π‐Stacked hydrogen‐bonded dimers in 2‐(2‐nitro­phenyl­amino­carbonyl)­benzoic acid,and hydrogen‐bonded sheets in orthorhombic and monoclinic polymorphs of 2‐(4‐nitro­phenyl­amino­carbonyl)­benzoic acid

Molecules of 2‐(2‐nitrophenylaminocarbonyl)benzoic acid, C₁₄H₁₀N₂O₅, are linked into centrosymmetric R(8) dimers by a single O—H⋯O hydrogen bond [H⋯O = 1.78 Å, O⋯O = 2.623 (2) Å and O—H⋯O = 178°] and these dimers are linked into sheets by a single aromatic π–π stacking interaction. The isomeric compound 2‐(4‐nitrophenylaminocarbonyl)benzoic acid crystallizes in two polymorphic forms. In the orthorhombic form (space group P2₁2₁2₁ with Z′ = 1, crystallized from ethanol), the mol­ecules are linked into sheets of R(22) rings by a combination of one N—H⋯O hydrogen bond [H⋯O = 1.96 Å, N⋯O = 2.833 (3) Å and N—H⋯O = 171°] and one O—H⋯O hydrogen bond [H⋯O = 1.78 Å, O⋯O = 2.614 (3) Å and O—H⋯O = 173°]. In the monoclinic form (space group P2₁/n with Z′ = 2, crystallized from acetone), the mol­ecules are linked by a combination of two N—H⋯O hydrogen bonds [H⋯O = 2.09 and 2.16 Å, N⋯O = 2.873 (4) and 2.902 (3) Å, and N—H⋯O = 147 and 141°] and two O—H⋯O hydrogen bonds [H⋯O = 1.84 and 1.83 Å, O⋯O = 2.664 (3) and 2.666 (3) Å, and O—H⋯O = 166 and 174°] into sheets of some complexity. These sheets are linked into a three‐dimensional framework by a single C—H⋯O hydrogen bond [H⋯O = 2.45 Å, C⋯O = 3.355 (4) Å and C—­H⋯O = 160°].     

Intermolecular interactions in the chiral and racemic forms of 3‐­hydroxy‐2‐(1‐oxoisoindolin‐2‐yl)­butanoic acid derived from threonine

The title compounds, C₁₂H₁₃NO₄, are derived from l ‐threonine and dl ‐threonine, respectively. Hydro­gen bonding in the chiral derivative, (2S/3R)‐3‐hydroxy‐2‐(1‐oxoisoindolin‐2‐yl)­butanoic acid, consists of O—H_acid?O_alkyl—H?O=C_indole chains [O?O 2.659 (3) and 2.718 (3) Å], Csp³—H?O and three C—H?π_arene interactions. In the (2R,3S/2S,3R) racemate, conventional carboxylic acid hydrogen bonding as cyclical (O—H?O=C)₂ [graph set R₂²(8)] is present, with O_alkyl—H?O=C_indole, Csp³—H?O and C—H?π_arene interactions. The COOH group geometry differs between the two forms, with C—O, C=O, C—C—O and C—C=O bond lengths and angles of 1.322 (3) and 1.193 (3) Å, and 109.7 (2) and 125.4 (3)°, respectively, in the chiral structure, and 1.2961 (17) and 1.2210 (18) Å, and 113.29 (12) and 122.63 (13)°, respectively, in the racemate structure. The O—C=O angles of 124.9 (3) and 124.05 (14)° are similar. The differences arise from the contrasting COOH hydrogen‐bonding environments in the two structures.     

Preparation of Pd(PPh<Subscript>2</Subscript>H)<Subscript>2</Subscript>(PPh<Subscript>3</Subscript>)<Subscript>2</Subscript> and its Role as a Precursor of a Dinuclear Complex with Bridging Phosphide Ligands

Reaction of PPh₂H with Pd(PPh₃)₄ in a 4:1 molar ratio produced the Pd complex with two diphenylphosphine ligands, Pd(PPh₂H)₂(PPh₃)₂ (1). Complex (1) was characterized by n.m.r. (¹H and ³¹P{¹H}) spectra as well as by elemental analysis. Reaction of (1) with RhCl(PPh₃)₃ yielded a Pd–Rh heterobimetallic complex with bridging phosphide ligands, formulated as [(Ph₃P)₂Pd(μ-PPh₂)₂Rh(PPh₃)₂]Cl (2).     

