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The first synthesis of a recently isolated antiproliferative diarylindolizidine alkaloid, (+)-fistulopsine B, was achieved. The synthesis features the use of an organocatalytic ketone-nitrostyrene Michael addition as the key step.

A modular synthesis of aspulvinones A, B, C, D, E, G and the recently isolated aspulvinone Q was developed. The methodology features a highly stereoselective aldol condensation of diazotetronic acid with aldehydes to provide 5-arylidene diazotetronates. Subsequent catalytic intermolecular C-H insertion reactions of the arylidene tetronates with arenes provide a series of naturally occurring aspulvinones including aspulvinones C, D and Q which have not been synthesized before. Variation of the aldehyde and the arene components furnishes synthetic analogues of the aspulvinones.

Concise syntheses of the polyketide natural product (–)-muricatacin and (–)-(R,R)-L-factor (natural product enantiomer) were achieved in four steps by employing an organocatalytic asymmetric direct vinylogous aldol reaction of γ-crotonolactone and suitable aliphatic aldehydes as the key step.

An enantioselective, biomimetic organocatalytic synthesis of 4-arylquinolizidin-2-ones, key intermediates in the synthesis of several Lythraceae alkaloids, was developed. The methodology features S...

A variety of 3-aryl tetronic acids have been synthesized by an undirected, intermolecular C-H functionalization of arenes with 3-diazofuran-2,4-dione. This methodology featured as a key step in the synthesis of a series of naturally occurring 3-aryl-5-arylidene tetronic acids (pulvinates) from commercially available tetronic acid. Salient features of the pulvinic acid synthesis include a one-step, stereoselective synthesis of the C5 arylidene group and a single step introduction of the C3 aryl substituent.

A modular, stereoselective synthesis of E-3-(arylidene)-5-(alkyl/aryl)-2(3H)-furanones was developed. The methodology features regioselective addition of β-aryl acrylic acids to iodoacetylenes to furnish the Z-acyloxy iodoalkenes. A stereoselective 5-exo-trig Mizoroki–Heck reaction of the acyloxy iodoalkenes generates the target E-2(3H)-furanones. The approach was applied in a formal synthesis of the naturally occurring kinase inhibitor BE-23372M.

A concise synthesis of 2-t-butoxycarbonyl allyl vinyl ethers by regioselective Petasis methylenation and stereoselective Suzuki–Miyaura cross-coupling reactions of iodoallyl t-butyl oxalates was developed. Ethers with a terminally unsubstituted vinyl group and a terminally disubstituted allyl portion are readily accessible by this method. The enantioselective Claisen rearrangement of representative allyl vinyl ethers was examined.

The first examples of an organocatalytic Michael addition of a ketone to in situ generated α-nitrostyrenes are reported. A suitably functionalized γ-nitroketone obtained from the organocatalyzed Michael addition was converted into (+)-2-epi-lasubine II, the immediate synthetic precursor of (+)-lasubine II and (-)-subcosine II (enantiomers of the natural quinolizidine alkaloids). Two of the three stereocenters in (+)-2-epi-lasubine II are set by the Michael reaction.

An enantioselective synthesis of functionalized quaternary stereocenters was developed from amino alcohol derived (bromoalkylidene)morpholinones. Stereoselective cross-coupling of the morpholinones with arylboronic acids or alkyl trifluoroborates provided a variety of disubstituted alkylidenemorpholinones. A highly stereoselective Prins reaction of the cross-coupling products generated the target quaternary stereocenter. The Prins products are readily converted into a variety of acyclic, enantiomerically enriched, functionalized building blocks with a quaternary stereocenter.

The enantioselective organocatalytic direct vinylogous aldol reaction of γ-crotonolactone and a suitable aldehyde was utilized in the synthesis of a functionalized γ-butenolide. The γ-butenolide (aldol product) was stereoselectively converted into a 5-aminoalkyl butyrolactone, which isomerized to the key 2,3-disubstituted piperidinone, a common intermediate to (+)-febrifugine and (+)-halofuginone.

An efficient route to functionalized indolizidines from an enantiomerically enriched γ-nitro ketone is described. The nitro ketone is obtained by an organocatalytic, enantioselective ketone-nitro alkene Michael addition. Oxidative ring expansion of the nitro ketone and subsequent methanolysis provides a 8-nitro-4-oxooctanoate. This is stereoselectively transformed to the key, functionalized indolizidine intermediate which is readily converted to (+)-ipalbidine and (+)-antofine.

Secondary–secondary diamines derived from S-proline are efficient catalysts for the ketone–nitroalkene Michael addition reaction. The stereoselectivity of the Michael addition is dependant on the pKa of the N-substituted aminomethyl pendant in these diamines. N′-Aryl aminomethyl pyrrolidines provide γ-nitroketones with moderate to good enantiomeric excess (65–92%). Removal of the hydrogen-bond donor group by N-methylation results in a dramatic reduction of enantioselectivity (average ee 6%).

Guanidinyl pyrrolidines derived from 'S'-proline are effective catalysts for the enantioselective conjugate addition of malonate, nitroalkane and other carbon and heteroatom nucleophiles to cyclohexenone and cyclopentenone in the absence of basic additives. The stereoselectivity is strongly dependent on catalyst loading as well as reaction concentration.

