Cyclic acetylenes

Fukuzawa A, Masamune T (1981) Laurepinnacin and isolaurepinnacin, new acetylenic cyclic ethers from the marine red alga Laurenciapinnata Yamada. Tetrahedron Lett 22 4081 1084 Fukuzawa A, Kurosawa E, Tobetsu I (1979) Constituents of marine plants. XXXVI. Laurallene, new bromoallene from the marine red alga Laurencia nipponica yamada. Tetrahedron Lett 30 2797-2780... 

Laurepinnacin (23) and isolaurepinnacin (24) are acetylenic cyclic ethers from the red alga Laurencia pinnata Yamada that demonstrate insecticidal activity.47 Z-laureatin (25), Z-isolau-reatin (26), and deoxyprepacifenol (27) are other related compounds from the red alga... 

Mihopoulos N, Vagias C, Scoullos M, Roussis V (1999) Laurencienyne B, a New Acetylenic Cyclic Ether from the Red Alga Laurencia obtusa. Nat Prod Lett 13 151... 

Acetophenone, A/-methyloxazolidine derivative, lithiation, 56, 261 Acetyl hypofluorite fluorination of uracil by, 59, 3 fluorination using, 60, 7 reaction with pyridines, 58, 280, 289 Acetylacetone, hexafluoro-, reaction with ethylenediamine, 56, 3 Acetylene cyclic dimer, trimer. tetramer, dissociation energies, 56, 343 Acetylenes, activated reactions with 3-diazo-azoles, 59, 70... 

Mihopoulos, N., Vagias, C., Scouflos, M., and Roussis, V. (1999) Laurencienyne B, a new acetylenic cyclic ether from the red alga Laurencia obtusa. Nat. Prod. Lett., 13,151-156. 

All natural organobromocompounds are of marine origin and have been found especially in algae. The genus Laurencia has provided a series of brominated acetylenic cyclic ethers and bromosesquiterpenes, two of which, aplysin and aplysinol, were isolated earlier from the sea hare, Aplysia kurodai. Reviews by Scheuer 160) and Premuzic (752) may be consulted and also the more recent papers 87, 93, 102, 103, 107, 128, 129, 130). A brominated bicyclic diterpenoid, aplysin-20, with unusual stereochemical features has been also isolated from Aplysia kurodai 186), and more recently unique brominated and chlorinated monoter-penes have been obtained from A. californica 85) 86). Two of them were also found as components of an extract of the alga Plocamium coccineum... 

In stereoselective antitheses of chiral open-chain molecules transformations into cyclic precursors should be tried. The erythro-configurated acetylenic alcohol given below, for example, is disconnected into an acetylene monoanion and a symmetrical oxirane (M. A. Adams, 1979). Since nucleophilic substitution occurs with inversion of configuration this oxirane must be trens-conilgurated its precursor is commercially available trans-2-butene. 

Hydrocarbons that contain a carbon-carbon triple bond are called alkynes Non cyclic alkynes have the molecular formula C H2 -2 Acetylene (HC=CH) is the simplest alkyne We call compounds that have their triple bond at the end of a carbon chain (RC=CH) monosubstituted or terminal alkynes Disubstituted alkynes (RC=CR ) have internal triple bonds You will see m this chapter that a carbon-carbon triple bond is a functional group reacting with many of the same reagents that react with the double bonds of alkenes... 

Methyl ketones are important intermediates for the synthesis of methyl alkyl carbinols, annulation reagents, and cyclic compounds. A common synthetic method for the preparation of methyl ketones is the alkylation of acetone derivatives, but the method suffers limitations such as low yields and lack of regioselectivity. Preparation of methyl ketones from olefins and acetylenes using mercury compounds is a better method. For example, hydration of terminal acetylenes using HgSO gives methyl ketones cleanly. Oxymercuration of 1-olefins and subsequent oxidation with chromic oxide is... 

The above cycloaddition process consists of two separate [3-1-2] cycloaddition steps and represents a 1,3-2,4 addition of a multiple bond system to a hetero-1,3-diene [7S7]. The structure ot the azomethine imine intermediate has been proved unequivocally by X-ray analysis [195] Ethylene [194], acetylene [/iS2] . many alkyl- and aryl- as well sgemmal dialkyl- and diaryl-substituted alkenes [196,197, 198, 199], dienes [200], and alkynes [182, 201], certain cyclic alkenes [198, 199,... 

A two-carbon ring expansion of cyclic ketones was achieved by the addition of acetylenic esters and diesters to the enamine derivatives of the ketones, and reported almost simultaneously from several laboratories (337-343). The intermediate bicyclic adduct could be isolated in some cases. 