Three isomeric forms of hydroxyphenyl‐2‐oxazoline: 2‐(2‐hydroxyphenyl)‐2‐oxazoline, 2‐(3‐hydroxyphenyl)‐2‐oxazoline and 2‐(4‐hydroxyphenyl)‐2‐oxazoline

Crystal structures are reported for three isomeric compounds, namely 2‐(2‐hydroxy­phenyl)‐2‐oxazoline, (I), 2‐(3‐hydroxy­phenyl)‐2‐oxazoline, (II), and 2‐(4‐hydroxy­phenyl)‐2‐oxazoline, (III), all C₉H₉NO₂ [systematic names: 2‐(4,5‐dihydro‐1,3‐oxazol‐2‐yl)phenol, (I), 3‐(4,5‐dihydro‐1,3‐oxazol‐2‐yl)phenol, (II), and 4‐(4,5‐dihydro‐1,3‐oxazol‐2‐yl)phenol, (III)]. In these compounds, the deviation from coplanarity of the oxazoline and benzene rings is dependent on the position of the hydroxy group on the benzene ring. The coplanar arrangement in (I) is stabilized by a strong intra­molecular O—H⋯N hydrogen bond. Surprisingly, the 2‐oxazoline ring in mol­ecule B of (II) adopts a ³T₄ (^C2T_C3) conformation, while the 2‐oxazoline ring in mol­ecule A, as well as that in (I) and (III), is nearly planar, as expected. Tetra­mers of mol­ecules of (II) are formed and they are bound together via weak C—H⋯N hydrogen bonds. In (III), strong inter­molecular O—H⋯N hydrogen bonds and weak intra­molecular C—H⋯O hydrogen bonds lead to the formation of an infinite chain of mol­ecules perpendicular to the b direction. This paper also reports a theoretical investigation of hydrogen bonds, based on density functional theory (DFT) employing periodic boundary conditions.     

2′‐De­oxy‐2‐fluoro­tubercidin

In the title compound [systematic name: 7‐(2‐de­oxy‐β‐d ‐erythro‐pentofuranos­yl)‐2‐fluoro‐7H‐pyrrolo[2,3‐d]pyrimidin‐2‐amine], C₁₁H₁₃FN₄O₃, the conformation of the N‐glycosylic bond is between anti and high‐anti [χ = −110.2 (3)°]. The 2′‐deoxy­ribofuranosyl unit adopts the N‐type sugar pucker (₄T³), with P = 40.3° and τ_m = 39.2°. The orientation of the exocyclic C4′—C5′ bond is −ap (trans), with a torsion angle γ = −168.39 (18)°. The nucleobases are arranged head‐to‐head. The crystal structure is stabilized by four inter­molecular hydrogen bonds of types N—H⋯N, N—H⋯O and O—H⋯O.     

The 7‐bromo derivative of 2‐amino‐2′‐deoxytubercidin fluorinated at the sugar moiety

The title compound, 2,4‐diamino‐5‐bromo‐7‐(2‐deoxy‐2‐fluoro‐β‐d ‐arabinofuranosyl)‐7H‐pyrrolo[2,3‐d]pyrimidine, C₁₁H₁₃BrFN₅O₃, shows two conformations of the exocyclic C4′—C5′ bond, with the torsion angle γ (O5′—C5′—C4′—C3′) being 170.1 (3)° for conformer 1 (occupancy 0.69) and 60.7 (7)° for conformer 2 (occupancy 0.31). The N‐glycosylic bond exhibits an anti conformation, with χ = −114.8 (4)°. The sugar pucker is N‐type (C3′‐endo; ³T₄), with P = 23.3 (4)° and τ_m = 36.5 (2)°. The compound forms a three‐dimensional network that is stabilized by several intermolecular hydrogen bonds (N—H...O, O—H...N and N—H...Br).     

