids to allenes (Eq. (162)) [1006], [1007]. Rhodium-catalyzed related reactions of arylboranes [1008]. Palladium
Miscellaneous carbon–carbon bond-forming reactions
Cobalt catalyzed the cross-coupling of aromatic halides with allylic acetates [1174]. A palladium-catalyzed copper-mediated coupling of 2-nitro-1-halobenzenes with 2-halo-2-cycloalken-1-ones was described (Eq. (224)) [1175]. Palladium catalyzed the coupling of aromatic iodides with acetic anhydride to give aromatic methyl ketones (Eq. (225)) [1176]. Nickel catalyzed the homo-coupling of 2-chloro or 2-trifloxypyridines [1177], palladium catalyzed the homo-coupling of 1-iodoalkynes [1178],
Carbonylations of alkenes, allenes, and arenes
A palladium-catalyzed bis(methoxycarbonylation) of terminal alkenes was developed [1204]. Palladium catalyzed an asymmetric hydrocarbomethoxylation of styrene [1205]. Titanium mediated a hydrocarboxylation of alkynes using carbon dioxide to form α,β-unsaturated carboxylic acids. Further functionalization of the intermediately formed titanacylopropene with electrophiles was also reported (Eq. (229)) [1206].
A tandem rhodium-catalyzed alkene hydroformylation Fischer indole synthesis was described
Metathesis reactions
A large number of reports on ring-closing metathesis reactions using Grubbs’-type ruthenium catalysts were published. The rate and mechanism of ring-closing metathesis using ruthenium allylidene complexes were studied [1264]. New, highly efficient, and sometimes air stable, or recyclable ruthenium catalysts [1265], [1266], [1267], [1268], [1269], [1270], [1271], [1272] and reaction conditions [1273] were developed. Ruthenium byproducts were removed by sequential treatment with silica gel,
Cycloisomerizations
Reactions wherein all elements of the starting material were found in a cyclic product are grouped in this section. An intermolecular copper-catalyzed [2+2]cycloadditions was used in a synthesis of tricycloclavulone [1395]. Ruthenium catalyzed intermolecular [2+2]cycloadditions of bicyclic alkenes and chiral propargylic alcohols [1483], and of disubstituted alkynes [1484].
A gold catalyzed intramolecular Diels–Alder reaction aromatization sequence was used in synthesis of jungianol and
Miscellaneous isomerizations
Palladium catalyzed an enantioselective aza-Claisen rearrangement of allylic imidates [1542]. Copper catalyzed a sequential carbon–oxygen coupling-Claisen rearrangement (Eq. (311)) [1543]. Palladium catalyzed isomerization of alkenyl epoxides to 4-hydroxy-2-alkenoic acid esters [1544] or β,γ-unsaturated ketones depending on the substitution pattern [1545]. Palladium catalyzed a rearrangement of 2-allyloxypyridines to N-allyl-2-pyridones (Eq. (312)) [1546]. Palladium catalyzed the isomerization
Miscellaneous carbocyclizations
Palladium catalyzed benzannulation of alkynes with allylic substrates to give polyfunctionalized benzenes [1563]. Palladium catalyzed a cyclization–allylation of 1-hydroxy-2,3,4-pentatrienes in the presence of an allylic bromide (Eq. (321)) [1564]. Depending on the palladium catalyst, either 2-hydroxycyclopentenones or cross-conjugated cyclopentenones are obtained from 2-alkoxy-1,4-diene-3-ones (Eq. (322)) [1565]. Copper-catalyzed asymmetric cyclizations of dialkenyl ketones to form
Formation of carbon–halogen bonds
Alkenyl iodides were prepared by the chromium-mediated Takai olefination of aldehydes using iodoform [1589]. This reaction was used in the synthesis of annonaceous acetogenins [418], C21–C26 fragment of superstolide A [48], lasonolide [100], E type I phytoprostanes [1590], oxazolomycin antibiotics [80], disorazole A1 [439], and (E)- and (Z)-(+)-pinnatifidenyne (Eq. (337)) [444]. Tributyltindiiodomethane was also used to introduce an alkenyl stannane in a synthesis of isocembrene (Eq. (338))
Formation of carbon–nitrogen and –oxygen bonds from boron, and tin reagents
Copper catalyzed the amination of aryl boronic acids and esters with aziridines [711], α-amino esters [1595], N-heteroaromatic compounds [1325], [1596], 6H-pyrido[3,4-b]pyrazine-5-one [1597], and of aromatic boronic acids and trifluoroborates with amines [1598]. Copper mediated the N-9 arylation of purines using arylboronic acids [1599].
