4-Oxo-2-cyclopentenyl Acetate?A Synthetic Intermediate

An Enantioselective Approach to 4-O-Protected-2-cyclopentene-l,4-diol Derivatives via a Rhodium-Catalyzed Redox-Isomerization Reaction

Kinetic resolution of a series of cyclopentene-1,4-diol derivatives has been successfully achieved with enantiomeric excess up to 99.4% and a kf/ks ratio of 55 by a rhodium-catalyzed redox-isomerization reaction in a noncoordinating solvent.

Ligand-controlled selectivity in the desymmetrization of meso cyclopenten-1,4-diols via rhodium(I)-catalyzed addition of arylboronic acids

A highly enantioselective desymmetrization of meso cyclopent-2-ene-1,4-diethyl dicarbonates has been developed using a Rh-catalyzed asymmetric allylic substitution. Depending on the type of ligand used, each of two regioisomeric products can be obtained in good yield and excellent enantioselectivity. Under rhodium(I) catalysis, bisphosphine P-Phos ligands form trans-1,2-arylcyclopentenols as the major product, whereas Segphos ligands lead predominantly to trans-1,4-arylcyclopentenols.

Seebach's conjunctive reagent enables double cyclizations

When ketones flanked on both sides by nucleophilic atoms react with Seebach's nitropropenyl pivaloate reagent, direct couplings take place to give two new ring systems and three bonds. Cis-ring fusions are observed in unions leading to 5,5-, 5,6-, and 6,6-bicycles. Densely functionalized and rigid frameworks may be rapidly formed by the chemistry described herein.

Enantioselective Synthesis of Pentacycloanammoxic Acid

A highly effective enantioselective synthesis of pentacycloanammoxic acid (1), an unusual naturally occurring fatty acid from Candidatus Brocadia anammoxidans, has been accomplished. The C20-structure of 1 was assembled with stereocontrol from four building blocks, cyclobutene, 2-cyclopentenone, the chiral silylcyclopentenone 6, and 7-bromoheptanoic acid. Both 1 and its enantiomer are now available in quantities that should facilitate future studies on the mode of biosynthesis which appears to be unprecedented.

A Phosphine-Catalyzed [3+6] Annulation Reaction of Modified Allylic Compounds and Tropone

A novel phosphine-catalyzed reaction of modified allylic compounds, including acetates, bromides, chlorides, or tert-butyl carbonates derived from the Morita-Baylis-Hillman (MBH) reaction with tropone to yield [3+6] annulation products in excellent yields was developed. It offers a simple and convenient method for constructing bridged nine-membered carbocycles.

The Phane Properties of anti-[2.2](1,4)Biphenylenophane

[structure: see text] Anti-[2.2](1,4)biphenylenophane (4) was synthesized from de Meijere's tetrabromo[2.2]paracyclophane (5) through a four-step reaction sequence. Although an average separation of 3.09 A between the inner ring of the biphenylene units is normal for [2.2]paracyclophanes, a bond distance of 1.54 Afor the ethano C-C bridge at room temperature is shorter than usual. In addition, trimethylsilyl-substituted anti-[2.2](1,4)biphenylenophane 8 sublimes at 220 degrees C under a pressure lower than 1 x10(-5) Torr without decomposition or thermal isomerization. The high thermal stability of 8 suggested that the ethano bridges of the biphenylenophanes are less strained than those of [2.2]paracyclophane. Bathochromic shifts are observed in their UV-vis absorption spectra. The phane state interactions of 4 and 8 were evidenced by the weak structureless fluorescent emission maximized at 537 and 550 nm in CH(2)Cl(2) along with longer relaxation lifetimes of 229 and 292 ps, respectively.

Stereoselectivity Control in the Rh(I)-Catalyzed Conjugate Additions of Aryl and Alkenylboronic Acids to Unprotected Hydroxycyclopentenones

[reaction: see text] The stereoselective Rh(I)-catalyzed conjugate addition reaction of aryl and alkenylboronic acids to unprotected 2-phenyl-4-hydroxycyclopentenone is presented. The free OH group on the substrate is responsible for the stereochemistry, which is cis for arylboronic derivatives. In the case of the alkenylboronic compounds, the stereochemistry can be tuned to either a cis (bases as additives) or trans addition (CsF as additive) without the need of protecting groups.

