Acyclic alkynals

Sheppard N and De La Cruz C 1998 Vibrational spectra of hydrocarbons adsorbed on metals. Part II. Adsorbed acyclic alkynes and alkanes, cyclic hydrocarbons including aromatics and surface hydrocarbon groups derived from the decomposition of alkyl halides, etc Adv. Catal. 42 181-313... 

A few publications have appeared concerning the metathesis of alkynes so far only heterogeneous systems with acyclic alkynes have been reported (31-33). From experiments with [l-14C]2-hexyne this reaction was found to be analogous to the metathesis of alkenes, because it turned out to be a transalkylidynation reaction (33) ... 

Part II. Adsorbed Acyclic Alkynes and Alkanes, Cyclic Hydrocarbons Including Aromatics, and Surface Hydrocarbon Groups Derived from the Decomposition of Alkyl Halides, etc. 

A particularly interesting example is the synthesis of alkyne-bridged oligomers and polymers, which are attractive materials for optical and electronic applications. Bunz and coworkers were able to modify the Mortreux catalyst system [Mo(CO)6 and a suitable phenol]11 and reaction conditions to perform acyclic alkyne metathesis of 1,4-dipropynylated benzenes to produce high-molecular-weight poly(p-... 

Table 22 Lactonization of Acyclic Alkynic Acids (Equation 76)...

The Claisen-type condensation reaction of cyclic vinylogous carboxylic acid triflates with lithium enolates and their analogues has provided acyclic alkynes bearing a 1,3-diketone-type moiety.19 The reaction mechanism has been proposed to proceed via a 1,2-addition of the enolate to the vinylogous acyl triflate, followed by fragmentation of the aldolate intermediate (Scheme 2). 

Synthesis, reactions, and physical properties of stable mononuclear platinum and zirconium complexes of cyclohexyne reported prior to the late 1980s have been comprehensively covered in earlier reviews.2-8 More recently, reaction of the zirconocene complex of cyclohexyne with trimethyla-luminum and trimethylgallium has been reported to give 247 and 248, respectively [Eq. (36)].57-58 These products are novel because four atoms (carbons Cl and C3, the transition metal, and the main group metal) are covalently bonded to an sp2 hybridized carbon (C2) in a planar tetracoordi-nate fashion. Synthesis of this type of complex, which Erker describes as anti-van t Hoff/LeBel, does not require the strained cycloalkyne ring zirconocene complexes of acyclic alkynes react similarly.57-58... 

The first isolated and fully characterized zirconacyclopropene prepared by the reaction of free alkyne and ZrCp2 is (46 equation 41 Figure 1). Independently and simultaneously, another X-ray structure of an acyclic alkyne-zirconocene (47) prepared as shown in equation (42) was also published. The first X-ray structure of a zirconacyclopropane derivative is shown in Figure 2. ... 

Propargylic oxidation of the acyclic alkyne (5.126) can be achieved with moderate enantioselectivity. It is noteworthy that in this case, the quoted yield is based on the starting material (rather than being based on the perester).One drawback with this procedure is the very slow reaction rate. It has been discovered that the rate of the oxidation can be enhanced using phenylhydrazine as an additive, to aid in the reduction of Cu(II) to Cu(I), and Cu-PYBOX ligand (5.127) as catalyst. 

Figure 12.28 Conversion of strained cyclooctyne to the acyclic alkyne product can be conveniently monitored by NMR. ...

Alkynes (Sections 2.1, 2.1C, 4.1, and 4.6) Hydrocarbons having at least one triple bond between carbon atoms. Acyclic alkynes have the general formula CnH2n -2- Monocyclic alkynes have the general formula of CnH2n +4. Alkynes are said to be unsaturated because C = C triple bonds can react to add two molecules of hydrogen to the molecule, yielding an alkane. 

A series of optically active acyclic alkyne oligomers 77 (Fig. 21) crmtaining two to nine tmits of (7 )-71 and bearing decyloxycarbonyl side chains have been synthesized [71]. In chloroform, heptamer (n = 7), octamer (n = 8), and nonamer n = 9) form helical and dimeric structures, most likely double helices, whereas the lower oligomers form random-coil structures. Heptamer gradually unfolds to a random-coil structure in chloroform at room temperature. 

When other electrophiles besides a,/ff-unsaturated ketones are used, the mechanism is analogous, however, care must be taken to ensure that direct desilylation of acyclic intermediate 31, to form acyclic alkyne 32 does not occur. It is interesting that the use of more sterically encumbered alkylsilanes, for example tert-butyldimethylsilyl rather than trimethylsilyl, increases the selectivity of the reaction for the cyclized product versus the acyclic alkyne 32 that is produced by desilylation of silylvinyl cation 31. ... 

The use of other electrophiles in the Danheiser annulation for the formation of cyclopentenes is relatively unexplored. Ynones have been reported to imdergo cycloaddition, although examples are limited. Thus treatment of butynone 64 with silyl allene 47 under the usual conditions delivered cyclopentadiene 65 in 53% yield. Danheiser has reported that nitroalkenes do not provide annulation products furnishing instead acyclic alkynes. For example, treatment of nitroalkene 66 with silylallene 34 under standard conditions gives alkyne 67 rather than the cyclopentene 68. afi-Unsaturated aldehydes have been reported to be problematic, failing to provide isolable cyclopentene products. Treatment of methacrolein (69) with silylallene 34 under the standard conditions produced only a complex mixture of unidentified products. 

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