An enantioselective synthesis of functionalized quaternary stereocenters was developed from amino alcohol derived (bromoalkylidene)morpholinones. Stereoselective cross-coupling of the morpholinones with arylboronic acids or alkyl trifluoroborates provided a variety of disubstituted alkylidenemorpholinones. A highly stereoselective Prins reaction of the cross-coupling products generated the target quaternary stereocenter. The Prins products are readily converted into a variety of acyclic, enantiomerically enriched, functionalized building blocks with a quaternary stereocenter.

An efficient enantioselective synthesis of β,β-dialkyl α-hydroxy γ-butyrolactones, analogues of pantolactone, has been developed employing a stereoselective Prins reaction of chiral alkylidene morpholinones, as the key step. Enantioselective synthesis of a naturally occurring pantolactone homologue and a spiro analogue of pantolactone was achieved with this protocol.

The direct aldol reaction of γ-crotonolactone and various aromatic aldehydes is catalyzed by bifunctional aminothiourea and aminosquaramide organocatalysts to provide diastereomerically and enantiomerically enriched 5-substituted 2(5H) furanones (γ-butenolides). The reaction is a simple alternative to the classical vinylogous aldol reaction of silyloxy furans.

Trityl isothiocyanate resin [1], prepared from commercially available trityl chloride resin, is a useful precursor of the trityl thiosemicarbazide resin [2]. This resin can be employed in the solid-phase synthesis of a variety of supported isatin beta-thiosemicarbazones [4] and their Mannich derivatives [6]. A variety of thioureas [7] can be easily prepared by the reaction of [1] with amines. The supported thioureas are directly and efficiently converted to 2-aminothiazole-5-carboxylates [8] by reaction with methyl 2-chloroacetoacetate.

Magnesium bromide is an efficient catalyst for the acetylation and benzoylation of a variety of primary and secondary alcohols with the respective acid anhydrides at ambient temperature. Acetylation of tertiary alcohols requires subambient temperature to suppress competing dehydration. Coordinating solvents retard the acylation process.

A new enantioselective approach to α-alkyl-α-hydroxy-γ-butyrolactones employing (1R,2S)-ephedrine-derived chiral allyl morpholinones as starting materials is described.

Scandium triflate is an efficient catalyst for diazocarbonyl insertion reactions into OH, SH and carbamate NH bonds. The OH and SH insertion reactions proceed at ambient temperature and selective OH insertion is possible in the presence of a carbamate NH. A novel approach to α-amino acids involving intramolecular carbene NH insertion as the key step has been demonstrated.

Cyclopropanation of chiral α-alkoxy acrylamides derived from 1R,2S-ephedrine and α-keto acids provides cyclopropyl morpholinones with good diastereoselectivity. Removal of the ephedrine portion generates α-hydroxycyclopropane carboxamides which are readily converted to enantiomerically enriched α-hydroxycyclopropanecarboxylic acids.

An expedient enantioselective approach to (R)-homocitric acid lactone from an ephedrine-derived morpholine-dione, a cationic glycolate equivalent, is described.

N-Acylation of prolinol with α-ketoacid chlorides results in concomitant hemiacetalization of the α-keto amide by the prolinol hydroxyl group. (R) or (S) α-hydroxy acids are obtained with good enantiomeric excess by stereodivergent reduction of these hemiacetals. Reaction with Grignard reagents at ambient temperature furnishes (R) α-alkyl mandelic acids with good stereoselectivity.

Intramolecular reductive cross-coupling of unsymmetrical dibenzylidene sulfamides generates the corresponding cyclic sulfamides in good yield. These intermediates are readily converted to the free, unsymmetrical 1,2-diaryl ethanediamines.

An efficient synthesis of functionalized quinolizidines was developed from an enantiomerically enriched γ-nitroketone, which is easily prepared by an organocatalytic ketone–nitroalkene Michael addition. Oxidative ring expansion of the nitroketone followed by reductive ring-opening leads to a suitably functionalized nitrodiol which is an intermediate to the title compounds.

The γ-butenolide obtained from an organocatalyzed, direct vinylogous aldol reaction of γ-crotonolactone and benzaldehyde serves as the key starting material in the expedient synthesis of a 3-hydroxy-2-phenyl piperidine intermediate which is converted to the target 2,3-disubstituted piperidines.

The reaction is catalyzed by bifunctional organocatalysts (I) and provides diastereomerically and enantiomerically enriched 5-substituted 2(5H)-furanones (IV).

An ephedrine-derived morpholine dione is employed in the synthesis of chiral alkylidene morpholinones that are efficiently converted to β-substituted α,γ-dihydroxy butyramides, precursors of the corresponding butyrolactones. Enantioselective synthesis of a spiro analog of pantolactone as well as a naturally occurring pantolactone homolog is achieved with this protocol.

