Mauro Pineschi

Lanthanide(III) trifluoromethanesulfonates as extraordinarily effective new catalysts for the aminolysis of 1,2-epoxides

Abstract Lanthanide(III) trifluoromethanesulfonates (triflates), such as Yb(OTf) 3 , Nd(OTf) 3 and Gd(OTf) 3 , catalyze in a extraordinarily efficient way the aminolysis of 1,2-epoxides, affording the corresponding β-amino alcohols, at room temperature and in a non-protic solvent (CH 2 Cl 2 or toluene), in very good yields. The reactions are completely anti stereoselective and highly regioselective.

Recent Progress in the Synthesis of 2,3-Dihydrobenzofurans

Introduction ..........................................................................................386 I. Natural Occurrence of 2,3-Dihydrobenzofurans................................387 II. Synthesis by Dehydrative Methods .....................................................389 III. Radical Cyclizations and Electrocyclizations .....................................391 IV. Biomimetic Couplings and Cycloadditions .........................................393 V. Biomimetic Asymmetric Synthesis ......................................................397 VI. Synthesis via Benzyne ...........................................................................399 VII. Intramolecular Substitutions of ortho-Allylphenols without Metal Catalysts .........................................................................................401 VIII. Transition Metal-Catalyzed Processes ................................................402 1. Transition Metal-catalyzed Nucleophilic Substitutions............................402 2. Transition Metal-catalyzed Intramolecular Hydroalkoxylations ..............405 3. Transition Metal-catalyzed Insertion-Cyclizations ..................................407 4. Palladium-catalyzed Intramolecular Heck-type Cyclizations ...................409 IX. Anionic Cyclizations .............................................................................412 X. Miscellaneous Methods ........................................................................413 References..............................................................................................415

Catalytic Enantioselective Carbon-Carbon Bond Formation by Addition of Dialkylzinc Reagents to Cyclic 1,3-Diene Monoepoxides.

Abstract Chiral copper complexes of 2,2′-binaphthyl-based phosphorus amidites are shown to be highly effective catalysts for the conjugate addition of dialkylzinc reagents to vinyloxiranes. The corresponding allylic alcohol reaction products (S N 2′-pathway) were obtained with moderate to high regioselectivity. Both direct- (S N 2-pathway) and conjugate-opening addition (S N 2′-pathway) seem to proceed with complete anti stereoselectivity. The enantioselectivity of these addition reactions according to a kinetic resolution protocol turned out to be high (>90% ee) with 1,3-cyclohexadiene and 1,3-cycloheptadiene monoepoxides.

Regiochemical control of the ring opening of 1,2-epoxides by means of chelating processes. 8. Synthesis and ring opening reactions of cis- and trans- oxides derived from 3-benzyloxycyclohexene and 2-benzyloxy-5,6-dihydro-2H-pyran

Abstract The regiochemical outcome of the ring opening of 1,2-epoxides bearing polar remote functionalization through chelation processes assisted by metal ions, was verified in cyclic oxirane systems having the polar functionality in an allylic position to the oxirane ring. The diastereoisomeric cis/trans epoxide pairs 5,6 and 7,8 derived from 3-benzyloxycyclohexene, and 2-benzyloxy-5,6-dihydro-2H-pyran, respectively, were prepared and several of their opening reactions were studied. The regioselectivity observed largely depends on the reaction conditions (standard or metal-assisted) and, interestingly, on the nature of the nucleophile used.

