Diynes, ring closures with

Chlorotris(triphenylphosphine)rhodium(I) Ring closures with diynes... 

The reaction of Ba[P(SiMe3)2]2(THF)2 with diphenylbutadiyne in toluene for 12 days induces a m-addition of the diyne to the phosphide, followed by a 1,3-silyl group shift and ring closure. The dinuclear complex 132 is then isolated in good yield.283 Its complex structure contains Ba-C a bonds (2.881(5), 2.899(5) A), side-on Ba-alkyne (3.003(6), 3.363(6) A) and arene interactions, and Ba-phospholide bonds (Ba-P = 3.487(2) A) (Figure 65). 

Intramolecular bridging is also observed. For functionalized dienes (e.g., RCH=CHCOCH=CHR), ring closures occur with the formation of thiacyclohexanones, while the related bis alkenylketones result in the formation of the corresponding thiacyc-lohexadienones . Simple thiophene derivatives are formed by insertion of diynes into SCI2 . Similar chemistry is reported for Se halides, and tricyclo thia- and selena ethers are obtained from sequential addition of SCI2 and SeCb to cyclooctatetraene . 

TMS methylpyrazole (279) is formed by the reaction of l,4-bis(TMS)-buta-l,3-diyne (207) with anhydrous hydrazine in abs. ethanol154. The reaction is initiated by a nucleophilic attack of hydrazine at carbon-1 of 207, forming a hydrazone via rearrangement and, after partial desilylation and ring closure, 279 can be isolated (equation 126). 

Electrocycylic ring closure combined with Diels-Alder addition has been employed to derive all four rings of the tetracyclic ring system in the steroids by means of a one pot synthesis (ref.198). Thus, from the triflate of hex-4-ynol and the readily available hexa-1,5-diyne a triyne intermediate was obtained which with chromium or tungsten hexacarbonyl formed a triyne carbene complex. This with a 1,3-dialkoxybuta-1,3-diene in acetonitrile with carbon monoxide 0 atmosphere) initially at ambient temperature and then at 110°C over 24 hours afforded a 62% yield of the two products shown [(1) R = TBS (2) R = H, (1) (2) 5 2]. 

We found that methyl or ethyl substituted diynes give Acyclic Diyne Metathesis Condensation (ADIMET) which is similar to the Acyclic Diene Metathesis (ADMET) of dienes. The catalysts we used for ADIMET reactions are the Schrock type carbyne complex ( BuO)3W=C Bu or W2( BuO)6. For ADIMET reactions we used no or only small amonts of solvent. With higher amounts of solvents Ring Closure Metathesis (RCM) of diynes occured. 

The key step in this sequence is the Cadiot-ChodMewicz coupling between the corresponding terminal diyne l(n) and two equivalents of the THP-protected l-bromoprop-l-yne-3-ol (7). The ring closure to 10(n) was achieved by reacting 9(n) with various primary amines in the presence of K2CO3 as base. The yield was highest (70%) for 10(5)c. 

The above are in class of cascade of reactions, that involve two successive transformations Ru-catalyzed coupling of 1,6-diynes with acyclic alkenes forming bicyclic cyclohexadiene through electrocyclic ring closure and the migration of the double bond. Under the same reaction conditions, the [2-b2-b2] cycloaddition with cyclic olefins results in tricyclic cyclohexadienes with another arrangement of conjugated double bonds. 

In this general area quite efficient intramolecular examples have been described as well (Scheme 6). A thorough examination of the intermediates and likely mechanisms associated with this system has been published. In particular, it has been found that the type of metallacycle formed depends on the length of the chain separating the two alkyne units in the diyne. Efficient intramolecular cycloaddition to a bicy-clic metallacycle occurs only from 1,6- and 1,7-diynes. The poor results on attempted cyclization of 1,5-diynes to give highly strained bicyclo[3.2.0]hepta-l,4-dien-3-ones result from resistance towards closure of the strained four-membered ring upon metallacycle formation. ... 

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