Figure A Cyclic oligomerizations of acetylene tetramerization producing cyclooctatetraene (cot) and trimerization producing benzene.

Reversible interaction of the carbonyl group with an azine lone-pair (cf. 245) should facilitate substitution adjacent to the heteroatom by the anion of a )3-hydroxyethyl ketone. A similar cyclic intermediate (246) is presumably responsible for the cyclization of acetylene dicarboxylic esters with azines. Similar cyclic intermediates... 

Dithiatopazine 73 serves as a sulfur-transfer reagent under thermal conditions. Tlius, heating 73 and diene 130 in toluene at 100°C formed a cyclic disulfide 131 (25%) and a tetrasulfide 132 (28%) with the formation of the alkene 118 (90%). Under similar conditions, the highly strained acetylene 133 was converted to the 1,2-dithiete 134 (65%) and the congested thiophene 135 (12%) (90JA3029). 

The Pauson-Khand reaction was originally developed using strained cyclic alkenes, and gives good yields with such substrates. Alkenes with sterically demanding substituents and acyclic as well as unstrained cyclic alkenes often are less suitable substrates. An exception to this is ethylene, which reacts well. Acetylene as well as simple terminal alkynes and aryl acetylenes can be used as triple-bond component. 

Fig. 14. Amplitude dependences (y0 is the amplitude of cyclic deformations) of the elastic modulus for frequency a) = 63 s 1 13% dispersion of acetylene carbon black in low- (/) and high-molecular (2) poly(isobutylene)s...

A second consequence of the cyclic transition state of these reactions is that (Z)-alkenyl-stannanes are less reactive than their (E)-isomers and can in some cases be recovered unchanged from reactions in which mixtures of isomers are used109. a-Alkoxy-2-butenylstannanes fail to react with 0,/J-dialkylated a./J-unsaturated aldehydes, on heating, and give low syn/anli stereoselectivity with ,/i-acetylenic aldehydes, perhaps because of reduced steric effects110. 

The N-aminoaziridine version7 of the a,/3-epoxyketone->alkynone fragmentation is a possible alternative in situations where the simple tosylhydrazone version6-9 fails. The tosylhydrazone method often gives good yields at low reaction temperatures, but it tends to be unsuccessful with the epoxides of enones that are not cyclic or are not fully substituted at the /5-carbon atom. For example, it has been reported9 that 2,3-epoxycyclohexanone docs not produce 5-hexynal by the tosylhydrazone route. The A-aminoaziridine method can also be recommended for the preparation of acetylenic aldehydes as well as ketones. 

A derivative of cyclopentyne has been trapped in a matrix. Although cycloheptyne and cyclohexyne have not been isolated at room temperatures, Pt(0) complexes of these compounds have been prepared and are stable." The smallest cyclic allene" so far isolated is l-/err-butyl-l,2-cyclooctadiene 107." The parent 1,2-cyclooctadiene has not been isolated. It has been shown to exist transiently, but rapidly dimerizes." " The presence of the rert-butyl group apparently prevents this. The transient existence of 1,2-cycloheptadiene has also been shown," and both 1,2-cyclooctadiene and 1,2-cycloheptadiene have been isolated in platinum complexes." 1,2-Cyclohexadiene has been trapped at low temperatures, and its structure has been proved by spectral smdies." Cyclic allenes in general are less strained than their acetylenic isomers." The cyclic cumulene 1,2,3-cyclononatriene has also been synthesized and is reasonably stable in solution at room temperature in the absence of air." ... 

Similar reactions have been carried out on acetylene. Aldehydes add to alkynes in the presence of a rhodium catalyst to give conjugated ketones. In a cyclic version of the addition of aldehydes, 4-pentenal was converted to cyclopen-tanone with a rhodium-complex catalyst. In the presence of a palladium catalyst, a tosylamide group added to an alkene unit to generate A-tosylpyrrolidine derivatives. ... 

Cyclic a,p-unsaturated ketones can be cleaved by treatment with base of their epoxy tosylhydrazone derivatives to give acetylenic ketones. The reaction can be applied to the formation of acetylenic aldehydes (R=H) by using the corresponding, 2,4-dinitrotosylhydrazone derivatives.Hydrazones (e.g., 47) prepared from... 

Diederich F, Gobbi L (1999) Cyclic and Linear Acetylenic Molecular Scaffolding. 201 43-79... 

The secondary orbital interaction has been applied to explain enantioselective catalytic Diels-Alder reactions of cyclic dienes and acetylenic dienophiles [23, 24]. 

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