Montanari

The large sulfur atom is a preferred reaction site in synthetic intermediates to introduce chirality into a carbon compound. Thermal equilibrations of chiral sulfoxides are slow, and parbanions with lithium or sodium as counterions on a chiral carbon atom adjacent to a sulfoxide group maintain their chirality. The benzylic proton of chiral sulfoxides is removed stereoselectively by strong bases. The largest groups prefer the anti conformation, e.g. phenyl and oxygen in the first example, phenyl and rert-butyl in the second. Deprotonation occurs at the methylene group on the least hindered site adjacent to the unshared electron pair of the sulfur atom (R.R. Fraser, 1972 F. Montanari, 1975). 

Both of these structures are open-chained compounds corresponding to crown ethers in function if not exactly in structure (see Chap. 7). They have repeating ethyleneoxy side-chains generally terminated in a methyl group. Montanari and co-workers introduced the polypodes 22 as phase transfer catalysts . These compounds were based on the triazine nucleus as illustrated below. The first octopus molecule (23) was prepared by Vogtle and Weber and is shown below. The implication of the name is that the compound is multiarmed and not specifically that it has eight such side-chains. Related molecules have recently been prepared by Hyatt and the name octopus adopted. For further information on this group of compounds and for examples of structures, refer to the discussion and tables in Chap. 7. 

Pyrimidines have also served as electrophiles in crown synthesis from this group. 4,6-Dichloropyrimidine reacts with diethylene glycol and sodium hydride in anhydrous xylene solution to form the 20-crown-6 derivative as well as the other products shown in Eq. (3.48). Note that a closely related displacement on sy/rr-trichlorotriazine has been reported by Montanari in the formation of polypode molecules (see Eq. 7.5). 

A good deal of work has been done on polymeric crown ethers during the last decade. Hogen Esch and Smid have been major contributors from the point of view of cation binding properties, and Blasius and coworkers have been especially interested in the cation selectivity of such species. Montanari and coworkers have developed a number of polymer-anchored crowns for use as phase transfer catalysts. Manecke and Storck have recently published a review titled Polymeric Catalysts , which may be useful to the reader in gaining additional perspective. 

Montanari and coworkers have been particularly active in this area. They have generally utilized crowns or cryptands having long arms attached to them. These lipophilic arms are typically terminated in a primary or secondary amino function which may serve as a nucleophile in the reaction with a chloromethylated polystyrene residue. 

Montanari and his coworkers used the interesting polypode ligands derived from sym-trichlorotriazine as phase transfer catalysts for a variety of transformations. These catalysts were quite successful and their formation is illustrated below in Eqs. (7.3)— (7.5). Comparisons were also made with certain pentaerythrityl derived polypodes as well. These latter compounds are listed in Table 7.1 as compounds 10—13. 

Although the cryptands are powerful cation complexing agents, there has been a need felt for increasing the lipophilicity of these materials. In particular, Montanari and his coworkers have utilized the lipophilic cryptands in phase transfer catalytic proces-sesi5,40 Lehn and his group. In all of this work, the principal structural varia-... 

Landini, Montanari and Rolla ° were able to incorporate cyclohexyl residues in the strands and thereby increase lipophilicity. As with the compounds referred to above, these were effective phase transfer catalysts. 

W. P. WF-BERandC. W. GOKEL, Phase Transfer Catalysis in Organic Synthesis, Vol. 4 of Reactivity and Structure, Springer-Verlag, 1977, 250 pp. C. M. Starks and C. Uotta, Phase Transfer Catalysis, Academic Press, New York, 1978, 365 pp. F. MontanaRI, D. Landini and F. Rolla, Topics in Current Chemistry 101, 149-201 (1982). E. V. Dehmlow and S. S. Dehmlow, Phase Transfer Catalysis (2nd edn.), VCH Publishers. London 1983, 386 pp. T. G. Southern, Polyhedron 8. 407-13 (1989). 

Montanari, F., Landini, D., and Rolla, F. Phase-Transfer Catalyzed Reactions. 101, 149-200 (1982). 

Phase-transfer catalysed reactions. F. Montanari, D. Landini and F. Roll a, Top. Curr. Chem., 1982, 101,147-200 (295). 

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