Intramolecular Allylboration Research Articles

ChemInform Abstract: Stereocontrol in Allylboration Reactions

Abstraat: Crotyl-boronates add to aldehydes with high simple diastereoselection, such that E-crotyl-boronates give d-homoallyl alcohols, and Z-crotyl-boronates their =-counterparts. This reaction has been extended to stereoselective ring closure reactions by intramolecular allylboration. Moreover, by using suitably substituted crotyl boronates homoallyl alcohols having quarternary stereogenic carbon centers have been obtained with good diastereoselection. The development of chiral crotyl boronate reagents, having an additional stereogenic center a to the boron atom, allowed reactions with aldehydes to be accomplished with full transfer of chirality; i.e. control of the absolute configuration of the products.

Total Synthesis of Jimenezin via an Intramolecular Allylboration

[structure: see text] An efficient total synthesis of the annonaceous acetogenin jimenezin was achieved. The key steps used were a highly stereoselective intramolecular allylboration to establish the tetrahydropyran ring and an intramolecular Williamson reaction to close the tetrahydrofuran ring.

Platinum‐Catalyzed Tandem Diboration/Intramolecular Allylboration: Diastereoselective Access to Cyclohexanes Bearing 1,3‐Diols.

A tandem reaction sequence consisting of platinum-catalyzed diboration of 1,3-dienes followed by intramolecular allylboration and oxidative hydrolysis has been developed for constructing cyclic structures that bear a 1,3-diol. This methodology has proven effective for synthesizing cyclohexanes from dienals in good yields (44-64%) to generate diols containing two new vicinal stereocenters, one of which is quaternary. The products are obtained in high regio- and diastereomeric ratios (>19:1). A preexisting stereocenter on the substrate can provide high levels of asymmetric induction in the product.

Platinum-Catalyzed Tandem Diboration/Intramolecular Allylboration: Diastereoselective Access to Cyclohexanes Bearing 1,3-Diols

A tandem reaction sequence consisting of platinum-catalyzed diboration of 1,3-dienes followed by intramolecular allylboration and oxidative hydrolysis has been developed for constructing cyclic structures that bear a 1,3-diol. This methodology has proven effective for synthesizing cyclohexanes from dienals in good yields (44-64%) to generate diols containing two new vicinal stereocenters, one of which is quaternary. The products are obtained in high regio- and diastereomeric ratios (>19:1). A preexisting stereo­center on the substrate can provide high levels of asymmetric induction in the product.

Intramolecular Allylboration of γ‐(ω‐Formylalkoxy)allylboronates for Syntheses of trans‐ or cis‐2‐(Ethenyl)tetrahydropyran‐3‐ol and 2‐(Ethenyl)oxepan‐3‐ol.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Intramolecular allylboration of γ-(ω-formylalkoxy)allylboronates for syntheses of trans- or cis-2-(ethenyl)tetrahydropyran-3-ol and 2-(ethenyl)oxepan-3-ol

3-Alkoxy-1-alkynes 4 were hydroborated with pinacolborane (HBpin) to give 3-alkoxy-1-alkenylboronates 5 . The latter gave ( E)-3-alkoxyallylboronates ( 8 : ( E)-(MeO) 2CHCH 2(CH 2) n CH 2OCHCHCH 2Bpin, n=1–3) when they were subjected to iridium-catalyzed isomerization of the double bond. The corresponding ( Z)-isomers 10 were synthesized by nickel-catalyzed isomerization of 5 . Both allylboronates underwent intramolecular allylboration leading to the formation of trans-2-(ethenyl)tetrahydropyran-3-ol or 2-(ethenyl)oxepan-3-ol from 8 and the corresponding cis-isomers from 10 in the presence of Yb(OTf) 3 (20 mol%) in aqueous acetonitrile at 90°C.

ChemInform Abstract: Stereoselective Synthesis of Alcohols. Part 53. (E)‐γ‐Alkoxyallylboronates: Generation and Application in Intramolecular Allylboration Reactions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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.

Stereoselective synthesis of alcohols. Part LIII. (E)-γ-Alkoxyallylboronates: generation and application in intramolecular allylboration reactions

Alkoxyalkynes 9 may be hydroborated with pinacol borane, preferentially under Cp2ZrHCl catalysis, to give the vinylboronates 10. The latter, when subjected to the Matteson–Brown homologation with LiCH2Cl, give rise to the (E)-γ-alkoxyallylboronates 3 in good yield. This reaction sequence has been used to generate the (E)-γ-alkoxyallylboronates 14, 21, 26 and 31, which were the starting point for intramolecular allylboration reactions leading to the trans-disubstituted tetrahydropyrans 8 and 22, as well as hydrooxepans 27 and 32.

