Lipase‐Catalyzed Dynamic Kinetic Resolution of C1‐ and C2‐Symmetric Racemic Axially Chiral 2,2′‐Dihydroxy‐1,1′‐biaryls

We have discovered that the racemization of configurationally stable, axially chiral 2,2′‐dihydroxy‐1,1′‐biaryls proceeds with a catalytic amount of a cyclopentadienylruthenium(II) complex at 35–50 °C. Combining this racemization procedure with lipase‐catalyzed kinetic resolution led to the first lipase/metal‐integrated dynamic kinetic resolution of racemic axially chiral biaryl compounds. The method was applied to the synthesis of various enantio‐enriched C₁‐ and C₂‐symmetric biaryl diols in yields of up to 98 % and enantiomeric excesses of up to 98 %, which paves the way for new developments in the field of asymmetric synthesis.     

Substituent Effects on the Blue—Shifting Hydrogen Bonds between X—C≡C—CF2—H and Water

MP2／6－31 g(d) calculations were performed verifying the existences of blue-shifting X-C≡C-CF2-H…OH2 hydrogen bonds.Detailed analyses revealed that the interaction energy and donor-acceptor distance had good correlations with the substituent Hammett constants.However,the extent of C-H bond contraction and the blue shift of the C-H stretching vibration did not show any good correlation with the traditional substituent constants,indicating that certain more complicated mechanisms might be involved in the present systems.Nevertheless,it was found that highly electron-with-drawing susbtituents were not favorable to the C-H bond contraction,and it was suggested that the attractive interaction between water and the carbon of -CF2H probably played an important role in the blue shift.     

Iridium‐Catalyzed Direct C4‐ and C7‐Selective Alkynylation of Indoles Using Sulfur‐Directing Groups

Indoles and their analogues have been one of the most ubiquitous heterocycles during the past century, and extensive studies have been conducted to establish practical synthetic methods for their derivatives. In particular, selective functionalization of the poorly reactive benzenoid core over the pyrrole ring has been a great challenge. Reported herein is an iridium‐catalyzed direct alkynylation of the indole C4‐ and C7‐positions with the assistance of sulfur directing groups. This transformation shows a wide range of functional‐group tolerance with exceptional site selectivity. The directing group can be either easily removed or transformed after catalysis. The synthetic utility of the alkyne fragment is demonstrated by the derivatization into the core structure of natural indole alkaloids.     

Syntheses of β‐C(1→3)‐Glucopyranosides of 2‐ and 4‐Deoxy‐D‐hexoses

The Oshima? Nozaki (Et₂AlI) condensation of isolevoglucosenone ( 4 ) with 2,6‐anhydro‐3,4,5,7‐tetra‐O‐benzyl‐D ‐glycero‐D ‐gulo‐heptose ( 5 ) gave an enone 6 that was converted with high stereoselectivity to 3‐C‐[(1R)‐2,6‐anhydro‐D ‐glycero‐D ‐gulo‐heptitol‐1‐C‐yl]‐2,3‐dideoxy‐D ‐arabino‐hexose ( 1 ; 1 : 1 mixture of α‐ and β‐D ‐pyranose), and to 3‐C‐[(1R)‐2,6‐anhydro‐D ‐glycero‐D ‐gulo‐heptitol‐1‐C‐yl]‐2,3‐dideoxy‐D ‐lyxo‐hexose ( 2 ; 2.7 : 1.4 : 1.0 : 1.4 mixture of α‐D ‐furanose, β‐D ‐furanose, α‐D ‐pyranose, and β‐D ‐pyranose). The Oshima? Nozaki (Et₂AlI) condensation of levoglucosenone ( 17 ) with aldehyde 5 gave an enone 18 that was converted with high stereoselectivity to 3‐C‐[(1R)‐2,6‐anhydro‐D ‐glycero‐D ‐gulo‐heptitol‐1‐C‐yl]‐3,4‐dideoxy‐α‐D ‐arabino‐hexopyranose ( 3 ; single anomer).     

1,2‐Ph2‐9‐I‐1,2‐closo‐C2B10H9

The title compound, 9‐iodo‐1,2‐di­phenyl‐1,2‐dicarba‐closo‐dodecaborane(9), C₁₄H₁₉B₁₀I, has the expected pseudo‐icosahedral cluster geometry, with a cage C—C distance of 1.724 (4) Å, comparable to that in the non‐iodinated parent. However, the twist angles, θ, of the phenyl rings are 2.1 (6) and 27.6 (5)°, the latter being unusually large.     

