Alkyne derivatives intramolecular reactions

The benzene derivative 409 is synthesized by the Pd-catalyzed reaction of the haloenyne 407 with alkynes. The intramolecular insertion of the internal alkyne, followed by the intermolecular coupling of the terminal alkyne using Pd(OAc)2, Ph3P, and Cul, affords the dienyne system 408, which cyclizes to the aromatic ring 409[281]. A similar cyclization of 410 with the terminal alkyne 411 to form benzene derivatives 412 and 413 without using Cul is explained by the successive intermolecular and intramolecuar insertions of the two triple bonds and the double bond[282]. The angularly bisannulated benzene derivative 415 is formed in one step by a totally intramolecular version of polycycli-zation of bromoenediyne 414[283,284],... 

Intermolecular cyclotrimerization of alkynes using Wilkinson s catalyst has also afforded substituted carbazole derivatives. This reaction was extended to an intramolecular version by offering the possibility for a six-membered ring annotation that cannot be achieved easily in the corresponding intermolecular version. Intramolecular cyclotrimerization is completely regioselective due to an additional tether. 

The intramolecular version presents a very useful synthetic route to various polycyclic compounds. Even terminal alkenes give cyclopentenones in good yields, assisted by the addition of /V-methylmorpholine N-oxide (NMO) [85], The addition of trimethylamine A -oxidc also dramatically accelerates the reaction in the presence of oxygen, and both inter- and intramolecular reactions proceed at 0°C to room temperature [86]. The reaction was found to proceed rapidly at 25 °C by the addition of aqueous NH4OH [87]. Numerous applications to natural product syntheses have been reported. The tri- and tetracyclic skeletons 214 for crinipellin B, from 213 [88], and the triquinacene derivative 216, from 215, have been constructed [89,90], These results show that internal alkynes and terminal alkenes react smoothly in the intramolecular reactions. Domino reaction of the endiyne 217 produced the strained molecule of oxa[5.5.5.5]fenestrenedione (219) via 218 [91]. 

The intramolecular reaction can be extended to the cross-annulation reaction of aryl halides with unsaturated compounds [31,33]. For example, 2-halo-biphenyls react with alkynes to give phenanthrene derivatives [96,97]. By using the method, the analogs of hypericin known as antiviral agent (Eq. 45) [98] and indolocarbazoles (Eq. 46) [99] have been prepared. In these reactions, vinyl-palladium intermediates are involved. 

Simple alkynes do not undergo Intramolecular reactions with weakly electrophilic Iminium ions In the absence of strong external nucleophiles. For example, the formaldiminlum ion derived from 4-hexynylamine, formaldehyde, and... 

Since the targeted streptazolin-related natural products have a C2-unit at the C6-position, we first prepared the 2-oxazolone-alkyne derivative 82 with the simplest C2-unit, an ethyl group, at the triple bond terminus to not only identify suitable ring-closing conditions, but also to determine the level of stereoselectivity that could be expected in the intramolecular Pauson-Khand reaction. Thus, the 2-oxazolone-alkyne derivative 82, required for the intramolecular Pauson-Khand reaction in our retrosynthesis, was easily prepared from the known alcohol 78 by conventional means, as shown in Scheme 18. Oxidation of 78 was... 

They also studied the Pd(PPh3)4-catalyzed intramolecular reaction of an allene moiety with an alkyne in 1,5-alkyne-allene 140 in DMF in the presence of HCO2H affording cyclopentane derivatives 141 [36]. The reaction demonstrated an interesting solvent effect, i.e., the reaction in dioxane afforded a mixture of regioisomers referred to the C=C bond in 141 and 142 (Scheme 59). However, if the terminal alkyne was further substituted with the ethoxycarbonyl group,... 

---