Fritsch Buttenberg Wiechell Research Articles

Use of 1-chlorovinyl p-tolyl sulfoxides as alkynylmagnesium chloride sources

A method for generating alkynylmagnesium chlorides from 1-chlorovinyl p-tolyl sulfoxides and an isopropylmagnesium chloride–lithium chloride complex (turbo Grignard reagent) has been developed. The method consists of a sulfoxide/magnesium exchange reaction of 1-chlorovinyl p-tolyl sulfoxides and a turbo Grignard reagent, a Fritsch–Buttenberg–Wiechell rearrangement of the resulting magnesium alkylidene carbenoids, and a deprotonation of terminal alkynes with a turbo Grignard reagent. The resulting alkynylmagnesium chlorides are reacted with a variety of electrophiles to generate internal alkynes.

Fritsch-Buttenberg-Wiechell rearrangement of magnesium alkylidene carbenoids leading to the formation of alkynes.

A series of 1-heteroatom-substituted vinyl p-tolyl sulfoxides were prepared and treated with organometallic reagents to evaluate which combination of sulfoxides and organometallic reagents yielded alkynes the most efficiently. The use of 1-chlorovinyl p-tolyl sulfoxide and isopropylmagnesium chloride was optimal for this purpose. A variety of 1-chlorovinyl p-tolyl sulfoxides were prepared from carbonyl compounds and chloromethyl p-tolyl sulfoxide and were converted into alkynes via the sulfoxide/magnesium exchange reaction and subsequent Fritsch–Buttenberg–Wiechell (FBW) rearrangement of the resulting magnesium alkylidene carbenoids. The mechanism of the FBW rearrangement of magnesium alkylidene carbenoids was studied by using 13C-labeled sulfoxides and by using DFT calculations.

α‐Hydroxy‐Tetrazoles as Latent Ethynyl Moieties: A Mechanistic Investigation

This article focuses on the dehydration of α‐hydroxy‐tetrazoles, leading to tetraazafulvenes and then to vinylic carbenes that rearrange into ethynyl moieties through the Fritsch–Buttenberg–Wiechell rearrangement. Each step of this sequence was scrutinized, either by examination of the substrate and/or dehydrating agent scope, or through AM1 calculations, in order to understand the limiting step of this process. This underrated transformation appears to be a viable alternative to existing methods used for transforming aldehydes into alkynes.

Effect of Transition Metal Fragments on the Reverse Fritsch-Buttenberg-Wiechell Type Ring Contraction Reaction of Metallabenzynes to Metal-Carbene Complexes.

Metallabenzynes (1M), contrary to their organic analogues, benzynes, undergo ring-contraction to metal-carbene complexes (2M) via a reverse Fritsch-Buttenberg-Wiechell (FBW) type rearrangement. A detailed computational quantum mechanical study has been carried out to understand the effect of different third row transition metal fragments (ML2L'2; M = W, Re, Os, Ir, Pt; L/L' = PH3, Cl, CO) on the stability of metallabenzynes and their reactivity toward reverse FBW type rearrangement. Our results indicate that the late transition metal fragments Ir(PH3)Cl3 and PtCl4 prefer 16 VE metal-carbene complex (2M), while the middle transition metal fragments W(PH3)4, Re(PH3)3Cl, and Os(PH3)2Cl2 prefer metallabenzyne (1M). This can be attributed to the reduced overlap between the transition metal fragment ML2L'2 and organic fragment C5H4 in metallabenzyne 1M when M changes from W to Pt. Furthermore, the presence of a π-accepting ligand CO on the metal fragment makes the conversion of 1M to 2M more feasible.

Na2S-mediated synthesis of terminal alkynes from gem-dibromoalkenes.

The Na2S-mediated facile synthesis of terminal alkynes from gem-dibromoalkenes, at 20/40 °C under open flask conditions has been developed. Various precursors derived from heteroaromatic/aromatic/aliphatic aldehydes were found compatible. The reaction is proposed to proceed through the Fritsch-Buttenberg-Wiechell (FBW) rearrangement involving the corresponding vinyl carbene. Using mild reaction conditions with inexpensive Na2S·9H2O under air atmosphere has significant advantages over earlier routes.

