Allylboration Of Aldehydes Research Articles

Allylboration of Aldehydes

Allylboration of Aldehydes

ChemInform Abstract: Chiral Synthesis via Organoboranes. Part 32. Synthesis of B-(Cycloalk- 2-enyl)diisopinocampheylboranes of High Enantiomeric Purity via the Asymmetric Hydroboration of Cycloalka-1,3-dienes. Successful Asymmetric Allylborations of Aldeh

The hydroboration of cycloalka-1,3-dienes (CnH2n–4, n= 6, 7 and 8) with diisopinocampheylborane, (dIpc2BH or IIpc2BH) at –25°C provides highly enantiomerically pure B-(cycloalk-2-enyl)diisopinocampheylboranes, I or dIpc2BCnH2n–3( 93% ee). Surprisingly, these allylic borane derivatives retain their stereochemical integrity at –25 °C although such compounds are capable of undergoing racemization through rapid allylic rearrangements. Furthermore, the B-(cycloalk-2-enyl)diisopino-campheylboranes achieve allylborations of aldehydes at –78 °C and afford 1 -(cycloalk-2-enyl)alkan-1- ols in 90–95% ee and 100%syn-diastereoselectivity.

Chiral Brønsted acid-catalyzed allylboration of aldehydes.

The catalytic enantioselective allylation of aldehydes is a long-standing problem of considerable interest to the chemical community. We disclose a new high-yielding and highly enantioselective chiral Brønsted acid-catalyzed allylboration of aldehydes. The reaction is shown to be highly general, with a broad substrate scope that covers aryl, heteroaryl, alpha,beta-unsaturated, and aliphatic aldehydes. The reaction conditions are also shown to be effective for the catalytic enantioselective crotylation of aldehydes. We believe that the high reactivity of the allylboronate is due to protonation of the boronate oxygen by the chiral phosphoric acid catalyst.

ChemInform Abstract: Stereoselective Synthesis of Homoallylic Alcohols of the [2.2]Paracyclophane Series and Their Use as Auxiliaries in Asymmetric Allylboration of Aldehydes.

Stereoselectivity of allylboration of 4-formyl[2.2]paracyclophane, 4-acetyl[2.2]paracyclophane, and 4-hydroxy-5-formyl[2.2]paracyclophane was studied and the relative configurations of the homoallylic alcohols obtained were established. Optically pure (Sp,Sc)-(+)-4-(4-hydroxy-1-methylbut-3-enyl)[2.2]paracyclophane and (Rc,Sc)-(+)-4-hydroxy-5-(4-hydroxybut-3-enyl)[2.2]paracyclophane were synthesized. The possibility of using (Sp,Sc)-(+)-4-(4-hydroxy-4-methylbut-3-enyl)[2.2]paracyclophane as a recoverable chiral auxiliary in asymmetric allylboration of aldehydes was demonstrated.

Enantioselective synthesis of (E)-delta-stannyl homoallylic alcohols via aldehyde allylboration using alpha-stannylallylboranes generated by allene hydroboration followed by a highly diastereoselective 1,3-boratropic shift.

A highly enantioselective synthesis of (E)-delta-stannyl homoallylic alcohols 4 via aldehyde allylboration reactions of the double-chiral allylborane reagent 2a is reported. Allylborane 2a was generated from the hydroboration of commercially available allenylstannane 1 with ((d)Ipc)(2)BH at -40 to -20 degrees C followed by a kinetically controlled and highly diastereoselective 1,3-boratropic shift in intermediate 3a.

Stereoselective Synthesis of 2-Methyl-3-butene-1,2-diols

A new stereoselective synthesis of both syn and anti isomers of 2-methyl-3-butene-1,2-diols was developed. 1-Methylallenylborate hydroboration at room temperature generates kinetic intermediate (Z)-allylborane. It isomerizes to the thermodynamically more stable (E)-isomer at 85 ˚C. The following aldehyde allylboration generates target diols in good yields and stereoselectivities.

ChemInform Abstract: Rationally Improved Chiral Broensted Acid for Catalytic Enantioselective Allylboration of Aldehydes with an Expanded Reagent Scope.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Diversity‐Oriented Synthesis and Preliminary Biological Screening of Highly Substituted Five‐Membered Lactones and Lactams Originating from an Allylboration of Aldehydes and Imines.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Rationally Improved Chiral Brønsted Acid for Catalytic Enantioselective Allylboration of Aldehydes with an Expanded Reagent Scope

One of the most useful reactions in organic synthesis, the stereocontrolled addition of allylic metal reagents to carbonyl compounds, provides access to enantiomerically enriched homoallylic alcohols related to the acetate, propionate, and other oxygen-containing functionalities present in a large number of biologically active natural products and pharmaceutical drugs. In the search for an ideal carbonyl allylation methodology, the catalytic enantioselective allylboration presents numerous advantages such as a high chemo-, diastereo-, and enantiocontrol with stable and nontoxic pinacol allylic boronates. This article reports a rationally improved diol x SnCl(4) complex as chiral protic acid catalyst, which provides unprecedented levels of enantioselectivity in the catalytic allylation, methallylation, crotylation, and 2-bromoallylation of aliphatic aldehydes. The new diol, p-F-Vivol (4b), enables a more active diol x SnCl(4) catalyst that can compete more effectively with the background uncatalyzed allylboration. The usefulness of this optimized catalytic allylboration methodology was demonstrated with an efficient synthesis of the naturally occurring pyranone (+)-dodoneine and to the preparation of biologically important exomethylene-gamma-lactones.

