Chiral bicyclic guanidine-catalyzed enantioselective reactions of anthrones

Chiral bicyclic guanidine 1 was found to be an excellent catalyst for reactions between anthrones and various dienophiles. The catalyst can tolerate a range of substituents and substitution patterns, making several anthrone derivatives suitable for this reaction. Both Diels-Alder and Michael adducts were obtained in excellent yields, high regioselectivities, and high enantioselectivities. This is the first case of a highly enantioselective base-catalyzed anthrone Diels-Alder reaction.     

CoTPP-catalyzed reaction of saturated bicyclic endoperoxides

Saturated bicyclic endoperoxides were exposed to CoTPP (Cobalt-meso-tetraphenylporphyrine) in chloroform, the peroxide bond was cleaved and a mixture of products arising from fragmentation and reduction obtained.     

A novel bicyclic ketal fragmentation reaction

Bicyclic ketals of the 6,8-dioxabicyclo[3.2.1]octane series are specifically cleaved to give δ, ε-unsaturated ketones by treatment of the ketal with acetyl iodide.     

Chiral bicyclic guanidines: a concise and efficient aziridine-based synthesis

A series of chiral bicyclic guanidines, either symmetrical or non-symmetrical, was synthesized using a concise and efficient aziridine-based synthetic methodology. Starting from commercial amino alcohols, five synthetic steps were performed, with only three requiring chromatographic purification, giving the desired guanidines in 43-71% overall yield. Preliminary studies using these guanidines showed moderate enantioselectivity for several Michael reactions.     

Chiral bicyclic phosphoramidites--a new class of ligands for asymmetric catalysis

The development of new ligands for catalytic asymmetric C-C bond formation is of great interest to organic synthesis. We describe here a new class of chiral phosphoramidites that embody one or two binaphthol units attached to an achiral azabicyclic [3.3.1] or [3.3.0] framework. These ligands were easily accessible from (R)1,1'-binaphthyl-2,2'-dioxaphosphorchloridite (4) and the corresponding heterobicyclic core 1, 2, or 3. They were employed in enantioselective Cu-catalyzed additions of different dialkylzinc reagents to cyclic and acyclic enones. The chiral ketones were obtained with an enantiomeric ratio up to 91:9. The choice of the best ligand proved to be strongly dependent on each substrate. In addition, ligand 6 was found to be the most suitable for Rh-catalyzed hydrogenations of a,beta-unsaturated esters, giving rise to dimethyl 2-methylsuccinate and methyl N-acetylalaninate with enantiomer ratios up to 95:5.     

Phosphoneaminoethylation of spirophosphoranes

Conclusions The N--dialkylphosphonaminoethylation of 1,4,6,9-tetraoxa-5-phosphaspiro-(4,4)-nonane was accomplished.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1644–1646, July, 1970.     

Chiral aminocyclopentene-based cycloaddition strategies to bicyclic [3.3.0] rings

Two cycloaddition methods were applied to chiral protected aminocyclopentenes 2 and 9 and provided novel bicyclic products 3 and 4 in good yields. The explanation for the observed stereochemistry was based on the sterically encumbered β-face forcing the cycloadditions to occur on the α-face of the cyclopentene ring. The stereochemistry of 4 was confirmed by X-ray of the fumarate salt 10 and showed the trans-relationship between the newly formed ring and the chiral –NHBoc group.     

Intramolecular ene reaction of a chiral bicyclic lactam

The preparation of bicylic lactam 2 is described, employing an acetoacetate-based synthesis of 1,4-ketoacid 3. The lactam 2 was shown to undergo a thermal ene reaction at 280-300 degrees C to afford tricycle 7. Reduction of the ene product followed by removal of the chiral auxiliary fragment provided the unusual lactam system 9 in highly enantioenriched form.     

Cascade reaction synthesis of multisubstituted bicyclic pyridone derivatives

An efficient synthesis of novel bicyclic pyridone derivatives via cascade reaction of heterocyclic ketene aminals (HKAs) and 4-arylmethylene-2-phenyloxazol-5(4H)-ones in the presence of acetic acid has been established. Significantly, the protocol affords a straightforward approach to the construction of multisubstituted bicyclic pyridones in which one C–O bond was cleaved and new C–C and C–N bonds were formed in one pot under mild conditions.     