The asymmetric electrophilic amination of phosphorus-stabilized anions derived from chiral oxazaphosphorinanes and diazaphospholidines is described. Trisyl azide is the reagent of choice for the amination process. The reaction is shown to be dependent on auxiliary structure, nature of the P-alkyl substituent and choice of amination procedure. Using the oxazaphosphorinanes 1a and cis-1e a high level of asymmetric induction can be achieved. Scalemic cis-1e provides the α-aminophosphonic acid 13 with 92% e.e. in the (S) antipode. The implications for conformation and effect of auxiliary structure on stereoselectivity are discussed.

Treatment of methyl N-methylthionocarbamate (2a) with a catalytic amount of iodine or conc. H2SO4 results in the unexpected formation of the isomer, methyl N-methylthiolcarbamate (3a) in 90% yield. This has subsequently been transformed into methyl N-methylcarbamate (4a), by sodium methoxide. A curious transformation of methyl N-methyldithiocarbamate (1a) to (4a) on prolonged treatment with sodium methoxide is also discussed.

N-Acylation of prolinol with α-ketoacid chlorides results in concomitant hemiacetalization of the α-keto amide by the prolinol hydroxyl group. (R) or (S) α-hydroxy acids are obtained with good enantiomeric excess by stereodivergent reduction of these hemiacetals. Reaction with Grignard reagents at ambient temperature furnishes (R) α-alkyl mandelic acids with good stereoselectivity.

Cyclopropanation of chiral α-alkoxy acrylamides derived from 1R,2S-ephedrine and α-keto acids provides cyclopropyl morpholinones with good diastereoselectivity. Removal of the ephedrine portion generates α-hydroxycyclopropane carboxamides which are readily converted to enantiomerically enriched α-hydroxycyclopropanecarboxylic acids.

A new enantioselective approach to α-alkyl-α-hydroxy-γ-butyrolactones employing (1R,2S)-ephedrine-derived chiral allyl morpholinones as starting materials is described.

The Prins reaction of a chiral alkylidene morpholinone derived from (1R,2S)-ephedrine and 3-methyl-2-oxobutanoic acid proceeds with good diastereoselectivity to generate a spiro bis-acetal. Lewis a...

An ephedrine-derived morpholine dione is employed in the synthesis of chiral alkylidene morpholinones that are efficiently converted to β-substituted α,γ-dihydroxy butyramides, precursors of the corresponding butyrolactones. Enantioselective synthesis of a spiro analog of pantolactone as well as a naturally occurring pantolactone homolog is achieved with this protocol.

The asymmetric electrophilic amination of phosphorus-stabilized anions derived from chiral oxazaphosphorinanes and diazaphospholidines is described. Trisyl azide is the reagent of choice for the amination process. The reaction is shown to be dependent on auxiliary structure, nature of the P-alkyl substituent and choice of amination procedure. Using the oxazaphosphorinanes 1a and cis-1e a high level of asymmetric induction can be achieved. Scalemic cis-1e provides the α-aminophosphonic acid 13 with 92% e.e. in the (S) antipode. The implications for conformation and effect of auxiliary structure on stereoselectivity are discussed.

Secondary–secondary diamines derived from S-proline are efficient catalysts for the ketone–nitroalkene Michael addition reaction. The stereoselectivity of the Michael addition is dependant on the pKa of the N-substituted aminomethyl pendant in these diamines. N′-Aryl aminomethyl pyrrolidines provide γ-nitroketones with moderate to good enantiomeric excess (65–92%). Removal of the hydrogen-bond donor group by N-methylation results in a dramatic reduction of enantioselectivity (average ee 6%).

[reaction: see text] The Prins reaction of a chiral alkylidene morpholinone derived from (1R,2S)-ephedrine and 3-methyl-2-oxobutanoic acid proceeds with good diastereoselectivity to generate a spiro bis-acetal. Lewis acid mediated diastereoselective reductive cleavage of the spiro acetal and subsequent removal of the ephedrine portion generates a alpha-hydroxy-gamma-methoxy carboxamide which is readily converted to (S)-(+)-pantolactone with high enantiomeric excess.

Enantioselective routes to functionalized, seven-, eight-, and nine-membered oxacycles that are amenable to further elaboration have been developed. Salient features of the methodology include highly diastereoselective and regioselective transformations of an ephedrine-derived epoxy morpholinone to functionalized precursors of the oxacycles. The ephedrine scaffold exerts remote stereocontrol in the functionalization of the appended oxacycle. [reaction: see text]

Simple, chiral, pyrrolidine-based diamine and triamine derivatives that incorporate the secondary−secondary diamine motif are efficient catalysts for the highly diastereoselective and enantioselective Michael addition of cyclic ketones to 2-nitrovinyl arenes. The highest selectivities are obtained when these catalysts are used in conjunction with protonic acids. Steric factors in the substrate and the size of the acid additive play an important role in stereoselection.

[reaction: see text] An expedient, enantioselective synthesis of a key precursor to (-)-quinic acid has been achieved from an ephedrine-derived morpholine-dione. The salient features of this approach are a highly diastereoselective conversion of the dione to a dialkenyl morpholinone and a subsequent ring-closing metathesis reaction. Removal of the ephedrine portion generates an enantiomerically enriched hydroxycyclohexene carboxamide that is readily converted to the quinic acid precursor.