Aktivierung von Schwefelkohlenstoff an Trirutheniumclustern: Synthese und Kristallstruktur von [Ru3(CO)5(μ‐H)2(μ‐PCy2)(μ‐Ph2PCH2PPh2){μ‐η2‐PCy2C(S)}(μ3‐S)] und [Ru3(CO)5(CS)(μ‐H)(μ‐PtBu2)(μ‐PCy2)2(μ3‐S)]

Activation of Carbon Disulfide on Triruthenium Clusters: Synthesis and X‐Ray Crystal Structure Analysis of [Ru₃(CO)₅(μ‐H)₂(μ‐PCy₂)(μ‐Ph₂PCH₂PPh₂){μ‐η²‐PCy₂C(S)}(μ₃‐S)] and [Ru₃(CO)₅(CS)(μ‐H)(μ‐P^tBu₂)(μ‐PCy₂)₂(μ₃‐S)] [Ru₃(CO)₆(μ‐H)₂(μ‐PCy₂)₂(μ‐dppm)] ( 1 ) (dppm = Ph₂PCH₂PPh₂) reacts under mild conditions with CS₂ and yields by oxidative decarbonylation and insertion of CS into one phosphido bridge the opened 50 VE‐cluster [Ru₃(CO)₅(μ‐H)₂(μ‐PCy₂)(μ‐dppm){μ‐η²‐PCy₂C(S)}(μ₃‐S)] ( 2 ) with only two M–M bonds. The compound 2 crystallizes in the triclinic space group P 1 with a = 19.093(3), b = 12.2883(12), c = 20.098(3) Å; α = 84.65(3), β = 77.21(3), γ = 81.87(3)° and V = 2790.7(11) ų. The reaction of [Ru₃(CO)₇(μ‐H)(μ‐P^tBu₂)(μ‐PCy₂)₂] ( 3 ) with CS₂ in refluxing toluene affords the 50 VE‐cluster [Ru₃(CO)₅(CS)(μ‐H)(μ‐P^tBu₂)(μ‐PCy₂)₂(μ₃‐S)] ( 4 ). The compound cristallizes in the monoclinic space group P 2₁/a with a = 19.093(3), b = 12.2883(12), c = 20.098(3) Å; β = 104.223(16)° and V = 4570.9(10) ų. Although in the solid state structure one elongated Ru–Ru bond has been found the complex 4 can be considered by means of the ³¹P‐NMR data as an electron‐rich metal cluster.     

(2‐Amino­ethoxy)­bis(2‐thienyl)­boron

In the five‐membered ring in the title compound, (2‐amino­ethoxy)­bis(2‐thienyl)­boron, C₁₀H₁₂BNOS_2, the B atom is four‐coordinate with dimensions N—B 1.654 (3), O—B 1.479 (3), and C—B 1.606 (3) and 1.609 (3) Å. An intermolecular hydrogen bond between an amino H atom and the ethoxy O atom links the mol­ecules into infinite chains along the a axis. Only one of the two amino H atoms is involved in hydrogen bonding because there is only the one acceptor atom, the ethoxy O atom, and the molecular geometry precludes formation of a second hydrogen bond by the second amino H atom.     

2′‐Deoxy‐5‐fluorotubercidin

In the title compound, 4‐amino‐7‐(2‐deoxy‐β‐d ‐erythro‐pentofuranosyl)‐5‐fluoro‐7H‐pyrrolo[2,3‐d]pyrimidine, C₁₁H₁₃FN₄O₃, the conformation of the glycosyl bond lies between anti and high anti [χ = −101.1 (3)°]. The furanose moiety adopts the S‐type sugar pucker (²T₃), with P = 164.7 (3)° and τ = 40.1 (2)°. The extended structure is a three‐dimensional hydrogen‐bond network involving a C—H⋯F, two N—H⋯O and two O—H⋯O hydrogen bonds.     

A series of substituted (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐phenylprop‐2‐en‐1‐ones

In the molecular structures of a series of substituted chalcones, namely (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐phenylprop‐2‐en‐1‐one, C₂₁H₁₅FO₂, (I), (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐(4‐fluorophenyl)prop‐2‐en‐1‐one, C₂₁H₁₄F₂O₂, (II), (2E)‐1‐(4‐chlorophenyl)‐3‐(2‐fluoro‐4‐phenoxyphenyl)prop‐2‐en‐1‐one, C₂₁H₁₄ClFO₂, (III), (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐(4‐methylphenyl)prop‐2‐en‐1‐one, C₂₂H₁₇FO₂, (IV), and (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐(4‐methoxyphenyl)prop‐2‐en‐1‐one, C₂₂H₁₇FO₃, (V), the configuration of the keto group with respect to the olefinic double bond is s‐cis. The molecules pack utilizing weak C—H...O and C—H...π intermolecular contacts. Identical packing motifs involving C—H...O interactions, forming both chains and dimers, along with C—H...π dimers and π–π aromatic interactions are observed in the fluoro, chloro and methyl derivatives.     

