1.4- Enynes acetylene derivative

Addition of diazo compounds to 1,3-enynes Gyclopropanes from ethyiene derivatives Pyrazoles from acetylene derivatives... 

Ethylmagnesium bromide cuprous cyanide Synthesis of 1,4-enynes from acetylene derivs. 

A characteristic feature of contemporary investigations in the held under consideration, is the interest in cycloaddition reactions of nitrile oxides with acetylenes in which properties of the C=C bond are modified by complex formation or by an adjacent metal or metalloid atom. The use of such compounds offers promising synthetic results. In particular, unlike the frequently unselec-tive reactions of 1,3-enynes with 1,3-dipoles, nitrile oxides add chemo-, regio-and stereoselectively to the free double bond of (l,3-enyne)Co2(CO)6 complexes to provide 5-alkynyl-2-oxazoline derivatives in moderate to excellent yield. For example, enyne 215 reacts with in situ generated PhCNO to give 80% yield of isoxazoline 216 (372). 

Scheme 6.49 Intramolecular dehydro Diels-Alder reactions of conjugated enynes with a remote acetylene subunit furnishing annulated benzene derivatives, according to Danheiser and co-workers.

S)-(-)-CITRONELLOL from geraniol. An asymmetrically catalyzed Diels-Alder reaction is used to prepare (1 R)-1,3,4-TRIMETHYL-3-C YCLOHEXENE-1 -CARBOXALDEHYDE with an (acyloxy)borane complex derived from L-(+)-tartaric acid as the catalyst. A high-yield procedure for the rearrangement of epoxides to carbonyl compounds catalyzed by METHYLALUMINUM BIS(4-BROMO-2,6-DI-tert-BUTYLPHENOXIDE) is demonstrated with a preparation of DIPHENYL-ACETALDEHYDE from stilbene oxide. A palladium/copper catalyst system is used to prepare (Z)-2-BROMO-5-(TRIMETHYLSILYL)-2-PENTEN-4-YNOIC ACID ETHYL ESTER. The coupling of vinyl and aryl halides with acetylenes is a powerful carbon-carbon bond-forming reaction, particularly valuable for the construction of such enyne systems. 

Alkynes and ynamines have also been developed as useful participants in RCM approaches to pyrrolidine derivatives (Scheme 13). Mori and co-workers reported the formation of a cyclic dienamide via ene-ynamide RCM <020L803>. They also studied substituent effects on the course of RCM of enynes and reported the formation of both pyrrolidines and piperidines <02MI678>. The syntheses of 5- and 6-ring carbocycles and O-containing heterocycles from appropriate precursors were also reported in that work. Synthetically-useful dienylboronic acids have been prepared from acetylenic boronates <00AG(E)3101>. ... 

Diynes.4 A general method for preparation of 1,3-diynes, particularly terminal ones, involves palladium-catalyzed coupling of alkynylzinc derivatives with (E)-l-iodo-2-chloroethylene. This alkene is obtained in 83% yield by reaction of acetylene with iodine monochloride in 6N HC1. Coupling results in a 1-chloro-l, 3-enyne (1), which is converted into a l-sodio-l,3-diyne (2), which in turn can be reduced or alkylated to give a 1,3-diyne. 

Such cumulenic derivatives cannot be obtained by isomerization of acetylenic precursors under catalytic conditions, since they are thermodynamically less stable than the acetylenes. Special conditions for the protonation of metallated acetylenic sulfides and metallated enyne amines are described in Refs. [7] and [106] and in Chap. IV, Exp. 19. 

Alkyne metathesis is generally restricted to internal alkynes, and is driven to completion by the evolution of gaseous 2-butyne. Representative examples of alkyne cross-metathesis are depicted in Scheme 33, and include (i) dimerization of alkynylbenzoic acid derivative 287, (ii) alkyne cross-metathesis of 289 and bis(trimethylsilyl)acetylene, (iii) cross-metathesis of enyne 291 and various alkynes and metathesis dimerization of 291, and (iv) formation of high molecular weight alkyne-containing polymers through acyclic diyne metathesis (ADIMET) polymerization of acyclic diynes (e.g., 293) " using the molybdenum hexacarbonyl/2-chlorophe-nol system. 

General Synthesis.—Terminal acetylenes can be transformed into carboxylic acids by conversion into the trimethylsilyl derivatives followed by addition of a dialkyl-borane and oxidative hydrolysis (Scheme 1). Conjugated enynes can undergo a similar conversion, and yields throughout are high. 

The Conia-ene reaction of P-ketoesters bearing a pendant triple bond involves the cycloisomerization of an enyne formed by enolization. This transformation is efficiently catalyzed by cationic gold(I) complexes and afforded cyclopentane derivatives with excellent yields and moderate to good diastereoselectivities (Scheme 4-40). Acetylenic silyl enol ethers or imines react in an analogous manner. By this method, iodoalkynes were converted into iodocyclopentenes, which are highly useful in natural product synthesis. 

Substitution of the ethylenic carbons in a conjugated enyne by either an electropositive group in the 3-position or by an electronegative group in the 4-position favors addition to the acetylenic group. G. F. Bettinetti, G. Desimoni, and P. Griinanger, G. 94, 91 (1964) cyclopropane ring from ethylene derivatives in methanol s. F. Wessely and A. Eitel, M. 95, 1577 (1964). 

Condensation of y-(trialkylsilyl)allylboranes and allenylboranes with simple aldehydes and conjugated allenic, acetylenic, and enynyl aldehydes followed by a stereoselective elimination of trialkylsilanol produced 1,3-butadienes, diene-allenes, enyne-allenes, enediynes, and dienediynes with high isomeric purity. The trimethyltin chloride-induced transformations of 1-alkynyltrialkylborates also provided easy access to a variety of unsaturated compounds. High energy intermediates, such as o-isotoluenes, biradicals, o-quinodimethanes, benzocyclobutadienes, and enyne-ketenes, were derived from these unsaturated molecules for subsequent synthetic elaborations. 

Further work from Vollhardt s group on cobalt-catalysed cycloadditions of olefins and acetylenes has led to a synthesis of cyclohexadiene derivatives (188 n = 0—2) by addition of trimethyl silylacetylenes the reactions can also be carried out in an intramolecular sense, leading to tricyclic compounds. The novel tricyclic compound (189) has been obtained from naphthoquinone by a [2 + 2]addition of l,l-bis(silylmethyl)ethylene followed by treatment with a Lewis acid. A key step in the first total synthesis of a decipiene diterpene is the formation of tricyclic ketone (190) by an intramolecular aldol condensation, which required the use of methanolic barium oxide. ... 

Alkenes s. Ethylene derivatives Alkenynes s. Enynes Alkoxyacetylenes (s. a. l-Alkoxy-4-hydroxy-acetylenes)... 

The reaction of 1,6-enynes with secondaiy phosphine oxides under appropriate conditions resulted in the formation of phosphinoyl-fluorene derivatives as the end product. The addition of the >P(0)H species to the acetylenic moiety was followed by two intramolecular cyclizations (Scheme 36). ... 

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