Hexa-2,4-diyne, reaction with

Phosgene reacts, sometimes violently, with a large number of common inorganic (Chapter 9) and organic (Chapter 10) substances. Hazardous reactions with lithium, sodium, potassium, aluminium, lithium amide, hexa-2,4-diyn-l, 6-diol, propan-2-ol, and hexafluoropropene have been mentioned specifically [1787]. Mixtures of potassium and phosgene are reported to explode when subjected to shock [1913a]. In addition, phosgene... 

The high reactivity of both intermediates is demonstrated hy their reactions with di- and polyynes from which different products can he isolated depending on the irradiation time. For example, photolysis of 32 in the presence of hexa-1,3-diyne furnishes the bicyclic compounds 35 and 36, which are presumably formed through [2+1] and [2+2] cycloadditions of 33 and 34 to the triple bonds of the diyne. ... 

Cyclization.—Earlier work on the cobalt-catalysed synthesis of the strained 4,5-bistrimethylsilylbenzocyclobutene (29), an o-xylene synthon, has been extended to the synthesis of naphthalenes and polycyclic systems. The basis of the reaction involves the (7 -C5H5)Co(CO)2 catalysed cyclodimerization of bistrimethylsily-lacetylene (BTMSA) with 3-substituted hexa-l,5-diynes to give benzocyclobutenes (29) as intermediates. With 3-alkoxy derivatives (29 R = OMe or OSiMea), further reaction with BTMSA produces the naphthalene (30 = SiMe3), which... 

The reaction of diacetylene and its asymmetric homologs (penta-l,3-diyne, hexa-1,3-diyne) with semicarbazide (72ZOR2605) affords the amides of 3-methyl-pyrazole- 1-carboxylic acid (27) (80°C, EtONa, EtOH, 40 h). Amide 26 undergoes irreversible rearrangement to amide 27 at 80°C (EtONa, EtOH). 

The reaction of hexa-2,4-diyn-l-al (64) with mercaptoacetaldehyde leads to 2-formyl-5-(prop-l-ynyl)thiophene (65). The addition direction is governed by the aldehyde group via intramolecular aldol condensation in the intermediate (77HOU947). 

The thermal solid-to-solid cyclization reaction of diallene derivatives also proceeds stereospecifically. Reaction of 1,6-diphenyl-1,6-di(p-tolyl)hexa-2,4-diyne-l,6-diol (113) with HBr gave meso- (114) and rac-3,4-dibromo-l,6-di-... 

Parker, Raphael, and Wilkinson have investigated a synthetic approach to tropinone (124), which they call the acetylenic route (78). Reaction of hexa-1,5-diyne-l,6-dicarboxylate (145) with methylamine yields the pyrrolidine derivative (146), which by catalytic hydrogenation affords the diester 147 (79,50). 

An example illustrating the synthesis of condensed oxepins by the cobalt-catalyzed reaction of bistrimethylsilylacetylene with a hexa-l,5-diyne derivative is shown in Scheme 175.234 This type of process has been discussed earlier in the context of pyran synthesis (see Scheme 158 in Section V,B,2). 

Fig. 16 (a) Comparison of potential energy profile for the formal Cope rearrangement of 3,4-difluorohexa-l,5-diyne-3-ene with that of (Z)-hexa-l,5-diyne-3-ene, (b) Rehybridization in the C(F) bond along the reaction path. EDI = 3,4-difluoro-hex- 3-ene-l,5-diyne ED2 = 1,6-di-fluoro-hex-3-ene-l,5-diyne BZY = difluoro-l,4-didehydrobenzezne TSBC = the transition state for the Bergman cyclization TSRBC = the transition state for the retro Bergman cyclization. 

Reactions of PhC=CC=CPh with iron carbonyls [Fe(CO)s, Fe2(CO)9, or Fe3(CO)i2] give isomers of complexes Fe(CO)4 (diyne)2 (265), Fe2(CO)6 (diyne)2 (266), and Fe2(CO)7 (diyne)2 (267), to which structures analogous to those found for similar products obtained from C2Ph2 were ascribed all three isomers of the second complex were formed. The reactions of hexa-2,4-diyne and Fe(CO)s have been described in more detail. UV irradiation of mixtures of the two... 

The conversion of an ene-diyne 2.77 into a 1,4-benzenediyl diradical 2.78 on heating is known as the Bergmann reaction . The 1,4-aromatic radical 2.78 maybe converted into benzene or may react with CCI4 to givep-dichlorobenzene (2.79). Bergmann etal converted deuterium-labelled hexa-3-ene-l,5-diyne 2.80 on heating at 200°C into deuterium-labelled hexa-3-ene-l,5-diyne 2.81 in which both deuterium atoms were shifted from the terminal acylene positions to vinyl positions at the interior of the chain. 

The Ni-catalyzed cross-coupling reaction of alkynyl Grignard reagents 60 with ( )- or (Z)-dichloroethene 61a,b has been applied to a simple procedure for the preparation of the protected fomi 62a,b of a highly unstable synthon, as hexa-3-ene-l,5-diyne [Eq. (23). Separation of the diastereomers 62a and 62b is facile since the former is an oil and the latter is a solid [35]. 