Regio- and Stereoselective Ring Opening of Enantiomerically Enriched 2-Aryl Oxetanes and 2-Aryl Azetidines with Aryl Borates

The regioselective ring opening of 2-aryl-substituted four-membered heterocyclic rings with phenols, including catechol, was achieved by the use of aryl borates in mild and neutral reaction conditions without the aid of any transition metal catalysts. While N-alkyl azetidines were found not to be reactive, optically active N-tosyl azetidines gave the corresponding beta-aryloxy amines in a racemic form, thus indicating the considerable carbocationic character of the transition state. The introduction of a hydroxyl group in the azetidine ring (i.e., an azetidinol), able to anchor the aryl borate and to direct the subsequent nucleophilic delivery, was shown to determine the ring-opening process with predominant inversion of configuration. When enantiomerically enriched 2-aryl oxetanes were used, the reduced extent of racemization observed (up to 93:7 er) was rationalized by an intramolecular delivery through a six-membered transition state, giving beta-aryloxy alcohols with a predominant retention of configuration (i.e., a syn-stereoselective ring opening). The aryloxy alcohols obtained, endowed with suitable functionalities, can be cyclized to give access to enantiomerically enriched 2-aryl-1,5-benzodioxepins.

Nickel-catalyzed borylative ring opening of vinyl epoxides and aziridines.

A mild ring opening of vinyl epoxides and aziridines with B(2)Pin(2) catalyzed by Ni(0)-Binap affords new functionalized allylic boron derivatives which undergo sequential transformations. The uncatalyzed allylation of aldehydes allows obtaining challenging bishomoallylic alicyclic 1,3-diols and 1,3-amino alcohols with remarkably high stereoselectivities. Valuable trans-bisallylic 1,4-amino alcohols can be obtained by a simple oxidation.

Regiochemical control of the ring opening of 1:2-epoxides by means of chelating processes. 10. Synthesis and ring opening reactions of mono- and difunctionalized cis and trans aliphatic oxirane systems

Abstract The regiochemical outcome of the ring opening of 1:2-epoxides through chelation processes assisted by metal ions, was verified in mono- and difunctionalized aliphatic oxirane systems bearing the heterofunctionality (OR) in an homoallylic and/or allylic relationship to the oxirane ring. The effect of the distance of the OR functionality from the oxirane ring and of the type of protective group on the regiochemical outcome of these systems is examined. In some cases, the use of LiClO4 or Mg(ClO4)2 as the promoting metal salt makes it possible the obtainment of a nice regioalternating process.

Copper-catalyzed enantioselective allylic alkylation ring-opening reactions of small-ring heterocycles with hard alkyl metals

Copper-catalyzed enantioselective allylic substitution reactions with organometallic reagents have aroused a great deal of interest in recent years. Small-ring heterocycles, such as epoxides and aziridines, have proven to be valuable leaving groups in copper-catalyzed asymmetric allylic alkylations with organometallic reagents. Some successful combinations of an organometallic reagent and an external chiral ligand for the enantioselective addition of dialkylzinc reagents to racemic and symmetrical allylic 1,2- and 1,4-epoxides are described. For this purpose, chiral copper complexes of phosphoramidite ligands, having an electron-deficient phosphorus atom, proved to be highly effective catalysts. Our experimental work has shed some light on the mechanism of a copper-catalyzed allylic alkylation and supports the notion that the reductive elimination step is the regio- and stereodetermining step.

Synthesis and Ring-Opening Reactions of the Diastereoisomericcis- andtrans-Epoxides Derived from 3-(Benzyloxy)cyclopentene and 2-(Benzyloxy)-2,5-dihydrofuran

The regiochemical outcome of the ring-opening of epoxides bearing remote polar functionalities has been established in the case of carbocyclic (1 and 2) and the corresponding furanosidic (3 and 4) title epoxides. Under standard conditions, the regioisomeric C-1 products are the sole (from trans epoxides 2 and 4) or predominant (from cis epoxides 1 and 3) ring-opening products. However, under chelating conditions, and only in the case of the cis epoxides 1 and 3, a consistent increase in C-2 selectivity is unexpectedly observed.

Yttrium triflate-catalyzed addition of lithium enolates to 1,2-epoxides. Efficient synthesis of γ-hydroxy ketones

A simple, efficient method is described for the synthesis of γ-hydroxy ketones by the direct opening of 1,2-epoxides with lithium enolates derived from simple ketones in anhydrous toluene, in the presence of Y(OTf)3.