Palladium‐catalyzed regioselective C2‐arylation of 5‐aminoindole

Pd(II)‐catalyzed C‐H arylations of 5‐aminoindole using iodobenzenes as aryl source was studied. Despite pivalamide directing group at 5‐position of the indole, the direct C2‐arylation of the indole observed in high yields and with high regioselectivity.     

Catalytic Enantioselective Synthesis of C1‐ and C2‐Symmetric Spirobiindanones through Counterion‐Directed Enolate C‐Acylation

A catalytic enantioselective route to C₁‐ and C₂‐symmetric 2,2′‐spirobiindanones has been realized through an intramolecular enolate C‐acylation. This reaction employs a chiral ammonium counterion to direct the acylation of an in situ generated ketone enolate with a pentafluorophenyl ester. This reaction constitutes the first example of a direct catalytic enantioselective C‐acylation of a ketone and provides an efficient and highly enantioselective route to axially chiral spirobiindanediones. These products can be diastereoselectively derivatized, offering access to a range of functionalized spirocyclic architectures.     

Formation of Fluorinated Amido Esters through Unexpected C3−C4 Bond Fission in 4‐Trifluoromethyl‐3‐oxo‐β‐lactams

4‐Trifluoromethyl‐3‐oxo‐β‐lactams were unexpectedly transformed into 2‐[(2,2‐difluorovinyl)amino]‐2‐oxoacetates as major products, accompanied by minor amounts of 2‐oxo‐2‐[(2,2,2‐trifluoroethyl)amino]acetates, upon treatment with alkyl halides and triethylamine in DMSO. This peculiar C3?C4 bond fission reactivity was investigated in‐depth, from both an experimental and a computational point of view, in order to shed light on the underlying reaction mechanism.     

Synthesis and 1H and 13C NMR structural analysis of cis‐ and trans‐2‐imino‐1,3‐ and ‐3,1‐perhydrobenzoxazines and their 3‐ and 1‐N‐methyl derivatives

cis‐ and trans‐2‐imino‐1,3‐ and ‐3,1‐perhydrobenzoxazines and the N‐methyl derivatives of the latter were synthesized from the corresponding cyclic 1,3‐amino alcohol with cyanogen bromide. The configurations of the studied compounds were confirmed by ¹H and ¹³C NMR spectra. All trans‐fused compounds exist in biased chair–chair conformations as expected, whereas the cis‐fused 1,3‐benzoxazines attain exclusively the O‐in conformations. The cis‐fused 3,1‐benzoxazines, especially the 1‐methyl‐substituted derivatives, tend to favor the N‐out form, obviously owing to the favorable axial orientation of this N‐methyl. Copyright © 2003 John Wiley & Sons, Ltd.     

Structural Basis and Enzymatic Mechanism of the Biosynthesis of C9‐ from C10‐Monoterpenoid Indole Alkaloids

Cutting carbons : The three‐dimensional structure of polyneuridine aldehyde esterase (PNAE) gives insight into the enzymatic mechanism of the biosynthesis of C₉‐ from C₁₀‐monoterpenoid indole alkaloids (see scheme). PNAE is a very substrate‐specific serine esterase. It harbors the catalytic triad S87‐D216‐H244, and is a new member of the α/β‐fold hydrolase superfamily. Its novel function leads to the diversification of alkaloid structures.

     

Bipodal 1,1′‐acyl‐3,3,3′,3′‐tetraalkylbis(thiourea) ligands with flexible C3, C4 and C6 spacer groups

In the structures of 3,3,3′,3′‐tetraethyl‐1,1′‐(propane‐1,3‐diyldicarbonyl)bis(thiourea), C₁₅H₂₈N₄O₂S₂, (I), 3,3,3′,3′‐tetraethyl‐1,1′‐(butane‐1,4‐diyldicarbonyl)bis(thiourea), C₁₆H₃₀N₄O₂S₂, (II), and 3,3,3′,3′‐tetrabutyl‐1,1′‐(hexane‐1,6‐diyldicarbonyl)bis(thiourea), C₂₆H₅₀N₄O₂S₂, (III), compound (I) displays resonance‐assisted hydrogen bonding, (II) exhibits an inversion centre, and both (II) and (III) are characterized by intermolecular hydrogen bonds between the carbonyl O atoms and thioamide H atoms, leading to chains of hydrogen‐bonded molecules throughout the structures. The accurate structural data for these molecules is expected to assist in molecular modelling and other studies currently in progress.