Oct-l-yne

Addition of the P—H bond of hydrogen phosphonates (R0)2P(0)H across alkynes (hydrophosphorylation) may be catalyzed using both Pd° and Pd11 complexes.196 Reaction of oct-l-yne with either (MeO)2P(0)H or (EtO)2P(0)H affords the Markovnikoff adduct (Equation (18)) as the... 

The rate of oxidative coupling is said to decrease with decreasing acidity of the ethynyl hydrogen. Thus oct-l-yne underwent only limited reaction after being heated with the reagent under reflux for 24 hours. 

The l,3- dipolar cycloaddition of alkynes to anhydro-5-hydroxyoxazolium hydroxides leads to pyrroles (equation 66). Electron-withdrawing substituents in the alkyne are activating and DMAD reacts 48 times faster with compound (235) than does methyl propiolate, which in turn is 7000 times more reactive than oct-l-yne. The reaction has many ramifications and it is frequently used to trap unisolable munchnones with or without substituents on the nitrogen atom by an in situ reaction in which the betaine is generated in the presence of the dipolarophile (equation 67). It has become an important method for constructi ng the pyrrole ring of fused heterocyclic systems, as in the example of equation (68). 

Figure 12-8 compares the IR spectra of oct-l-yne and oct-4-yne. In addition to the alkane absorptions, the oct-l-yne spectrum shows sharp peaks at 3313 and 2119 cm-1. The absorption at 3313 cm-1 results from stretching of the stiff = C—H bond formed by the sp hybrid alkyne carbon. The 2119 cm-1 absorption results from stretching of the C=C triple bond. 

Nitrile triple bond stretching absorptions are at slightly higher frequencies (and usually more intense) than those of alkyne triple bonds. Compare this spectrum of butyronitrile with that of oct-l-yne in Figure 12-8. 

These titanium compounds can be described as an alkene 7r-complex or a metallacyclopropane, which is of practical importance. According to several computational studies, it has been concluded that the alkene titanium complexes are best represented as titanacyclopropane derivatives. The synthesis of titanium-alkyne complexes Ti(Me3SiC=CG6H13)(OR)2 from reaction between l-(trimethylsilyl)oct-l-yne with achiral or chiral alkoxo titanium compounds Ti(OR)4 has been described (Scheme 95).184 A series of organotitanium compounds (Scheme 96) are obtained by metathesis reactions.41... 

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