ChemInform Abstract: A Sequence of Palladium‐Catalyzed Borylation of Allyl Acetates with Bis(pinacolato)diboron and Intramolecular Allylboration for the Cyclization of Oxo‐2‐alkenyl Acetates.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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: Substituted Oxocanes by Intramolecular Allylboration Reactions. Entry to an Efficient Synthesis of (+)‐Laurencin.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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.

A Sequence of Palladium-Catalyzed Borylation of Allyl Acetates with Bis(pinacolato)diboron and Intramolecular Allylboration for the Cyclization of Oxo-2-alkenyl Acetates

Abstract The cross-coupling reaction of bis(pinacolato)diboron with oxo-2-alkenyl acetates in toluene at 50 °C in the presence of Pd(dba)2/2 AsPh3 (3 mol%) to give allylboronates was followed by the intramolecular allylboration at 100 °C. The sequence provided cyclic homoallyl alcohols in high yields.

Substituted Oxocanes by Intramolecular Allylboration Reactions. Entry to an Efficient Synthesis of (+)-Laurencin

Δ5-Oxocenes, such as cis-3-hydroxy-2-vinyl-Δ5-oxocenes, can be generated by an intramolecular aldehyde−allylboration reaction. This allowed a rapid and stereoselective access to the trisubstituted oxocene 24 which had been transformed by the Holmes group into (+)-laurencin. The key feature of this effective intramolecular allylboration reaction is that both the aldehyde and the allylboronate functionality have been generated in a masked form in situ. They are liberated by an aqueous workup which initiates the ring closure reaction.

Stereoselective Synthesis of Alcohols, L. Synthesis and Conformational Studies of 1,5‐Dioxa‐cis‐decalin

Abstractcis‐2‐Vinyltetrahydropyran‐3‐ol (6) is accessible by a selective intramolecular allylboration reaction. Compound 6 was converted into 1,4‐dioxa‐cis‐decaline (4) and cis‐syn‐cis‐perhydrotrioxaanthracene 32; heterocycles with fused tetrahydropyran rings. These ring systems populate predominantly the conformation in which the oxygen atoms are in a gauche arrangement. The tricycle 31 is a rigid derivative of 14‐crown‐3 and, as in the case of 12‐crown‐3, it forms complexes with lithium ions in acetonitrile.

ChemInform Abstract: Stereoselective Synthesis of Alcohols. Part 49. Tetrahydro‐4‐pyranols and 4‐Piperidinols by Intramolecular Allylboration Reaction.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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.

Stereoselective Synthesis of Alcohols, XLIX. Tetrahydro‐4‐pyranols and 4‐Piperidinols by Intramolecular Allylboration Reaction

Abstracttrans‐ and cis‐3‐Vinyltetrahydropyran‐4‐ol (11) and (12) as well as derivatives of trans‐ and cis‐3‐vinyl‐4‐piperidinol (25) and (33) were synthesized by essentially stereospecific intramolecular allylboration reactions: The (Z)‐allylboronates 15 and 32 were converted into the cis‐disubstituted heterocycles the (E)‐allylboronates 9 and 23 into the trans‐disubstituted heterocycles.

ChemInform Abstract: Cis‐Fused Di‐ and Tritetrahydropyrans by Intramolecular Allylboration Reactions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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.

Cis-Fuseddi- and tri-tetrahydropyrans by intramolecular allylboration reactions

A one pot procedure is described, in which ω-oxo-γ-alkoxyallylboronates 8 are generated from ω-allyloxy-aldehydes 9 and cyclized to cis-disubstituted vinyltetrahydropyranols 4. Repetition of this procedure on the allyloxyaldehyde 11 led to the cis-syn-cis-di-tetrahydropyranol 12, and on to the cis-syn-cis-syn-cis-tri-tetrahedropyranol 15.

ChemInform Abstract: Synthesis of Oxo‐2‐alkenylboronates and Their Cyclization to 3‐ Methylene Cycloalkanols via Intramolecular Allylboration.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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.

Synthesis of oxo-2-alkenylboronates and their cyclization to 3-methylene cycloalkanols via intramolecular allylboration

The cross-coupling reaction between halocarbonyl compounds with Knochel's (dialkoxyboryl)methylzinc reagent provided a new synthesis of oxoalk-2-enylboronates; the in situ cyclization of these boronates gave 3-methylene cyclopentanols or cycloheptanols in high yields.

Stereoselective Synthesis of Alcohols, XLIII. Asymmetric Induction on the Intramolecular Allylboration Reaction of (8‐Oxo‐2‐octenyl)boronates

AbstractThe cyclization of (8‐oxo‐2‐octenyl)boronates having methyl substituents in the chain linking the two functional groups proceeds with complete simple diastereoselectivity and with induced diastereoselectivity of 85 to > 98% to give methylsubstituted 2‐vinylcyclohexanols.