Acetylene ring closure with

Diaroylcyclohexadienes which can be prepared from acyclic dienes and dibenzoyl-acetylene undergo ring closure with p-toluenesulfonic acid in benzene to afford benzo[c Jfurans. 

A new route to ( )-trachelanthamidine (6) and ( )-isoretronecanol (5) has been reported by Nossin and Speckamp.12 Cyclization of the ethoxy-lactam (28), which is formed on reduction of the imide (27), led to ring-closure with the acetylene to give, after hydrolysis, a 4 1 mixture of the epimers (29) and (30) (Scheme 7). The preferential formation of the five-membered ring is considered to be due to stabilization of an exocyclic vinyl cationic intermediate by the phenylthio group. Reduction of the separated diastereoisomers (29) and (30) yielded ( )-trachelanthamidine (6) and ( )-isoretronecanol (5), respectively. 

Derivation (1) Condensing citral with acetone followed by ring closure with an acid, (2) reaction of acetylene with acetone followed by hydrogenation, condensation with diketone, and further reaction with acetylene. 

Mercuric oxide sulfuric acid Ring closure with acetylene derivs. 0-Heterocydics... 

The stereoselective synthesis of y-bisabolenes was made possible by the development of a new method for the carbosilylation and double alkylation of an acetylenic function coupled with ring closure, overall addition of three carbon substituents to two acetylenic carbons. 

A titan acycl open tadi en e generated from an acetylene having an ester group at a suitable position reacts intramolecularly with this functional group, as exemplified by Eq. 9.13. Here, both carbon—titanium bonds of the titanacycle participate in the reaction to effect ring-closure [33]. 

Base-induced isomerization of propargyl amide 29a gives chiral ynamide 30a, which is subjected to ring-closure metathesis to afford cyclic enamide 31a. Diels-Alder reaction of 31a with dimethyl acetylene dicarboxylate (DMAD) gives quinoline derivative 32. In a similar manner, propargyl amide 29b is converted into ynamide 30b, RCM of which gives bicyclic compounds 31b and 31b in a ratio of 1 to 1 (Scheme 10). 

Not only acetylene derivatives do undergo palladium catalysed intarmolecular carbon-nitrogen bond formation with amines. The similar reaction of olefins in a Wacker-type process also leads to ring closure. (0-Aminopentenes bearing a suitable leaving group in the 4-position were converted to pyrroles in a cyclization-isomerisation-elimination sequence (3.65.),82... 

The low reactivity of ethylene can be overcome by using phenyl vinyl sulfone Ph-S02CH=CH2 instead.853 The PhS02 group can be easily removed with Na-Hg after the ring-closure reaction. Similarly, phenyl vinyl sulfoxide PhSOCH=CH2 can be used as a synthon for acetylene.854 In this case PhSOH is lost from the sulfoxide product (7-12). 

The foregoing mechanism for addition of methylene to the double bond is substantiated by the observation of Jacox and Milligan69 that allene but not cyclopropene is produced upon reaction of CH2 with acetylene in an argon matrix at 4°K. It is quite reasonable to expect in this case that the rate of ring closure would be slow compared to the rate of hydrogen migration. 

The synthesis of 2-arylbenzofurans 226 by heterocyclic ring closure of acetylenic compounds 225 with pyridine hydrochloride is a variation487 of the general method of heterocyclic ring closure of acetylenic compounds 221. 

The 1,4-diphospha-l,3-butadienes are suitable as ligands for cr-coordi-nated complexes with transition metals. Attempts to carry out pericy-clic reactions with maleinic anhydride, acetylene dicarboxylate esters, dimethylbutadiene, or cyclopentadiene failed, but Diels-Alder reactions with norbornadienes were successful (94). Earlier attempts to synthesize 1,4-diphosphabuta-l,3-dienes with oxalychloride and phenyl-bis(silyl)phosphane proceeded via ring closure [Eq. (42)] (89), where R = Ph (a) or [Pg.285]

This benzannelation provides the key step in a synthesis of the anthracycline 5. Thus reaction of the complex 2 with the acetylene 3 provides, after oxidation, the tetrahy-dronaphthol 4. The fourth ring of 5 is formed by ring closure to an anthrone followed by air oxidation (Triton B) to an anthraquinone. ... 

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