Intramolecular Photocyclization of 2‐Acylphenyl Methacrylates: a Convenient Access to 4,5‐Dihydro‐1,4‐epoxy‐2‐benzoxepin‐3(1H)‐ones (= Benzo[c]‐6,8‐dioxabicyclo[3.2.1]octan‐7‐ones

The photochemical reactions of 2‐acylphenyl methacrylates (= 2‐acylphenyl 2‐methylprop‐2‐enoates) 1 were investigated. Irradiation of 2‐acylphenyl methacrylates 1a – d in MeCN gave the tricyclic lactones 2a – d in good yields, together with a small amount of O CO bond cleavage product, the 2‐acylphenols 3a – d (Scheme 2, Table). The formation of the tricyclic lactones 2 probably follows a mechanism involving a 1,7‐diradical through ζ‐H abstraction (1,8‐H transfer) by the excited carbonyl O‐atom (Scheme 3). Irradiation of 2‐acylphenyl tiglate (= 2‐acylphenyl (2E)‐2‐methylbut‐2‐enoate) 1e and 2‐acylphenyl methacrylates 1g – i , substituted by a MeO group (δ‐H) at the 3,5‐positions of the phenyl group, also gave the tricyclic lactones 2e and 2g – i , but in low yields. On the other hand, no H‐abstraction products were observed on irridation of 2‐(ethoxycarbonyl)phenyl methacrylate 1f , of 2‐acylphenyl methacrylate 1j which is substituted by a Me group (γ‐H) at the 3,5‐positions of the phenyl group, and of 1k with an OH group at the 3‐position of the phenyl group.     

A novel heterometallic dinuclear compound: rac‐pentaaqua‐1κ5O‐(μ‐2‐sulfidoacetato‐1:2κ3O:O′,S)bis(2‐sulfidoacetato‐2κ2O,S)manganese(II)tin(IV)

The title racemic heterometallic dinuclear compound, [MnSn(C₂H₂O₂S)₃(H₂O)₅], (I), contains one main group Sn^IV metal centre and one transition metal Mn^II centre, and, by design, links the Mn^II centre to the building unit of the (Δ/Λ) [SnL₃]²⁻ complex anion (L is the 2‐sulfidoacetate dianion). In this cluster, the Sn^IV centre of the (Δ/Λ) [SnL₃]²⁻ unit is coordinated by three O atoms and three S atoms from three L ligands to form an [SnO₃S₃] octahedral coordination environment. The Mn^II centre is in an [MnO₆] octahedral coordination environment, with five O atoms from five water molecules and the sixth from the μ₂‐L ligand of the (Δ/Λ) [SnL₃]²⁻ unit. Between adjacent dinuclear molecules, there are many hydrogen‐bond interactions of O—H...O, O—H...S, C—H...O and C—H...S types. Of these, eight pairs of O—H...O hydrogen bonds fuse all the dinuclear molecules into two‐dimensional supramolecular sheets along the bc plane. Adjacent supramolecular sheets are further connected through O—H...S hydrogen bonds to give a three‐dimensional supramolecular network.     

3,3a‐Dihydrocyclo­penta­[b]­chromen‐1(2H)‐ones from the reaction of salicylaldehyde and 2‐cyclo­penten‐1‐one

The two title chromene compounds, 3,3a‐dihydrocyclo­penta­[b]chromen‐1(2H)‐one, C₁₆H₁₂O₂, (I), and 2‐(2‐hydroxy­benzyl­idene)‐3,3a‐dihydrocyclo­penta­[b]chromen‐1(2H)‐one, C₁₉H₁₄O₃, (II), have been determined in the monoclinic space group P2₁/n. Compound (I) is mainly stabilized by C—H⋯π inter­actions. Compound (II) is linked into infinite one‐dimensional chains with a C(3) motif via inter­molecular O—H⋯O hydrogen bonds. The inter­molecular C—H⋯π and π–­π inter­actions also play key roles in stabilizing the crystal packing. Two intra­molecular C—H⋯O hydrogen bonds with S(5) motifs were detected in (II).     

