Monensin, a polyether antibiotic, was isolated from a strain of Streptomyces cinnamonensis in 1967, and its structure was determined shortly thereafter. HO Et Me Me. Me H Me Me OMe Me COOH HO, Me Monensin This molecule exhibits a broad-spectrum anticoccidial activity that, since its introduc- tion in 1971, has been used as a treatment for coccidial infections in poultry and as an additive in cattle feed. In the synthesis of monensin, Y. Kishi chose to create the molecule in sections and then join them to create the target molecule. Following is an outline of the steps by which he created the seven-carbon-chain building block on the left side of the molecule. СООН (3) ОН (4) Me Ме Me H. COOEt (6) (7) HO, Me Ме Me Ме Me ОН OMe OBn (8) OBn (9) OBn (10) Ме Me Me Me Me М OMe OMe H OMe Me HO, (12) (13) Me Me Me Me Me Me ČOOME OMe OMe OH several steps Me (14) Me Me Me Me Me HO OH H 7. O: OMe OH turn in space and compare with monensin TH. Мев MEOOC. OH Ме Me Me Me 3. OMe Ме COOME
Reactive Intermediates
In chemistry, reactive intermediates are termed as short-lived, highly reactive atoms with high energy. They rapidly transform into stable particles during a chemical reaction. In specific cases, by means of matrix isolation and at low-temperature reactive intermediates can be isolated.
Hydride Shift
A hydride shift is a rearrangement of a hydrogen atom in a carbocation that occurs to make the molecule more stable. In organic chemistry, rearrangement of the carbocation is very easily seen. This rearrangement can be because of the movement of a carbocation to attain stability in the compound. Such structural reorganization movement is called a shift within molecules. After the shifting of carbocation over the different carbon then they form structural isomers of the previous existing molecule.
Vinylic Carbocation
A carbocation where the positive charge is on the alkene carbon is known as the vinyl carbocation or vinyl cation. The empirical formula for vinyl cation is C2H3+. In the vinyl carbocation, the positive charge is on the carbon atom with the double bond therefore it is sp hybridized. It is known to be a part of various reactions, for example, electrophilic addition of alkynes and solvolysis as well. It plays the role of a reactive intermediate in these reactions.
Cycloheptatrienyl Cation
It is an aromatic carbocation having a general formula, [C7 H7]+. It is also known as the aromatic tropylium ion. Its name is derived from the molecule tropine, which is a seven membered carbon atom ring. Cycloheptatriene or tropylidene was first synthesized from tropine.
Stability of Vinyl Carbocation
Carbocations are positively charged carbon atoms. It is also known as a carbonium ion.
Propose a reagent or reagents for Steps 1–14. Note that this fragment contains five chiral centers. You do not have to predict or rationalize the stereochemistry of each step, but only propose a reagent or type of reagent to bring about each step.
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