Chemoenzymatic Asymmetric Total Synthesis of Phosphodiesterase Inhibitors: Preparation of a Polycyclic Pyrazolo[3,4-d]pyrimidine from an Acylnitroso Diels−Alder Cycloadduct-Derived Aminocyclopentenol

[reaction: see text] Enzymatic resolution of Boc-protected 4-aminocyclopenten-1-ol 4c gave both enantiomers 5c and 6c in high ee. Boc removal and separate condensation with chloropyrazolopyrimidine 18 provided elaborated 1,4-aminocyclopentenol derivatives 20 and 26, respectively. Separate treatment of 20 and 26 with Pd(0) under basic conditions induced cyclization to unsaturated polycycles 22 and 27, which, upon catalytic hydrogenation, were transformed to new cyclopentane-containing pyrazolopyrimidines 24 and 28, analogues of recently described novel phosphodiesterase inhibitors.

Azadiene Diels−Alder Cycloaddition of Fulvenes: A Facile Approach to the [1]Pyrindine System

[reaction: see text] Regioselective and stereoselective inverse-electron-demand Diels-Alder reaction of N-sulfonyl-1-aza-1,3-butadiene with fulvenes are described. The methodology provides an efficient and novel route to tetrahydro-[1]pyrindine systems.

Hetero [6+3] cycloaddition of fulvenes with N-alkylidene glycine esters: a facile synthesis of the delavayine and incarvillateine framework

[reaction: see text] In contrast to the [3+2] or [4+3] cycloaddition of N-metalated azomethine ylides and various alkenes, N-benzylidene glycine ethyl ester reacts with fulvenes to give the hetero [6+3] cycloaddition adducts with high stereoselectivity, constituting an efficient and novel route to [2]pyrindines.

A new method for installation of aryl and alkenyl groups onto a cyclopentene ring and synthesis of prostaglandins

To construct a new strategy for synthesis of cyclopentanoids, the transition metal-catalyzed coupling reaction of cis 4-cyclopentene-1,3-diol monoacetate 1 with hard nucleophiles, R(T)-m, was investigated (eq 1 in Chart 1). Although preliminary experiments using PhZnCl, PhSnMe(3), [Ph-B(Me)(OCH(Me)CH(Me)O)]-Li(+) (6a) (derived from boronate ester 4a (R(T) = Ph) and MeLi) in the presence of a palladium or a nickel catalyst resulted in production of unidentified compounds, enone 16, and/or ketone 17 or recovery of 1, a new borate 5a (derived from 4a and n-BuLi) in the presence of a nickel catalyst (NiCl(2)(PPh(3))(2)) in THF at room temperature furnished the trans coupling products 2a (R(T) = Ph) and 3a (R(T) = Ph) in high combined yield, but with a low product ratio of 0.9:1. The ratio was improved to 13:1 by addition of t-BuCN and NaI into the reaction mixture. This is the first successful example of the reaction of 1 with a hard nucleophile, and the increase in the ratio, realized with the additives, is unprecedented. This reagent system (borate 5 (1.2-1.8 equiv), NiCl(2)(PPh(3))(2) (5-10 mol %), t-BuCN (2-5 equiv), NaI (0.5-1 equiv), THF, room temp) was further investigated with aryl borates 5b-g and alkenyl borates 5h-n to afford 2b-n in moderate to good yields (52-89%) with practically acceptable levels of the regioselectivity (5 approximately 21:1), thus establishing the generality of the reaction (Table 2, eqs 6 and 7). Starting with the products of the coupling reaction, syntheses of the prostaglandin intermediates 13 and 14 (for 11-deoxy-PGE(2) and PGA(2)) and Delta(7)-PGA(1) methyl ester (15) were accomplished efficiently. During these investigations, LDA, LiCA, and LHMDS were found to be equally efficient bases for aldol reaction at the alpha' (alpha prime) position of cyclopentenones 39, 40, and 41 (Table 3).

Asymmetric synthesis of 1,2,3-trisubstituted cyclopentanes and cyclohexanes as key components of substance p antagonists

An efficient asymmetric synthesis of 1,2,3-trisubstituted cyclopentanes and cyclohexanes is described. Three methods were developed for the preparation of the 2,3-disubstituted cyclopentenones and cyclohexenones, which are key achiral building blocks. These intermediates are reduced catalytically with (R)-2-methyloxazaborolidine in high yield (82-98%) and excellent ee (89-96%). Directed reduction of the chiral allylic alcohols using Red-Al gives exclusively the 1,2-anti stereochemistry (>99:1). Epimerization of the ester center followed by saponification/crystallization affords the desired hydroxyacids in good yield (65-70%) and in high enantiomeric excess (>99%).

Silicon-tethered cyclocarbonylation of alkynes

[reaction: see text] Temporary union of alkynes in the Fe(CO)5-promoted cyclocarbonylation provides a method for carbonylative cross-coupling of alkynes to construct unsymmetrically substituted cyclopentadienones.

