Ring exchange reactions

A more highly substituted pyrrolidone, doxapram, shows activity as a respiratory stimulant. Preparation of this agent involves an interesting rearrangement, which in effect results in a ring exchange reaction. Alkylation of the anion from diphenylacetonitrile with the chloropyrrolidine 14 affords 15. Hydrolysis of the nitrile function leads to the... 

The furan transfer reaction was extended to the furan-pyrrole ring exchange reaction by using propargylamines [138],... 

The first study of ring-exchange reactions involving metallocenes has shown that vanadocene is quite inert to exchange with both Li(C5D5) and Ni(jt- 503)2. ... 

Interesting new developments in chromium chemistry which have been reported this year include the preparation of butadienetetracarbonylchromiurn by treating chromium atoms with butadiene, followed by subsequent treatment with The first ring-exchange reactions involving metallocenes have... 

The energetics of the Cp ring exchange reaction between calcium and lithium have been examined using B3PW91/LANL2DZ calculations. For the reaction... 

Radiolabeled folate provides a powerful tool for folate bioavaHabiUty studies in animals and for diagnostic procedures in humans. Deuteration at the 3- and 5-positions of the central benzene ring of foHc acid (31) was accompHshed by catalytic debromination (47,48) or acid-cataly2ed exchange reaction (49). Alternatively, deuterium-labeled fohc acid (32) was prepared by condensing pteroic acid with commercially available labeled glutamic acid (50). 

The side chain in spirostan derivatives (44) can undergo certain exchange reactions which are characteristic for this skeleton. In general, this spiro-ketal moiety is quite stable under alkaline or neutral conditions, but in acidic media it undergoes a reversible opening of ring F (45 and 46). In... 

The Cornforth rearrangement involves the thermal interconversion of 4-carbonyl substituted oxazoles, with exchange between the C-C-O side-chain and the C-C-O fragment of the oxazole ring. These reactions generally involve compounds where a heteroatom (-OR, -SR, -Cl) is attached to the 5-position (R2) of the starting oxazole. 

Scheme 8-15 Ring opening reaction via hydrozirconation/exchanges reactions (n = 1,2)...

The reaction in Entry 8 was conducted in excess refluxing vinyl f-butyl ether, using 1.1 equivalent of Hg(OAc)2 to catalyze the exchange reaction. In Entry 9 a thermal reaction leads to formation of an eight-membered ring. 

The electron-rich and cyclically conjugated 8 rr electron system of 1,4-dihydropyrazine can be stabilized in essentially planar conformation by organosilicon substitution at the enamine nitrogen centers [1], In addition to electron transfer [1] and triorganosilyl exchange reactions [2], we have explored the possibility of inserting heterocumulenes X=C = Y into one or both of the N-Si bonds of the compounds 1 in order to functionalize this unusual ring structure [3],... 

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