The diastereoisomers 2‐[(S/R)‐2‐chloro‐3‐quinolyl]‐2‐[(R)‐1‐(4‐methoxyphenyl)ethylamino]acetonitrile at 100 K

In the structures of the two enantiopure diastereoisomers of the title compound, C₂₀H₁₈ClN₃O, which crystallize in different space groups, the molecules are very similar as far as bond distances and angles are concerned, but more substantial differences are observed in some torsion angles. The crystal structures of both molecules can be described as zigzag layers along the c axis. The packing is stabilized by hydrogen‐bond interactions of N—H...O, C—H...Cl and C—H...π types for 2‐[(R)‐2‐chloro‐3‐quinolyl]‐2‐[(R)‐1‐(4‐methoxyphenyl)ethylamino]acetonitrile, and of N—H...N, C—H...O and C—H...π types for 2‐[(S)‐2‐chloro‐3‐quinolyl]‐2‐[(R)‐1‐(4‐methoxyphenyl)ethylamino]acetonitrile, resulting in the formation of two‐ and three‐dimensional networks.     

Preparation of β2‐Homotryptophan Derivatives for β‐Peptide Synthesis

In view of the prominent role of the 1H‐indol‐3‐yl side chain of tryptophan in peptides and proteins, it is important to have the appropriately protected homologs H‐β² HTrp OH and H‐β³ HTrp OH (Fig.) available for incorporation in β‐peptides. The β²‐HTrp building block is especially important, because β²‐amino acid residues cause β‐peptide chains to fold to the unusual 12/10 helix or to a hairpin turn. The preparation of Fmoc and Z β²‐HTrp(Boc) OH by Curtius degradation (Scheme 1) of a succinic acid derivative is described (Schemes 2–4). To this end, the (S)‐4‐isopropyl‐3‐[(N‐Boc‐indol‐3‐yl)propionyl]‐1,3‐oxazolidin‐2‐one enolate is alkylated with Br CH₂CO₂Bn (Scheme 3). Subsequent hydrogenolysis, Curtius degradation, and removal of the Evans auxiliary group gives the desired derivatives of (R)‐H β²‐HTrp OH (Scheme 4). Since the (R)‐form of the auxiliary is also available, access to (S)‐β²‐HTrp‐containing β‐peptides is provided as well.     

Concomitant polymorphism in the stereoselective synthesis of a β‐benzyl‐β‐hydroxyaspartate analogue

Two concomitant polymorphs, (I) and (II), of a β‐benzyl‐β‐hydroxyaspartate analogue [systematic name: dibenzyl 2‐benzyl‐2‐hydroxy‐3‐(4‐methylphenylsulfonamido)succinate], C₃₂H₃₁NO₇S, crystallize from a mixture of ethyl acetate and cyclohexane at ambient temperature. The structure of (I) has triclinic (P) symmetry and that of (II) monoclinic (P2₁/c) symmetry. Both crystal structures are made up of a stacking of homochiral racemic dimers (2S,3S and 2R,3R) which are internally connected by a similar R₂²(9) hydrogen‐bonding pattern consisting of intermolecular N—H...O and O—H...O hydrogen bonds. The centroid of the racemic dimer lies on an inversion centre. The main structural difference between the two polymorphs is the conformational orientation of two of the four aromatic rings present in the molecule. Polymorph (II) is found to be twinned by reticular merohedry with twin index 3 and twin fractions 0.854 (1) and 0.146 (1).     

