Proton removal rationale

Finally if the steps which lie between chanoclavine-I and proton removal are reversible and if proton abstraction is rate-limiting, the tritium enrichment of unreacted chanoclavine-I, which was observed in the above experiments, is also explained. (Loss of tritium is slower than loss of hydrogen as the result of a primary isotope effect.) So we now have a most satisfying rationale for the steps involved in the formation of the tetracyclic ergot alkaloids from chanoclavine-I. 

A transition state model proposed by Marshall for the rearrangement is shown in Scheme 1. The chiral amide 63 coordinates either one of the two enantiotopic propargylic protons in the chair-like conformation (Scheme 1). Complex I should be of lower energy as it lacks the unfavorable 1,4-phenyl/alkyne interactions present in complex n, thus the pro-S proton was removed predominantly. This rationale suggests that the enantioselec-tivity is predominantly determined at the Uthiation step. 

Reaction of butyllithium with VBE tetrahydroisoquinolyl formamidine proceeds as shown in Scheme 56. The lack of a kinetic isotope effect in deuteriated substrates revealed that the slow step in the sequence is the complexation of the BuLi with the formamidine, followed by selective removal of the a proton as shown. A rationale for this selectivity is that the butyl group is oriented trans to the isopropyl of the 5-membered... 

Since there are six carbon atoms on the left side, one must also have six on the right, and thus x — 6/4 = 3/2. With the same rationale as above, the oxidation state of carbon in fumaric acid is +2/4 = +1/2. Then one needs to remove an equivalent of 1.5 electrons from each carbon in benzene, i.e., 1.5 x 6 = 9 = 2. The charge balance requires 9 protons = y = z, and thus there is a total of y + 3/2(6) =18 hydrogens on the product side, which leads tow = 18/2 = 9. Then,... 

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