Copper catalyzed the coupling of phenols with aromatic boronic acids and esters to give diaryl ethers [1325], [1596]. An intramolecular copper-mediated reaction
Formation of epoxides
Vanadyl acetylacetonate-catalyzed epoxidations of allylic and in some cases homoallylic alcohols using peroxides continued to be an invaluable tool in organic total synthesis [122]. Synthetic targets include, phytuberin [1601], cyclopentenone protaglandins [1602], (−)-aphanorphine [1603], eleutherobin (Eq. (340)) [1604], Sch 49028 [1605], and (−)-herbertenediol [1606]. Asymmetric epoxidation of homoallylic alcohols using VO(OiPr)3 and a chiral ligand was employed in a synthesis of
Formation of heterocycles
Miscellaneous reactions forming heterocycles not included in the previous sections are discussed here. Palladium catalyzed the oxidative transformation of β-aminocyclopropanols to 2,3-dihydro-1H-pyridin-4-ones (Eq. (343)) [1622]. Palladium catalyzed the formation of a chiral oxazoline via intramolecular O-alkylation of a 3-acetoxy-4-N-benzoylamino-1-alkene in a synthesis of (+)-spectaline 2 [1623]. Palladium catalyzed an interesting formation of 3-azabicyclo[3.1.0]hexanes from 1,2,7-trienes and
Formation of carbon–hydrogen bonds
A variety of functional groups were replaced by a hydrogen atom using palladium-catalyzed methodologies. Palladium complexes, together with a hydride source, such as ammonium formates and triethylsilane, catalyzed the reduction triflates and halides. Synthetic applications include, (−)-blestriarene C [1653], lignans [1654], azaspiracid-1 (Eq. (365)) [65], 12-alkoxybenzo[c]phenanthridine bases [1655], 3-arylisocoumarins [82], fragranol and grandisol (Eq. (366)) [1656], merrilactone A [1430], and
Formation of carbon–oxygen double bonds
A number of synthetic applications of the Saegusa reaction were published, for example applications toward illudins [1663], gymnocin A [304], pleurotellol and pleurotellic acid (Eq. (370)) [1664], illudosin [1665], (−)-xialenone A [1666], and galubulima alkaloid GB 13 (Eq. (371)) [1667].
Titanium dioxide supported palladium nanoclusters were used in Wacker oxidations [1668]. Wacker-type oxidation, i.e., reaction of monosubstituted terminal alkenes with palladium(II) and water to afford methyl
Reactions of isolated transition metal complexes and titanium- and zirconium-intermediates
A number of transition metal-catalyzed reactions were published wherein metal complexes were allowed to react with one or more of the ligands without demetallation of the complex. The metal can then later be removed after serving as a template. Arene tricarbonyl chromium complexes continued to be extensively used as templates for organic reactions. Selective functionalization of a tetralkylbenzene complex was described (Eq. (377)) [1680]. Diastereoselective additions of organozinc reagent to
Miscellaneous reactions
Cobalt catalyzed a three-component coupling between an aromatic aldehyde and 1,3-dicarbonyl compound, and a nitrile to give β-acetamido carbonyl compounds (Eq. (412)) [1734]. Nickel catalyzed a coupling of alkynes, imines and organoboron reagents to give allylic amines (Eq. (413)) [1735]. A three-component palladium-catalyzed coupling of arylethylidene malonitriles, allylic chlorides, and allenylstannanes to give 1,7-enynes was described (Eq. (414)) [1736]. A palladium–copper catalyst system
Reviews
The following reviews appeared in 2003:
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Transposition of allylic alcohols into carbonyl compounds mediated by transition metal complexes [1759].
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Rhodium-catalyzed carbon–carbon bond-forming reactions of organometallic compounds [1760].
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Palladium-assisted routes to nucleosides [1761].
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Palladium-catalyzed alkynylations [1762].
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Asymmetric hydroalkenylation reaction [1763].
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Catalytic enantioselective CH activation by means of metal-carbenoid-induced CH insertion [1764].
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Asymmetric transition
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