Macrocycles acetylenic

A simple, high yielding (65-90%) procedure has been described for the preparation of medium ring and macrocyclic acetylenic lactones which is mechanistically related to the well known Eschenmoser fragmentation reaction, and the following example is representative. Bromination of the tosylhydrazone of 1 was carried out with NBS at -10°C in a water/t-butanol/acetone mixture. The reaction mixture was then treated with aqueous NaHSC>3 solution and the resulting mixture heated at 50-60°C for one hour, which gave the acetylenic lactone 2. 

A novel Si-macrocycle was prepared by the demetalation of the zirconocene-containing dimeric cyclophane intermediate, which was formed by the coupling of dimethyl-fc(4-trimethylsilylethynylphenyl)silane with [Zr(Cp)2Cl2] <02CEJ74>. Synthesis, X-ray analysis, and characterization of a dibenzo macrocyclic acetylenic diphenylsilane have been reported <02TL2079>. 

Macrocyclic acetylenes containing one acetylenic linkage have been prepared by the oxidation of bishydrazones of macrocyclic 1,2-diones - >. This method has been used for the synthesis of 1,7-cyclododecadiyne starting from cyclododecyn-1,2-dione . 

Rubin, Y. Parker, T.C. Kahn S.I. Holliman, C.L. McElvany S.W. Precursors to endohedral metal fullerene complexes synthesis and x-ray structure of a flexible macrocyclic acetylenic cyclophane CgiH h- J. Am. Chem. Soc. 1996, 35(22), 5308-5309. 

Other interesting synthetic applications of the ketone-derived enamine alkylation are found in the monomethylation of steroid enamines (249), extension of the benzylation reaction (250) to a ferrocene derivative (251), the use of a-bromoesters (252) and ketones (252) or their vinylogues (25J), in the syntheses of alantolactone (254-256), isoalantolactone (257), and with a bridged bis-enamine (258). The use of bifunctional alkylating agents is also seen in the introduction of an acetylenic substituent in the synthesis of the characteristic fragrant constituent of jasmine (259), the synthesis of macrocyclic ketolactones (260), the use of butyrolactone (261), and the intermolecular or intramolecular double alkylations of enamines with dihalides (262). 

Apparently, the oxidative acetylene coupling can overcome a drastic strain increase as demonstrated by the highly efficient cyclization of octamethyltetra-deca-l,4,7,10,13-pentayne 36 and its perspirocyclopropanated analogue 61 to the corresponding 14-membered macrocycles 181 (67%) and 62 (45%), respectively (Scheme 34) [18]. 

Scott LT, Cooney M) (1995) Macrocyclic homoconjugated polyacetylenes. In Stang PJ, Diederich F (eds) Modern acetylene chemistry. VCH, Weinheim, p 321... 

The following is a comprehensive smwey of the chemistry of macrocycles comprised entirely of phenyl and acetylenic moieties. Although over fom" decades old, this area of research has come into its own just in the last few years. Widespread interest in the field has been spurred by recent discoveries utilizing these compoimds as ligands for organometallic chemistry, hosts for binding guest molecules, models of synthetic carbon allotropes, and precursors to fullerenes and other carbon-rich materials. This review will discuss the preparation of a tremendous variety of novel structm-es and detail the development of versatile synthetic methods for macro cycle construction. 

Over the last decade, the chemistry of the carbon-carbon triple bond has experienced a vigorous resurgence [1]. Whereas construction of alkyne-con-taining systems had previously been a laborious process, the advent of new synthetic methodology based on organotransition metal complexes has revolutionized the field [2]. Specifically, palladium-catalyzed cross-coupling reactions between alkyne sp-carbon atoms and sp -carbon atoms of arenes and alkenes have allowed for rapid assembly of relatively complex structures [3]. In particular, the preparation of alkyne-rich macrocycles, the subject of this report, has benefited enormously from these recent advances. For the purpose of this review, we Emit the discussion to cychc systems which contain benzene and acetylene moieties only, henceforth referred to as phenylacetylene and phenyldiacetylene macrocycles (PAMs and PDMs, respectively). Not only have a wide... 

An X-ray structure analysis of 74 (R=C4Hg) revealed that the unsaturated portion of the molecule was planar, with the angles between adjacent acetylenic bonds deviating by 13 -15° from 180°, the value for a strain-free molecule. Since the connection of the alkyne moieties to the aromatic rings was only shifted slightly (2-3°), distortion of the acetylene linkages appears as the major source of instability in these macrocycles. 

The penultimate example of macrocycles based on phenyl and acetylenic units has been the very recent report by Tobe [801 and Rubin [81] of cyclophane 134. Both groups generated 134 in the mass spectrometer by laser desorption of hexa-protected polyynes 135 (robust) and 136 (unstable), respectively (Scheme 31). 

Macrocyclic Structurally Homoconjugated Oligoacetylenes Acetylene-and Diacetylene-Expanded Cycloalkanes and Rotanes... 

An extensive computational analysis expanded the range of the c-d distances for reactive cyclic enediynes to 2.9-3.4 A.38 By comparing unsubstituted enediynes with dialkyl-substituted enediynes, it was found that the activation enthalpy is dependent on factors other than the c-d distance and that reactivity hinges on a subtle interplay of steric and electronic effects that accompany distortion caused by incorporation into a macrocycle. For example, since alkyl substituents stabilize acetylenic bonds to a greater extend than olefinic bonds,39 such substituents stabilize the starting material, thus increasing both the activation barrier and the reaction endothermicity. 

Macrocyclization,3 A new route to cembranolides (3) involves intramolecular coupling of an alkoxyallyltin derivative (1) with an acetylenic aldehyde catalyzed by BF30(C2H5)2 (cf. 12, 513-514). Thus in the presence of BF3 etherate 1 cyclizes to 2 with syn-selectivity. The product is converted to the cembranolide 3 by hydrolysis of the enol ether and oxidation. 

Squaraines 17b and 17c have terminal acetylene residues, which allowed to convert the squaraine dyes and tetralactam macrocycles into permanently interlocked rotaxane structures using copper-catalyzed and copper-free cycloaddition reactions with bulky stopper groups [58]. 

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