Chiral bicyclic imidazolium salts as a new class of N-heterocyclic carbene precursors

A N(1)-C(5) bridged chiral bicyclic imidazole with a morpholine framework was synthesized from an enantiopure 2-amino alcohol. The resultant imidazole reacted with various electrophiles, including primary and secondary alkyl halides, benzyne, and an electron-deficient aryl halide, to give the corresponding imidazolium salts. Some of the imidazolium salts were found to have potential as the precursor of a chiral N-heterocyclic carbene catalyst; by the direct annulation of an enal and a ketone through the intermediacy of a homoenolate and an activated carboxylate, the target lactone was obtained in an enantiomerically enriched form (up to 66% ee).     

Addition of spirophosphoranes to unsaturated compounds

Conclusions The addition of some spirophosphoranes to the carbon-carbon double bond was accomplished.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2803–2804, December, 1970.     

Chiral tetraaminophosphonium carboxylate-catalyzed direct Mannich-type reaction

The cooperative asymmetric catalysis of chiral tetraaminophosphonium carboxylate (P,S)-1.OCOR has been established, and its synthetic utility has been successfully demonstrated by application to the highly enantioselective direct Mannich-type reaction of azlactones with N-sulfonyl imines. The present study stimulates the cultivation of the potential of the chiral quaternary onium salt catalysis by the structural modification of organic anion.     

Sequential catalytic role of bifunctional bicyclic guanidine in asymmetric phospha-Michael reaction

The catalytic mechanism and origin of enantioselectivity of bicyclic guanidine-catalyzed phospha-Michael reaction between diphenyl phosphine oxide and β-nitrostyrene were investigated by DFT calculations at M06-2X/cc-pVTZ//M06-2X/cc-pVDZ level in conjunction with the implicit SMD solvation method. The catalyst is found to be involved in all 3 steps of the proposed catalytic cycle, namely (1) tautomerization of phosphine oxide, (2) C-P bond formation and (3) concerted hydrogen transfer. The bifunctional role of the guanidine catalyst is clearly demonstrated in all 3 key steps. Due to the geometry of the bicyclic guanidine catalyst, the preferred orientation of the reactants in the transition state of enantioselective C-P bond forming step favours the R enantiomer, in excellent accord with the observed enantioselectivity. Analysis of various transition states suggests that the asymmetric C-P bond formation is controlled by the hydrogen bonding interaction and steric effect between the catalyst and substrate. Various weaker C-H···X (X = N, O and π) interactions also play a role in stabilizing the key transition states.     

不对称diels-Alder反应中的手性催化剂

本文综述了近年来不对称Diels-Alder反应中手性催化剂研究的进展,对各类手性催化剂的性能和特点作了简要介绍.     

Synthesis of bicyclic 2,6-diketopiperazines via a three-step sequence involving an Ugi five-center,four-component reaction

A three-step sequence involving an Ugi five-center, four-component reaction (U-5C-4CR), amide N-detertbutylation and cyclocondensation has been developed for easy access to diverse bicyclic 2,6-diketopiperazine (2,6-DKP) derivatives. In the key step, aromatic aldehydes were successfully coupled with cyclic α-amino acids and isocyanides in the course of U-5C-4CR. Boron trifluoride-acetic acid complex was developed as a new N-detertbutylating agent effective at rt.     

Three-component domino reaction synthesis of highly functionalized bicyclic pyrrole derivatives

An efficient one-pot synthesis of highly functionalized bicyclic pyrrole derivatives by a three-component domino reaction of heterocyclic ketene aminals (HKAs), arylglyoxal monohydrate, and indoles in ethanol medium catalyzed by acetic acid is described. In this procedure, three sigma bonds were formed simultaneously. The present synthesis features excellent regio-selectivity, easy purification as well as simple starting materials.     

High-yield formation of giant bis(bicyclic) and crypt-tris(bicyclic) molecules under normal reaction conditions

We report the unexpected result of the reaction of 1, 3-bis[(9-anthrylmethoxy)methyl]benzene (1a) or 1,3, 5-tris[(9-anthrylmethoxy)methyl]benzene (1b) with tris(2-maleimidoethyl)amine (2) in homogeneous solution leading to giant bis(bicyclic) and crypt-tris(bicyclic) molecules. The anticipated, intractable solids are obtained in a condensed state reaction using an oscillating mill.     

A novel approach to the synthesis of bicyclic lactones via an interrupted Nazarov reaction of gem-divinyl dihydrofurans

[reaction: see text] A facile Lewis acid induced interrupted Nazarov reaction of gem-divinyl dihydrofurans to bicyclic lactones is described.