 Welcome to this course on Transition Metal Organometallics in Catalysis and Biology. Today we will be talking about Ring Closing E9 Metathesis Reaction or in short it is called RCEYM. Now this discussion on Ring Closing E9 mechanism has been a discussion that has been going on in the past few lectures where we have tried to characterize this particular type of reaction and what we have learned is that this ring closing in E9 metathesis reaction they occur first in high dilution conditions because these are intramolecular reactions whereby under dilute conditions the competing intermolecular reactions like cross metathesis reactions for the alkene and alkyne substrates are suppressed. Also what we have learned in our earlier discussion is the fact that this in mechanism metathesis reaction mechanism proceeds via in first pathway whereby the metathesis occurs on the alkene first then subsequently it moves on to the alkyne. The reason for this is that if the reverse were to take place that if it is where to proceed by alkyne first mechanism then the residual selectivity is lost then what is observed in terms of the with regard to the product formation. So today we are going to take a look at some more examples of Ring Closing in E9 Metathesis reactions or RCEYM Ring Closing Metathesis Reaction. So this is illustrated for the substrate shown given below for the catalyst CH2. Now the reaction would proceed by forming the corresponding metallocyclobutene species as is shown by here. This active species would react with the alkene first in the alkene first pathway giving the metallocyclobutene intermediate as it is shown over here and then that would also undergo rearrangement as it is shown here to give the active species like this. Now that would then react with the alkene in the fashion shown over here to give this intermediate now can then undergo rearrangement as shown here to give and that in presence of another olefin would give the desired compound. So this formation of this is favored so this is another example by which this pathway is favored. There are some possibilities or other possibilities like formation of a semi-membrane as is shown here something like this is not observed. So the favored product is what is shown over here. So we are going to take a look at some more examples of this Ring Closing in E9 mechanism wine metathesis reactions and this we have worked out in some examples and this in short can be represented by a substrate having an alkene as well as an olefin and this in presence of the catalyst which is a metal carbene species. The product is a diene of the type R1 and R2. So this is a conjugated diene of this formula. So in the past few lectures we have taken look at several of these kind of reaction reaction. We are going to take a look at few examples of this type of chemistry as is shown over here. Here is a bifinyl substrate that in presence of a tungsten carbene fissure type of complex the product which formed thus is so this was reported by professor Katz in 1985 and what this reaction shows is the fact that this moiety this conjugated moiety is formed in the product as well and can be seen over here. So this above is a general representation of this Ring Closing E9 metathesis reaction. So we are just going to take a look at a carton mechanism proposed for these kind of substrates which is shown over here this R then R reacts with the metal catalyst. Now there are two possibilities that this can undergo in first mechanism or it can undergo ion first mechanism and there is also a possibility that though possibility that there can be a metallocycle there can be a metallocycle formation mechanism. So there the proof for the support for the infi mechanism was given by Katz in 1985 and the trust proposed this metallocycle mechanism in 1991. However, the most popular mechanism to grain carrier lens is the in first mechanism and that is the one which is now believed to be gaining grounds. So let me just show the mechanism proposed by Katz which is the ion first mechanism and the one that is shown by professor Kross as well so in the ion first mechanism as proposed by the Katz it is supposed to attack the ion first giving the metallocycle butane that further giving then it is attacking the olefin now. So this would result with the product in the trust mechanism what is said is so this is the Katz ion first mechanism which is this and the trust mechanism is this in present of acetate and the metal would give a metallocycle which will undergo reductive elimination release the metal to give this metallocyclobutane compound that would then undergo rearrangement to give the desired product. So this is the trust pathway apart from the in first mechanism which we had discussed earlier. So even though the in first mechanism is by far the most popular one there are possibilities of ion first as is shown over here where alkene getting reacted with the metal catalyst and other is the metallocycle as proposed by trust these two mechanisms have been proposed for this alkene alkene metathesis reaction however they have not met with much success though. So Katz mechanism involves formation of metallocyclobutane intermediate in a in first pathway whereas crossed mechanism involves formation of metallocyclo pentane formation of metallocyclo pentane intermediate and however they are different however the most popular the in first mechanism is by far the most accepted one the in first mechanism by far is the most accepted one for the in ion metathesis reactions. So proceeding further here is a nice example of vinyl cycloalkenes are formed vinyl cycloalkenes formation with high stereoselectivity this is explained for the in the example CO2 et CO2 et so this has a easy ratio 80 to 20 easy ratio in presence of ruthenium catalyst it provides makes the six membered ring with this conjugated olefin in high yields 86% yield and greater than 98% e olefin so this is a highly selective way of synthesizing this vinyl cycloalkene ring using this in ion metathesis reaction. So the major drawback in spite the successful utility of these reactions that we have covered the major drawback of this in ion reaction as discussed earlier is the formation of other metathesis products like the drawbacks and homodimeric products. So pros pros and cons of in ion metathesis the limitation is is cross metathesis reaction reactions so this is the limitation now one thing to note here that the in accordance with in ion metathesis where there is an olefin and alkyne which undergoes metathesis there are also reactions which are in in metathesis and the limitation for this in in mechanism the limitation is homodimeric products is the formation of homodimeric products similarly homodimerization is not an issue for in ion metathesis similarly homodimerization is not a problem for in ion metathesis and one major important feature about metathesis reaction is they provide viable alternative to many other reactions like wittig reactions or McMurray synthesis metathesis reactions provide alternatives to classical wittig reaction and copper catalyzed alkyne coupling and McMurray synthesis. So with this we come to the end of today's discussion on ring closing in ion metathesis reaction what we have observed in today's class is that we have looked at various mechanistic pathways which has been proposed for explaining in ion metathesis reaction to begin with we had already in earlier class looked at in first mechanism pathway in which the alkene is undergoes metathesis first and in today's lecture we have looked at two other proposed common pathway one is the ion first pathway proposed by cats in which the metathesis of the alkene is first proposed though we had already discussed that this suffers from limitation because of loss of stereo regio selectivity because of isomerization process that may happen and beyond cat's pathway the another proposed pathway had been by trust in which five membered metallacyclo pentane pentene has been proposed but these two mechanism has not found ground in compare in presence of the in first mechanism which we have discussed in detail. We have also looked into the variety of in ion metathesis in terms of we have looked to a new form called in in metathesis and what we had seen that cross metathesis is a problem for E9 and homodimerization is a problem for in in metathesis however for E9 metathesis homodimerization does not play a much important role at lastly to summarize this metathesis reaction what we had noted is that metathesis reaction provide a nice alternative to many classical reactions in organic chemistry like Wittig coupling or copper characterized alkene coupling or McMore synthesis so with this we come to an end of today's class I once again thank you for being with me in this lecture and I look forward to discussing this in ion metathesis in bit more detail when we meet in the next class till then goodbye and thank you.