Cyclopropenyl cation synthesis

Alkylation of enamines with epoxides or acetoxybromoalkanes provided intermediates for cyclic enol ethers (668) and branched chain sugars were obtained by enamine alkylation (669). Sodium enolates of vinylogous amides underwent carbon and nitrogen methylation (570), while vicinal endiamines formed bis-quaternary amonium salts (647). Reactions of enamines with a cyclopropenyl cation gave alkylated imonium products (57/), and 2-benzylidene-3-methylbenzothiazoline was shown to undergo enamine alkylation and acylation (572). A cyclic enamine was alkylated with methylbromoacetate and the product reduced with sodium borohydride to the key intermediate in a synthesis of the quebrachamine skeleton (57i). 

The structurally characterized derivative of the diphosphirenium cation 12 is a known species [112-116], The gas-phase synthesis and pentaquadrupole MS characterization, and CID (with argon) of the first azaphosphirenium cation 13 (the N,P analogue of the cyclopropenyl cation) were also reported recently [117] (Scheme 14). Although this compound has not been characterized structurally, the similarity of the B3LYP/6-311++G calculated PC and CN(exocyclic) bond lengths of 13 to... 

The synthesis and properties of the parent cyclopropenyl cation itself were reported in 1967 ". A major hurdle in the synthesis of this species involved the preparation of the precursor 3-chlorocyclopropene (20). Under appropriate conditions this compound can... 

Preparation of Aromatic Compounds via Dehydrogenation. Dihydroaromatic compounds are easily converted into the corresponding aromatic compound by treatment with triphenylcarbenium tetrafluoroborate followed by base. Certain a,a-disubstituted dihydroaromatics are converted to the 1,4-dialkylaromatic compounds with rearrangement (eq 1). Nonbenzenoid aromatic systems, e.g. benzazulene or dibenzosesquifulvalene, are readily prepared from their dihydro counterparts. Aromatic cations are also easily prepared by hydride abstraction, for example, tropylium ion (e.g. in the synthesis of heptalene (eq 2)), cyclopropenyl cation, and others, including heterocycUc systems. Some benzylic cations, especially ferrocenyl cations, can also be formed by either hydride abstraction or trityl addition. 

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