Ring expansion and vinylic nucleophilic substitution competing for (tert-alkyl)2C[dbnd]C(Li)–Cl in carbenoid chain processes

Vinylic nucleophilic substitution (SNV) reactions of unactivated, cyclic α,α-dichloroalkenes [(tert-alkyl)2CCCl2] with aryllithiums (RLi) to give (tert-alkyl)2CC(Cl)–R are presented to be carbenoid chain reactions, which involve the unsaturated Cl,Li-carbenoids (tert-alkyl)2CC(Li)–Cl as transient intermediates. The chains are longer and the overall reactions much slower in tert-butyl methyl ether (t-BuOMe) than in THF as the solvent. In competition with the fast SNV step of these Cl,Li-carbenoids, the Fritsch–Buttenberg–Wiechell (FBW) ring expansion in t-BuOMe (but less so in THF) generates short-lived cyclohexyne species, which are trapped by the accompanying RLi species to yield chlorocyclohexene derivatives [(tert-alkyl)–(Cl)CC(R)–(tert-alkyl)] as the FBW chain products.

Phosphorus Version of the Fritsch-Buttenberg-Wiechell Reaction

Utilizing phosphorus version of the Fritsch-Buttenberg-Wiechell (FBW) reaction, arylphosphaalkynes are prepared from 2,2-dihalo-1-aryl-1-phosphaalkenes, and theoretical calculations were carried out to obtain some basic insight into intramolecular rearrangement in the phosphorus system of interest. [Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental resource: Density functional theory (DFT) and ab initio MP2 calculations.] [Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfer, and Silicon for the following free supplemental files: Additional tables, figures, and references.]

Synthesis of gem-dihaloenynes and butatrienes from gem-dihalovinyl derivatives

gem-Dihaloenynes were synthesized in high yields from 1,1,4,4-tetrahalo-1,3-butadienes through the Fritsch–Buttenberg–Wiechell (FBW) rearrangement mediated by an organolithium compound. Butatriene derivatives could be obtained efficiently via an organolithium-mediated reaction of o-halo-(2,2-dihalovinyl)benzenes.

ChemInform Abstract: Fritsch—Buttenberg—Wiechell Rearrangement to Alkynes from gem‐Dihaloalkenes with Lanthanum Metal.

AbstractThe first Fritsch—Buttenberg—Wiechell rearrangement of gem‐dihaloalkenes towards alkynes mediated by lanthanum metal and substoichiometric amounts of iodine is presented.

Adamantyl‐endcapped polyynes

Polyynes spanning from a diyne to a dodecayne with adamantyl endgroups have been synthesized using the Fritsch–Buttenberg–Wiechell rearrangement as a key step to construct the acetylenic framework. Molecular properties as a function of polyyne length have been analyzed by UV–Vis spectroscopy, cyclic voltammetry, differential scanning calorimetry, and X‐ray crystallography. Copyright © 2011 John Wiley & Sons, Ltd.

Fritsch–Buttenberg–Wiechell rearrangement to alkynes from gem-dihaloalkenes with lanthanum metal

The first example of the FBW rearrangement using of lanthanum metal and a catalytic amount of iodine was disclosed. When gem-diiodo- and gem-dibromoalkenes were treated with lanthanum metal in the presence of a catalytic amount of iodine, the reductive dehalogenation of these compounds smoothly proceeded to produce the corresponding alkynes in moderate to good yields.

Carbanionic Rearrangements of Halomethylenecyclobutanes. Stereochemistry of the Migrating Group

The unusual base-induced ring-enlargement of halomethylenecyclobutanes to 1-halocyclopentenes was examined with unsymmetrical and (13)C-labeled substrates to study regio- and stereochemical characteristics. Migration of a ring carbon atom (single migration) or simultaneous migration of a ring carbon atom and the halide (double migration) gives the ring-enlarged products. (13)C-labeling experiments established that both rearrangements occur with retention of configuration at the migrating center. These systems are suggested as models for the Fritsch-Buttenberg-Wiechell (FBW) rearrangement.

A Novel Synthetic Approach to Diaminoacetylenes: Structural Characterization and Reactivity of Aromatic and Aliphatic Ynediamines

Electron-rich diaminoalkynes with a variable substitution pattern can be conveniently prepared by lithiation of 2,2-dibromo-1,1-ethenediamines; the alkynes are formed by a Fritsch–Buttenberg–Wiechell rearrangement of intermediate LiBr–vinylidene species. The first two X-ray crystal structures of diaminoalkynes are presented, which show almost perpendicular orientations of the NC3 planes. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

ChemInform Abstract: Toward Carbyne: Synthesis and Stability of Really Long Polyynes

AbstractReview: 81 refs.

ChemInform Abstract: The Fritsch—Buttenberg—Wiechell Rearrangement: Modern Applications for an Old Reaction

AbstractReview: 130 refs.

ChemInform Abstract: Generation of Nucleophilic Chromium Acetylides from gem‐Trichloroalkanes and Chromium Chloride: Synthesis of Propargyl Alcohols.