[2‐(2‐Pyridyl)‐1H‐benzimidazole‐κ2N2,N3]bis(p‐toluato‐κ2O,O′)manganese(II)

In the title compound, [Mn(C₈H₇O₂)₂(C₁₂H₉N₃)], the manganese(II) centre is surrounded by three bidentate chelating ligands, namely, one 2‐(2‐pyridyl)benzimidazole ligand [Mn—N = 2.1954 (13) and 2.2595 (14) Å] and two p‐toluate ligands [Mn—O = 2.1559 (13)–2.2748 (14) Å]. It displays a severely distorted octahedral geometry, with cis angles ranging from 58.87 (4) to 106.49 (5)°. Intermolecular C—H...O hydrogen bonds between the p‐toluate ligands link the molecules into infinite chains, and every two neighbouring chains are further coupled by N—H...O and C—H...O hydrogen bonds between the 2‐(2‐pyridyl)benzimidazole and p‐toluate ligands, leading to an infinite ribbon‐like double‐chain packing mode. The complete solid‐state structure can be described as a three‐dimensional supramolecular framework, stabilized by these intermolecular hydrogen‐bonding interactions and possible C—H...π interactions, as well as stacking interactions involving the 2‐(2‐pyridyl)benzimidazole ligands.     

Structural comparison of group 7 tricarbonyl complexes of 2‐{[2‐(1H‐imidazol‐4‐yl)ethyl]iminomethyl}‐5‐methylphenolate

Two tricarbonyl complexes of rhenium(I) and manganese(I) coordinated by the ligand 2‐{[2‐(1H‐imidazol‐4‐yl)ethyl]iminomethyl}‐5‐methylphenolate are reported, viz. fac‐tricarbonyl(2‐{[2‐(1H‐imidazol‐4‐yl‐κN³)ethyl]iminomethyl‐κN}‐5‐methylphenolato‐κO)rhenium(I) methanol monosolvate, [Re(C₁₆H₁₄N₃O₄)(CO)₃]·CH₃OH, (I), and fac‐tricarbonyl(2‐{[2‐(1H‐imidazol‐4‐yl‐κN³)ethyl]iminomethyl‐κN}‐5‐methylphenolato‐κO)manganese(I), fac‐[Mn(C₁₆H₁₄N₃O₄)(CO)₃], (II), display facial coordination in a distorted octahedral environment. The crystal structure of (I) is stabilized by O—H...O, N—H...O and C—H...O hydrogen‐bond interactions, while that of (II) is stabilized by N—H...O hydrogen‐bond interactions only. These interactions result in two‐dimensional networks and π–π stacking for both structures.     

μ3‐η2:η2:η2‐Coordination of Primary Silane on a Triruthenium Plane

A μ₃‐η²:η²:η²‐silane complex, [(Cp*Ru)₃(μ₃‐η²:η²:η²‐H₃SitBu)(μ‐H)₃] ( 2 a ; Cp*=η⁵‐C₅Me₅), was synthesized from the reaction of [{Cp*Ru(μ‐H)}₃(μ₃‐H)₂] ( 1 ) with tBuSiH₃. Complex 2 a is the first example of a silane ligand adopting a μ₃‐η²:η²:η² coordination mode. This unprecedented coordination mode was established by NMR and IR spectroscopy as well as X‐ray diffraction analysis and supported by a density functional study. Variable‐temperature NMR analysis implied that 2 a equilibrates with a tautomeric μ₃‐silyl complex ( 3 a ). Although 3 a was not isolated, the corresponding μ₃‐silyl complex, [(Cp*Ru)₃(μ₃‐η²:η²‐H₂SiPh)(H)(μ‐H)₃] ( 3 b ), was obtained from the reaction of 1 with PhSiH₃. Treatment of 2 a with PhSiH₃ resulted in a silane exchange reaction, leading to the formation of 3 b accompanied by the elimination of tBuSiH₃. This result indicates that the μ₃‐silane complex can be regarded as an “arrested” intermediate for the oxidative addition/reductive elimination of a primary silane to a trinuclear site.     

Studies towards the Synthesis of Alkyl N‐(4‐Nitrophenyl)‐3/2‐oxomorpholine‐2/3‐carboxylates

The syntheses of methyl 4‐(4‐nitrophenyl)‐3‐oxomorpholine‐2‐carboxylate ( 3a ) and ethyl 4‐(4‐nitrophenyl)‐2‐oxomorpholine‐3‐carboxylate ( 5b ), important building blocks for the synthesis of factor Xa inhibitor rivaroxaban analogs with potential dual antithrombotic activity, via Rh₂(OAc)₄‐catalyzed O? H and N? H carbene insertion reactions are described.