Intramolecular with alkynes

Other 1,3-acyl migrations of propargylic carboxylates catalyzed by gold give intermediate allenes, which can afford heterocyclic compounds by intramolecular attack of the appropriate nucleophiles. The intermediate allenes formed by 1,3-acyl migrations can also react intramolecularly with alkynes to form naphthalenes, although this reaction proceeds more efficiently with Ag(I) catalysts, and is discussed in the aUcyne-carbon nucleophile section. 

Boronic acids react intramolecularly with alkynes in the presence of PPh3AuNTf2 as a catalyst to form synthetically useful boron enolates in excellent yields (Scheme 20) [150]. 

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],... 

Other examples of [2C+2S+1C0] cycloaddition reactions have been described by Herndon et al. by the use of chromium cyclopropyl(methoxy)carbenes. These complexes react with alkynes releasing ethene and forming cyclopenta-dienone derivatives, which evolve to cyclopentenone derivatives in the presence of chromium(O) and water [122] (Scheme 76). This reaction has been extended to intramolecular processes and also to the synthesis of some natural products [123]. These authors have also described another process involving a formal [2C+2S+1C0] cycloaddition reaction. Thus, the reaction of methyl and cyclo-propylcarbene complexes with phenylacetylene derivatives does not afford the expected benzannulated products, and several regioisomers of cyclopentenone derivatives are the only products isolated [124] (Scheme 76). 

This photodriven benzannulation was used in the synthesis of indolocar-bazoles (Eq. 22) [96] and calphostins (Eq. 23) [97]. The thermal insertion of isonitriles into these same classes of carbenes provided a complementary approach to similar benzannulations [98-100]. Manganese alkoxycarbene complexes underwent both inter- [101] and intramolecular [102] photodriven benzannulation reactions with alkynes (Eqs. 24 and 25). 

In another variant of these intramolecular 1,3-dipolar cycloadditions, the alkyne-containing amino acid amide 183, when reacted with acetic anhydride, produces a zwitterionic thiazolo-oxazolium intermediate, which may then react intramolecularly with the dipolarophile and give the triheterocycle 184 < 1999J(P 1) 1219, 2002JOC4045> (Equation 18). The benzo-fused analogue 185 is obtained similarly (Equation 19). 

Vinylketene complexes, generated by treatment of heteroatom-substituted carbene complexes with alkynes, can react intramolecularly with different nucleophiles to yield cyclic compounds (Figure 2.30, Table 2.20). Four- to ten-membered rings have... 

The reaction of alkoxy(alkyl)carbene chromium complexes with alkynes has been reported to give modest yields of cyclopentenones [368] and a few examples of intramolecular carbene C-H insertions of Fischer-type carbene complexes, leading to five-membered heterocycles, have been reported [369,370] (Table 2.22). 

In a one-pot procedure ortfto-bromoethynylbenzene, prepared by Pd-catalysed coupling of iodobromobenzene with alkynes, is converted into the ortfto-teUuroderivatives which suffer an intramolecular anft-hydrotelluration giving 1-benzoteUurophenes. ... 

As an extension of intermolecular reactions described earlier, some intramolecular lEDDA reactions of electron-deficient pyridazines with alkyne dienophiles have been presented <1998MOL10, 2001TL7929>. 

TABLE 2.41. INTRAMOLECULAR SILYL NITRONATE CYCLOADDITIONS WITH ALKYNES... 

Pd/tppts-catalysed intermolecular sp-sp couplings to afford diynes and sp2-sp coupling of 2-iodophenols or iodoanilines with alkynes followed by intramolecular cyclization to benzofurans and indoles, respectively, with moderate to good yields in H20/CH3CN solvent mixtures have also been described.517 8... 

Oxetanes can be formed by intramolecular reaction between a carbonyl group and an alkene, and this has been used (4.74) in making analogues of thromboxane A, (one of the compounds responsible for the control of blood clotting), albeit usually as the minor product. A special case of intramolecular reaction is seen for a,p-unsaturated carboxylic acids 14.75), where the product is an oxete that is tautomeric with a p-lactone. Oxetes may also be formed by photocycloaddition of ketones or aldehydes with alkynes the oxete normally ring-opens at room temperature to give an a,p-unsaturated carbonyl compound (4.76), but at lower temperatures its spectral... 

Benzazepinones can be prepared on cross-linked polystyrene by intramolecular Heck reaction (Entry 6, Table 15.35). In the presence of sodium formate, the intramolecular Heck reaction of iodoarenes with alkynes yields methylene benzazepinones (Entry 7, Table 15.35). Surprisingly, when this reaction was performed in solution, the main product (65% yield) was a dehalogenated, non-cyclized benzamide. In the synthesis on cross-linked polystyrene, however, this product was not observed [419]. 

Trialkylboranes generally show a low reactivity toward addition to alkenes and alkynes. Only trial-lylboranes react with alkynes under mild conditions. This reaction is often complicated by further intramolecular carboboration reactions and has found only limited synthetic application. 

A number of examples of photoaddition to alkynes has been described. Dimethyl acetylenedicarboxylate has been found to add to methyl-substituted 3-benzoylthiophens301 and to thiophen and 2,5-dimethylthiophen302 on irradiation. Benzo[f>]thiophen also undergoes cycloaddition reactions with alkynes,303 and in the case of dimethylacetylene dicarboxylate, product formation has been shown to be wavelength dependent.304 Intramolecular [ 2 -(- 2] cycloaddition has been observed on both direct and triplet-sensitized irradiation of the alkyne (353) and gives the cyclobutene (354)305 the isomer (355) is formed on prolonged irradiation. 

Intramolecular geometries, database studies, 1, 597 Intramolecular hydroalkoxylation, and etherification, 10, 672 Intramolecular pinacol coupling to cyclic 1,2-diols, 11, 51 with samarium reagents, 11, 60 Intramolecular silylformylation, alkynes and alkenes, 11, 489 Intramolecular solvomercuration alkenes, 2, 436 alkynes, 2, 439... 

Reaction of the carbene complex 148 with alkyne affords vinylcarbene 150 via metallacyclobutene 149. In the intramolecular reaction of enyne 152, catalysed by carbene complex 151, the triple bond is converted to vinylcarbene 153 which then reacts with the double bond to give the conjugated diene 154. Generation of 154 is expected by the formation and cleavage of cyclobutene 155 as a hypothetical intermediate. Based on this reaction, Ru-catalysed intramolecular metathesis of enyne 156 gave the N-containing cyclic diene 157, from which (—)-stemoamide (158) was synthesiszed. The reaction can be understood by assuming the formation of the hypothetical cyclobutene 159 from 156 [52],... 

---