Acetylene adduct

Answer Amide disconnection gives chloroformate (7), made from alcohol (8) with COCl (cf p T37). Alcohol (8) is a simple acetylene adduct. 

T. Matsui, T. Morooka, and M. Nakayama, Preparation and structures of acetylene adducts of 4,6-O-isopropylidene- and 4-0-acetyl-6-0-triphenylmethyl-l,5-anhydro-2-deoxy-D-ejyt/wo-hex-l-en-3-uloses, Bull. Chem. Soc. Jpn., 60 (1987) 417—419. 

Azole approach. 5-JT[l,3,4]Thiadiazolo[3,2-a]pyridin-5-ones (723) can be prepared by 1,3-dipolar cycloaddition reactions between electron-deficient alkenic or alkynic dipolarophiles and the thiocarbonyl ylide dipole present in anhydro-5-hydroxy-2-methyl-6-phenylthiazolo[2,3-6][l,3,4]thiadiazolium hydroxide (720). Sulfur is extruded from the original acetylene adduct (722) whereas H2S is eliminated from the alkene adduct (721) to form the same product (723) (79JOC3808). 

The time is ripe for truly exciting developments in the reactivity of dinuclear transition metal compounds. The potential for cyclic sequences of reactions, as is required for catalytic reactions, has already been realized. (1) It has been shown, by Muetterties, et al. (53), that alkynes can be selectively hydrogenated to alkenes (cU 2H-addition) by Cp2Mo2(C0) the rate determining step involves CO dissociation from the acetylene adducts Cp2MO2(C0) (R2C2). (2) We have found that... 

Slater and Muetterties (28) have shown that the acetylene adducts, 4, undergo acetylene exchange above about 110°, and that complexes 4 react with H2 at 150-170° to produce 1 and cis-olefin (eq. 25). In the presence of excess H2 and acetylene, the process... 

Knox et al. (31) have also reported that cyclic 1,3-dienes react in a Diels-Alder fashion with the acetylene adduct, 4 (eq. 26). The Mo-Mo distance in 10 is 2.504(1)A, commensurate with a MosMo triple bond as required by the 18-electron rule. Acyclic dienes do not give 10, but with hexa-2,4-diene, 4 yields ethyne and the hexyne complex from the isomerized diene (eq. 27). 

The tranquilliser Oblivon (6) is clearly an acetylene adduct and the defoaming surfactant Surfynol (7) is clearly an acetylene diadduct. The... 

Otherwise few of these acetylene adducts are important in their own right, but they are valuable intermediates because disubstituted acetylenes (8) can be reduced to cis or trans alkenes at will and because monosubstituted acetylenes can be hydrated to methyl ketones (9). 

Other types of acetylene adduct (3) and (4) can also be hydrated but the ketone adducts (3) can give unexpected rearrangements. The simple adduct... 

Other types of acetylene adduct (3) and (4) can also be hydrated but the ketone adducts (3) can give unexpected rearrangements. Tbe simple adduct (26) hydrates as expected but the cyclic compound (27) dehydrates in the ring as well as being hydrated in the side chain. The useful product (28) is isomeric with (27),... 

Early studies have postulated oxyrene or cationic carbene intermediates in the formation of either green pigments or the acetic acid metabolites . In subsequent investigations, however, these intermediates were ruled out, based on structural and mechanistic consideration Ortiz de Montellano and coworkers observed that while there was a strong isotope effect in the formation of the acetic acid metabolite, there was no deuterium effect in the formation of the heme-acetylene adduct. The mechanism thus postulated by these authors for the formation of the green pigment as well as the acetic acid metabolites is compatible with the evidence available to date and is shown in Scheme 12. This mechanism... 

The readily prepared cobalt-stabilized cations (31) react with ketones, silyl enol ethers, and enol acetates to form, after decomplexation, the acetylenic adducts free from allenic by-products (Scheme 50). Quaternary centres can be generated by the use of suitably substituted cations. 

N. E. Kolobova, L. L. Ivanov, O. S. Zhvanko, V. F. Sizoi, and Yu. S. Nekrasov, Izv. Akad. Nauk SSSR, Ser. Khim., 1979, 2393. Syntheses of phosphorylide complexes of manganese. Complexes of type [Mn C(PPh3)CHC02MeKC0)2( j-C5H5)] prepared by addition of phosphine to acetylene adducts. 

The ground spin state of chromium (acetylene) adducts is known to be of quintet, and the most plausible reaction pathway on quintet surface needs to overcome two activation barriers to finish a single catalytic cycle, as depicted in Scheme 3.4. However, the reaction on quintet surface is prohibited by presenting a ffee-energy barrier of 31.1 kcal/mol that transforms two coordinated acetylene into the key intermediate 4D. Thus, the turnover of frequency (TOP) for the catalytic cycle on the quintet surface is 1.36 X 10 h, which rules out the quintet reaction mechanism for acetylene cyclotrimerization by Cr(II)/Si02 model catalyst. 

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