SN2′ Boron‐Mediated Mitsunobu Reactions – A New One‐Pot Three‐Component Synthesis of Substituted Enamides and Enol Benzoates

AbstractThe conversion of (3‐hydroxy‐1‐propen‐1‐yl)boronates to substituted enamides and enol benzoates is readily achieved in a one‐pot procedure consisting of a regiocontrolled Mitsunobu reaction with convenient nucleophiles, followed by allylboration of aldehydes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Enantioselective silicon–boron additions to cyclic 1,3-dienes catalyzed by the platinum group metal complexes

Silaborations of 1,3-cyclohexadiene and 1,3-cycloheptadiene were achieved using catalysts prepared from different combinations of phosphorus ligands and group 10 metal compounds. For the six-membered compound, 1,4-adducts with up to 82% ee were obtained employing Pt(0) and phosphoramidite ligands. For the seven-membered diene optimal conditions were found using catalysts based on Ni(0), but the highest selectivity observed was merely 22% ee. No improvement of the chiral induction was obtained using chiral silylboranes in combination with chiral phosphoramidite ligands in the additions to 1,3-cyclohexadiene. The adduct obtained from cyclohexadiene was used in allylborations of aldehydes under microwave irradiation to produce homoallylic alcohols with moderate to good diastereoselectivity.

Catalytic Enantioselective Allyl- and Crotylboration of Aldehydes Using Chiral Diol•SnCl4 Complexes. Optimization, Substrate Scope and Mechanistic Investigations

We report a novel class of C2-symmetric chiral diols derived from the hydrobenzoin skeleton. The combination of these diols with SnCl4 under Yamamoto's concept of Lewis acid assisted Brønsted acidity (LBA catalysis) leads to high levels of asymmetric induction in the allylboration of aldehydes by commercially available allylboronic acid pinacol ester 1a. The corresponding homoallylic alcohol products of synthetically useful aliphatic aldehydes are obtained in excellent yields with up to 98:2 er. This combined acid manifold is also efficient in catalyzing the diastereo- and enantioselective crotylboration of aldehydes, thus providing the propionate units in >95:5 dr and up to 98:2 er. The X-ray crystal structure of the optimal diol x SnCl4 complex, Vivol (4m) x SnCl4, unambiguously shows the Brønsted acidic character of this LBA catalyst and its highly dissymmetrical environment. Further controls have ruled out a possible boron trans-esterification mechanism with the chiral diol and point to LBA catalyst-derived activation of the pinacol allylic boronates 1. Due to slow dissociation of the diol x SnCl4 complex, a small excess of diol is required in order to suppress a competing racemic cycle catalyzed by free SnCl4.

ChemInform Abstract: Preparation of a C2‐Symmetric Binol‐Derived Diol and Its Application in the Catalytic Enantioselective and Catalyst‐Controlled Diastereoselective Allylboration of Aldehydes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Preparation of a C2-Symmetric Binol-Derived Diol and Its Application in the Catalytic Enantioselective and Catalyst-Controlled Diastereoselective Allylboration of Aldehydes

A novel C 2-symmetric Binol-derived diol is described. It is readily applicable towards combined acid catalysis for the asym­metric allylboration of aldehydes to provide homoallylic alcohols in high enantioselectivities, and dictates the diastereoselectivity in the reaction of an achiral allylboronate with chiral aldehydes.

Practical and Efficient Multigram Preparation of a Camphor-Derived Diol for the Enantioselective Lewis Acid Catalyzed Allylboration of Aldehydes

[reaction: see text] Chiral diols are important molecules with widespread use as chiral auxiliaries and ligands in enantioselective synthesis. Therefore, efficient and practical syntheses of highly dissymmetrical nonracemic diols are still a meaningful pursuit. Two new routes to access camphor-derived chiral diol 1 have been developed. One route employs camphorquinone (3) as the starting material, affording in only two steps the desired diol in 55% overall yield. The second route, from camphor (2), leads to the desired diol in an efficient four-step synthesis, with an overall yield of 55%.

Scandium‐Catalyzed Allylboration of Aldehydes as a Practical Method for Highly Diastereo‐ and Enantioselective Construction of Homoallylic Alcohols.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Scandium-catalyzed allylboration of aldehydes as a practical method for highly diastereo- and enantioselective construction of homoallylic alcohols.

A general approach for the allylation of aldehydes using stable, air-tolerant camphor-based chiral allylboronates under Sc(OTf)3 catalysis is described. This practical methodology provides both syn and anti propionate units and other homoallylic alcohols with very high levels of diastereo- and enantioselectivity for several substrates, including functionalized aliphatic aldehydes useful toward the elaboration of complex natural products.

Acceleration Effect of Lewis Acid in Allylboration of Aldehydes: Catalytic Regiospecific, Diastereospecific, and Enantioselective Synthesis of Homoallyl Alcohols.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Enantioselective Reduction of Heteroaromatic β,γ‐Unsaturated Ketones as an Alternative to Allylboration of Aldehydes. Application: Asymmetric Synthesis of SIB‐1508Y.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Computer-aided design of chiral ligands. Part III. A novel ligand for asymmetric allylation designed using computational techniques.

[reaction: see text] Computer-aided design protocols to identify new chiral ligands for reactions proceeding through well-defined transition states are outlined. Ligand families are discovered via computational screening of large structural databases such as the Cambridge Structural Database. Using this method, a novel cis-decalin ligand has been identified as a chiral auxiliary for the allylboration of aldehydes. Synthesis, resolution, and evaluation revealed that this new auxiliary provided the aldehyde facial approach upon which the design was predicated.