Dienyne derivatives

Synthesis of a polyoxygenated bicyclic compound containing a medium-sized ring is achieved via tandem metathesis of the dienyne derived from D-ribose (Equation (11)). ... 

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],... 

Lewis-acid catalysis is effective in intermolecular as well as intramolecular /zomo-Diels-Alder reactions. Thus, complex polycyclic compounds 93 have been obtained in good yield by the cycloaddition of norbornadiene-derived dienynes 92 by using cobalt catalyst, whereas no reaction occurred under thermal conditions [91] (Scheme 3.18). 

The intramolecular approach of Staab and Graf, shown in Scheme 4, precluded formation of 5, but was considerably more involved [12]. The cyclic dienyne 6 was afforded by Wittig reaction of o-phthaldialdehyde with the corresponding bis(ylide) derived from tolane. Bromination of 6 and subsequent treat-... 

Numerous studies aimed at the understanding of the mechanism of these processes rapidly appeared. In this context, Murai examined the behavior of acyclic linear dienyne systems in order to trap any carbenoid intermediate by a pendant olefin (Scheme 82).302 A remarkable tetracyclic assembly took place and gave the unprecedented tetracyclo[6.4.0.0]-undecane derivatives as single diastereomer, such as 321 in Scheme 82. This transformation proved to be relatively general as shown by the variation of the starting materials. The reaction can be catalyzed by different organometallic complexes of the group 8-10 elements (ruthenium, rhodium, iridium, and platinum). Formally, this reaction involves two cyclopropanations as if both carbon atoms of the alkyne moiety have acted as carbenes, which results in the formation of four carbon-carbon bonds. 

To complete the range of geometric isomers of terminal and non-terminal dienes and trienes available, systems nominally derived from inaccessible (Z)-alkenylzirconocenes are desirable. Fortunately, insertion of the various carbenoids discussed above into mono- or bis(alkynyl) zirconocenes 64 and 65 affords dienyne products 66 [38], which are readily reduced to the desired ( ,Z,2)-trienes (Scheme 3.15) [45—47]. Insertion of the f5-alkynyl carbenoid 62 allows a convenient access to (Z)-enediynes 67. 

Benzannulation reactions of Fischer carbene complexes have proved a useful route for the synthesis of benzene rings fused to one furan ring and one additional heteroaromatic ring (Equation 96) <2005TL2211>. Thus, reaction of chromium carbene complex 168 with the conjugated dienyne systems produces benzofuran derivatives (Table 7). 

The most thorough analysis of the relative contributions of the three competing pathways (see Scheme 3) is due to Zimmermann and co-workers, who have addressed this problem by studying the thermocyclization of various substituted and D-labeled dienynes, in which, inter alia, one of the double bonds was part of a benzene ring. As summarized in Scheme 8 for the two acetylenes 27 and 30, which cycloaromatize to naphthalene (31) and its two mono-deuterio derivatives 28 and 29 on flash vacuum pyrolysis, the radical route (pathway (c)) plays a significant role in the formation of all these aromatization products [9, 16]. 

Chiral dioxabicyclic systems are selectively formed from 3,4-bisallyloxybut-1-yne derivatives under an ethylene atmosphere. A single RCM is performed when a RuCl2(PCy3)2(= CHPh) is employed, while the cascade RCM of dienyne is the major reaction with a second generation Grubbs catalyst (Scheme 5). In this case, the substitution of the allyloxy groups can selectively lead to dioxabicyclo[4.4.0]decane or to dioxabicyclo[5.3.0]decane [13]. 

A catalytic tandem cyclopropanation-ring-closing metathesis of dienyne 80 led to derivative 81 in good yield (Scheme 30 <2004JA9524>). For internal alkynes, carbene-mediated ring-closing enyne metathesis was observed. Less favorable alkyne binding leads to preferential reactions of the metal carbene with the 1-alkene moiety. 

The dienynes (34) derived from cyclic ketones also undergo cyclization to accomplish a cyclopent-enone annulation. " Scheme 23 contains representative structures. The cyclododecyl system was derived from a silyldienyne prepared by a novel condensation route shown in equation (27). ... 

Further examples of the applications of thiophosphates in organic synthesis have been reported. The methodology based on intermediate thiophosphates (138) constitutes a general and convenient route to a wide range of conjugated non-linear trienynes (139). Thiophosphate (138) reacts readily with sodium derivative of dienynes to form (139) in one operation via single and double carbon-carbon bond formation (Scheme 41). ... 

Irradiation of the dienyne (185) results in hydrogen abstraction from solvent affording the triene (186). In contrast the irradiation of enyne (187) results in bond fission and isomerization yielding the cyclohexene derivative... 

The synthesis of bis-aryloxo titanacyclopent-2-ene and titanacyclohept-3-ene (Scheme 93) derivatives has been reported via tricyclization of dienynes. The molecular structure of the titanacyclohept-3-ene has been determined by X-ray diffraction. It is suggested that the formation of the titanacyclohept-3-ene compound proceeds through an insertion of olefin into the Ti-vinyl bond of a titanacyclopent-2-ene intermediate. The metallacycles show interesting reactivity and synthetic usefulness and form novel organic molecules by hydrolysis and thermal catalysis.178... 

Lewis acid catalyzed versions of [4 4- 2] cycloadditions are restricted to functionalized dieno-philes. Nonfunetionalized alkenes and alkynes cannot be activated with Lewis acids and in thermal [4 + 2] cycloadditions these suhstrates usually show low reactivity. It has been reported that intcrmolecular cycloaddition of unactivated alkynes to dienes can be accelerated with low-va-lent titanium, iron or rhodium catalysts via metal-mediated - -complex formation and subsequent reductive elimination39 44. Usually, however, low product selectivities are observed due to side reactions, such as aromatization, isomerization or oligomerization. More effective are nickel-catalyzed intramolecular [4 4- 2]-dienyne cycloadditions which were developed for the synthesis of polycycles containing 1.4-cyclohexadienes45. Thus, treatment of dienyne 1, derived from sorbic acid, with 10mol% of Ni(cod)2 and 30 mol % of tris(o-biphenyl) phosphite in tetrahydrofuran at room temperature affords bicyclic 1,4-dienes 2, via intramolecular [4 + 2] cycloaddition, with excellent yield and moderate to complete diastereocontrol by substituents attached to the substrate. The reaction is sensitive towards variation in the catalyst and the ligand. 

CycUzations. In a catalytic process 2-aryl-3-alkenylindoles are generated from aldimines derived from o-alkynylanilines. Cyclization reactions of enynes and dienynes under reductive conditions (HCOOH)" or in the presence of aryl iodides to participate in a coupling process are useful. 

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