Nucleophilic mixed chromium(II) and chromium(III) acetylides are generated from the smooth reduction of primary 1,1,1-trichloroalkanes with chromium(II) chloride in the presence of an excess amount of triethylamine at room temperature. These species arise from chromium(III) vinylidene carbenoids. It has been demonstrated that uncommon low-valent Cr II acetylides are formed by C―H insertion of Cr II Cl 2 into terminal alkynes, formed in situ through the Fritsch― Buttenberg―Wiechell (FBW) rearrangement, whereas Cr III acetylides are concomitantly generated by HCl elimination from the chromium(III) vinylidene carbenoid. Both divergent pathways result, overall, in the formation of nucleophilic acetylides. In situ trapping with electrophilic aldehydes afforded propargyl alcohols. Furthermore, deuteration experiments and the use of deuterium labeled 1,1,1-trichloroalkane substrates demonstrated the prevalence of low-valent Cr II acetylides, potentially useful, yet highly elusive synthetic intermediates.

Generation of Nucleophilic Chromium Acetylides from gem-Trichloroalkanes and Chromium Chloride: Synthesis of Propargyl Alcohols.

Nucleophilic mixed chromium(II) and chromium(III) acetylides are generated from the smooth reduction of primary 1,1,1-trichloroalkanes with chromium(II) chloride in the presence of an excess amount of triethylamine at room temperature. These species arise from chromium(III) vinylidene carbenoids. It has been demonstrated that uncommon low-valent Cr(II) acetylides are formed by C-H insertion of Cr(II)Cl(2) into terminal alkynes, formed in situ through the Fritsch- Buttenberg-Wiechell (FBW) rearrangement, whereas Cr(III) acetylides are concomitantly generated by HCl elimination from the chromium(III) vinylidene carbenoid. Both divergent pathways result, overall, in the formation of nucleophilic acetylides. In situ trapping with electrophilic aldehydes afforded propargyl alcohols. Furthermore, deuteration experiments and the use of deuterium labeled 1,1,1-trichloroalkane substrates demonstrated the prevalence of low-valent Cr(II) acetylides, potentially useful, yet highly elusive synthetic intermediates.

Toward carbyne: Synthesis and stability of really long polyynes

Molecules composed of sp-hybridized carbon chains (polyynes) are the simplest of the known conjugated organic oligomers. In comparison to their counterparts such as polyacetylene and polydiacetylene, however, the formation of polyynes has traditionally posed a difficult synthetic challenge. In particular, there is no reliable method to form end-capped polyethynylene, and monodisperse polyynes have therefore been assembled. As a result, structure–property relationships for shorter polyynes have been relatively well established in recent years, while extension of these trends toward longer polyynes has remained a difficult task. Using the Fritsch–Buttenberg–Wiechell (FBW) rearrangement, the formation of diynes through decaynes has become possible and has provided a unique chance to explore the physical characteristics of conjugated polyyne chains. This paper highlights recent advances in the synthesis of extended polyynes, as well as interesting aspects of their NMR, Raman, and UV/vis spectroscopic analyses. These synthetic achievements offer the opportunity to predict some of the properties of the carbon allotrope carbyne. In particular, a set of X-ray crystallographic analyses of t-Bu end-capped polyynes (tBu[n]) shows a definitive experimental trend in reduced bond-length alternation (BLA).

The Fritsch–Buttenberg–Wiechell rearrangement: modern applications for an old reaction

The Fritsch-Buttenberg-Wiechell rearrangement of carbene/carbenoid intermediates has evolved into a valuable synthetic methodology for the preparation of polyyne structures. Various synthetic routes toward the formation of the corresponding precursors, alkynyl-substituted dibromoolefins, have been developed. Additionally, the scope of this methodology is expanded significantly by the development of functional group-tolerant one-pot procedures. The preparation of various polyynes up to the octa- and decaynes is, thus, possible on a scale that enables thorough physico-chemical characterization. Hence, series of polyynes have been investigated by, e.g., UV-vis, IR- and Raman spectroscopy, as well as X-ray crystallography. These investigations give unique insight into the structural characteristics of longer polyynes and hint to the structure of carbyne.

Fritsch–Buttenberg–Wiechell (FBW) Reaction of 1-Halovinyllithium Carbenoids: A Computational Study

Abstract 1-Halovinyllithium carbenoids can undergo the Fritsch–Buttenberg–Wiechell (FBW) rearrangement to form alkynes. This reaction is quite facile when a hydrogen atom is present on carbon 2. The gas-phase reaction mechanism may consist of a single-step or several steps, depending on the aggregation state of the carbenoid. We examined the FBW reaction of 1-fluoro, chloro-, and bromovinyllithium in the monomer and two isomeric dimers. The migratory aptitude of the hydrogen atoms is dependent on the halogen and the aggregation state.