Reactions of benzene solutions of arylalkynes with 1 equiv. of chloroacetone and 2 equiv. of Et.iN, using a mixture of (PPhsjaPd and Cul as a catalyst, afford 1,4-diarylbutadiynes in very good yields. Under similar reaction conditions aliphatic 1-alkynes yield a mixture of symmetrically disubstituted 1,4-dialkynyl-l,3-butadiynes and 3-alkyl-4(l-alkynyl)-hexa-l,5-diyn-3-enes (10 equations 15 and 16). 7 This method may represent a good alternative, in nonpolar organic solution, to the Glaser reaction. 

These dimerisation reactions of terminal alkynes have been further extended to the catalytic cyclisation of a,co-diynes. For example, treatment of 1,15-hexa-decadiyne with 10 mol% of 7a affords the endo-msLCTOcydic product, (Z)-l-cyclohexadecen-3-yne with complete stereoselectivity (Equation 5). This novel cyclisation is of particular utility, because synthetic routes to endo-cyc ic (Z)-l-en-3-ynes are extremely limited. A related palladium-catalysed cyclisation of a,co-diynes to give the corresponding exo-cyc c l-en-3-ynes has been reported by Trost and co-workers. 

Fused stiboles (123 R = Me) have also been prepared by this chemistry (Scheme 26). However, on attempted preparation of the bismole (113), the tetraene (51) is the major product. Bismole (113) is only observed by H NMR <93ACS(47)326>. There is a thermodynamic preference for formation of the tetraene since the bismole (113) is stable when prepared from the dianion and PhBiX2. Reaction of the zirconacycle (122 R = TMS) with either PhSbCl2 or PhBiCl2 provides neither heterole (113 R = TMS), (123 R = TMS), nor the tetraene, but instead gives the zirconacycle precursor 1,6-bis(trimethylsilyl)hexa-l, 5-diyne. 

Almost simultaneously, Schroth reported that diacetylene reacts with a hydrazine hydrate solution at 80°C for 4 h to form methylpyrazoles (13) in 80% yield (69ZC108 69ZC110). In the same year, other data concerning the reaction of hydrazine with diacetylene (65°C, EtOH, yield 65%), hexa-2,4-diyne, and 1,4-diphenylbuta-l,3-diyne wCTereported(69JOC999). Later, BASF (93GEP4137011) proposed to carry out the process at 100°C in a polar solvent with a diacetylene concentration of 14-18% in an inert gas. The yield of methypyrazoles was 90% (post-rectification purity 99%). 

Cycloadditions to cage compounds have been reported to give structures containing cyclobutene units. An interesting one-step synthesis of benzocyclobutenes involves the reaction of hexa-l,5-diyne with monoacetylenes, catalysed by cyclo-pentadienylcobalt dicarbonyl. 

The versatile benzocyclobutene synthesis using the dicarbonyl-r) -cyclopenta-dienylcobalt-catalysed acetylene cyclizations has also been applied in a synthesis of (170). Reaction of the acetylene (171) with hexa-l,5-diyne gave the substituted benzocyclobutene (172) which was converted into (170). Use of bistrimethylsilyl-acetylene in the cyclization gave the benzocyclobutene (173). The trimethylsilyl groups are replaceable by electrophiles, and do not impair the ability of the benzocyclobutene to function as an o-xylylene synthon. Reaction of (173) with maleic anhydride gave the adduct (174) quantitatively. 

Other Acetylene Reactions of Mechanistic Interest.—Several recent papers have been concerned with thermal rearrangements of acetylenes. c/ -Hexa-1,5-diyn-3-ene (187) on gas-phase pyrolysis in a flow system at 300 °C undergoes a de nerate thermal rearrangement. Thus pyrolysis of the dideuteriated analogue (188) results in scrambling of the deuterium between acetylenic and... 

Reaction of hexa-2,4-diyne with Fe(CO)6 yields the cyclopentadienone complex (108), characterized crystallographically. Reaction of Fe(CNBu )6 with PhC=CPh yields (109), characterized crystallographically. The ion HFe(CO)4 reacts with acetylenes HC=CCOR to yield products of structure (110), although a crystal structure determination indicates some contribution from a -olefin- -acyl structure. Protonation of (110) yields Fe[t -HRC=C(H)(COR)](CO)4 via an intramolecular decarbonylation. - Photochemical reaction between... 

Simple thermal substitution of CO in the reaetion of Ru3(CO)i2 with hexa-2,4-diyne-l,6-diol leads to Ru3(CO)9(jU-CO) (HO)CH2C=CC=CCH2(OH) with a parallel alkyne. The acetylide complexes (/i-H)Ru3(GO)9 C=CCR(OH)R (R = Me, R = Me, Ph) and their dppm (dppm = bis(diphenylphosphino)-methane) derivatives are also obtained (in four optical isomers) via thermal substitution H and C NMR fluxion-ality and hydration-dehydration reactions have been studied. Dehydration leads to the vinylacetylene derivatives (/i-H)Ru3(CO)7(dppm)(C CC=CH2Ph), formed by loss of the OH group and of one hydrogen of the methyl substituent on the same carbon atom. ... 

On the other hand, hexa-2,4-diyne failed to react, suggesting that 1,3-diynes with the 1- and 4-carbons, connected to sp carbons, are suitable substrates for the present silole-forming reaction. 

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