Heterocycle Intermediates

In contrast to the ben2enoid intermediates, it is unusual to find a heterocyclic intermediate that is synthesized via the parent heterocycle. They are synthesized from acycHc precursors. 

A zwitterionic, heterocyclic intermediate was found in the dimerization of propanethial 5-oxide (80JA2490). 

We have investigated the reaction of NH phosphinous amides with diphenyl-cyclopropanone. The products were unequivocally identified as the corresponding p-phosphinyl carboxamides 27 resulting from the hydrolysis of a presumed heterocyclic intermediate (Scheme 28) These results await publication. 

Another approach to the rapid synthesis of complex polycycles from simple acyclic compounds is via the Ni(COD)2-catalyzed reaction of an enone containing an alkyne moiety to give a carbo- or heterocyclic intermediate, which is quenched with an electrophile. A typical transformation as shown by Montgomery and his group... 

This procedure is satisfactory for the synthesis of a variety of aryl sulfonamides. The heterocyclic intermediate used in the synthesis of chlorsulfuron is prepared according to K. R. Hoffmann and F. C. Schaeffer (Ref. 5) as shown in Figure 5. 

The step 3 was reacted with IV-chlorosuccinimide and the heterocyclic intermediate isolated in 82% yield. 

Chemistry of Aromatic lleterocycles. In contrast to the benzenoid intermediates, ii is unusual lo find a heterocyclic intermediate that... 

The reductive silylation under these conditions renders possible an access to useful heterocyclic intermediates which undergo various electrophilic displacements (Scheme 21)105 of the TMS moiety. In the first step phenazine (149) is converted to the corresponding 5,10-bis(TMS)-5,10-dihydrophenazine (150) that can be acylated in excellent yields to the desired 5,10-diacetyl-5,10-dihydro-phenazine (151). 

The list of economically attractive reactive heterocyclic intermediates also includes dichloroquinoxalines 9 and dichlorophthalazines 10. Anchor systems in both cases are bound to the chromophore via a carbonylamino group, and the reactivities correspond roughly to those of dichlorotriazinyl dyes. 

In this strategy, the heterocycle is of no interest by itself. It merely serves as a vehicle to construct an acyclic molecule with the proper structure and proper configuration. It makes use of the obvious fact, that an heterocyclic intermediate is necessaryly more rigid than its openchain analog so that a higher degree of asymmetric induction is to be expected. 

Zhao [4] prepared pro-catalysts, (VI) and (VII), consisting of a transition metal and two nitrogen donor atoms forming five-membered heterocyclic intermediates. When the pro-catalysts were activated with trimethylaluminium, they were used to prepare ethylene dimers and oligomers. 

By analogy to the halolactonization reaction, the synthesis of cyclic iodocarbonates has been studied with the aim of functionalizing a double bond under regio- and stereocontrol, starting from allylic or homoallylic alcohols. These heterocyclic intermediates are employed for the synthesis of epoxy alcohols, diols and triols. 

Stereocontrolled cyclofunctionalizations of double bonds via heterocyclic intermediates 90T3321. 

The concentrations of partially oxygenated molecular products, particularly carbonyls and peroxides, increased with temperature through the slow combustion region. O-heterocyclic intermediates, such as methyl substituted tetrahydrofurans and oxirans, became particularly prominent. Most oxygenates ceased to be formed in substantial amounts above a... 

Heterocyclic intermediates are being used more and more in synthesis as protecting groups, readily generated and, when their job is done, readily removed. We have seen two examples of this the temporary incorporation of the carboxyl group into a 2-oxazoline ring (Sec. 26.6), and the temporary formation of tetrahydropyranyl (THP) esters, resistant toward alkali but extremely easily cleaved by acid (Problem 16, p. 692). 

The enantioseiective total synthesis of antheridic acid involves the key O-heterocyclic intermediate 375 produced by an intramolecular addition... 

Heterocyclic intermediates in asymmetric syntheses of peptides from a-amino acids 02SL1388. 

Schollkopf, U., Busse, U., Lonsky, R., and Hinrichs, R., Asymmetric syntheses via heterocyclic intermediates. Part 31. Asymmetric synthesis of various non-proteinogenic amino acid methyl esters (functionalized in the carbon chain) and amino acids by the bislactim ether method, Liebigs Ann. Chem., 2150, 1986. 

Schollkopf, U., Pettig, D., Busse, U., Egert, E., and Dyrbusch, M., Asymmetric synthesis via heterocyclic intermediates. Part 30. Asymmetric synthesis of glutamic acids and derivatives thereof by the bislactim-ether method. Michael-addition of methyl 2-alkenoates to the hthiated bislactim-ether of cyclo-(L-Val-Gly), Synthesis, 737, 1986. 

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