The [2 + 1] and [4 + 3] cyclization reactions of fulvenes with Fischer carbene complexes: new access to annulated cyclopentanones

Pentafulvenes are regioselectively cyclopropanated with group 6 Fischer carbene complexes leading to the homofulvene ring with complete endo selectivity. The homofulvene adducts undergo in turn a further cyclopropanation with ethyl diazoacetate or cyclopentannulation with a Fischer alkenyl carbene complex to provide substituted cyclopentanones after ozonolysis of the exocyclic carbon=carbon double bond. Fischer alkynyl carbene complexes also produce the corresponding alkynyl homofulvenes, albeit the exo stereoisomer is in this case exclusively or preferentially formed. Under moderate CO pressure, tungsten alkynyl carbene complexes cycloadd to pentafulvenes in a [4 + 3] fashion, giving rise to bicyclo[3.2.1]octadien-2-ones.

Scope and limitation of organocuprates, and copper or nickel catalyst-modified Grignard reagents for installation of an alkyl group onto cis-4-cyclopentene-1,3-diol monoacetate

Alkylation of the title compound 1 was investigated with two types of reagents. One is a copper reagent derived from R(T)MgX (X = Cl, Br) and CuX (X = CN, I) and the other is R(T)MgX in the presence of a copper or a nickel catalyst. First, butylation was studied with BuCu(CN)(MgX), Bu(2)Cu(CN)(MgX)(2), BuMgX/CuCN (10 mol %), BuCu (derived from BuMgCl and CuI), and BuMgCl/CuI (10 mol %) in THF or Et(2)O. We found that trans 1,4-isomer 2a and/or trans 1,2-isomer 3a were produced exclusively with these reagents and that the stoichiometry of BuMgX/CuX and the choice of solvent were critical to attain high regioselectivity and efficient yield. Reaction with Bu(2)Cu(CN)(MgCl)(2) and BuMgCl/CuX (X = CN, I; 10 mol %) both in THF produced 2a with 93-94% regioselectivity in 87-92% yields. On the other hand, BuCu(CN)(MgX) in THF, Bu(2)Cu(CN)(MgX)(2) in Et(2)O, and BuMgX/CuCN (10 mol %) in Et(2)O furnished 3a in good yields with >90% selectively, irrespective of X of BuMgX. In the nickel-catalyzed butylation of 1 with BuMgCl, NiCl(2)(dppp) among NiCl(2)(tpp)(2), NiCl(2)(dppf), and NiCl(2)(dppp) furnished the best result to produce 2a. The CuCN-based protocol was then applied to other alkyl Grignard reagents, which include Me, Et, (CH(2))(3)Ph, c-C(6)H(11), (CH(2))(6)OMOM, (CH(2))(9)CH=CH(2), and CH(2)Ph as the alkyl group (R(T)). In addition, the Mitsunobu inversion of 2a and 3a afforded the corresponding cis isomers stereoselectively with AcOH as an acid at -78 degrees C in toluene for 2a and with 4-(NO(2))C(6)H(4)COOH in THF at r.t. for 3a. No racemization during the alkylation was confirmed by the reaction using (1R,3S)-1 (>99% ee) to produce (1S,4S)-2a and (1S,2S)-3a, respectively.

The synthesis and chemoselective reactivity of 3-aminocyclopentadienones

Iron and cobalt complexes of 3-aminocyclopentadienones have been synthesized from the [2 + 2 + 1] cycloadditions of nitrogen acetylenes and pendant alkynes. Following decomplexation, the resulting 3-aminocyclopentadienones have been subjected to chemo- and regioselective cycloadditions with dienophiles and heterodienes.

Dicobalt octacarbonyl-catalyzed tandem cycloaddition reaction between diyne and diene under CO

Treatment of 1,7-diphenyl-1,6-heptadiyne and a symmetric butadiene such as 2,3-dimethyl-1,3-butadiene and 1,3-cyclohexadiene with Co(2)(CO)(8) (5 mol%) in CH(2)Cl(2) at 110 degrees C under 30 atm CO for 18 h afforded a 5.5.6 tricyclic enone in high yields. For unsymmetrical dienes such as 2-methyl-1,3-butadiene, 2-methyl-1, 3-pentadiene, and 3-methyl-1,3-pentadiene, two separable regioisomers were obtained. The catalytic reactions described are experimentally quite simple and provide a very useful synthetic procedure for the syntheses of [5.5.6] tricyclic enones.

Design, Synthesis, and Application of Chiral Nonracemic Lithium Amide Bases in Enantioselective Deprotonation of Epoxides

The reaction of epoxides with chiral nonracemic lithium amide bases, designed and prepared from (R)-phenylglycine, has been studied in detail. A maximum of 80% ee was obtained for conversion of cyclohexene oxide to (S)-2-cyclohexen-1-ol. Enantioselective deprotonation of a variety of other epoxides was studied. A cyclopentanoid core unit for prostaglandin synthesis was synthesized in 97% ee.