A Critical Review of the 2001 Literature Preceded by Two by Gordon W. Gribble and Thomas L. Gilchrist (Eds.)

By Gordon W. Gribble and Thomas L. Gilchrist (Eds.)

This quantity of growth in Heterocyclic Chemistry (PHC) is the fourteenth annual overview of the literature, masking the paintings released on very important heterocyclic ring structures in the course of 2001. during this quantity there are really good studies. the 1st, by way of Jan Bergman and Tomasz Janosik, covers their paintings on sulfur-containing indoles. the second one, by means of David Knight, discusses five- endo -trig iodocyclisations. the next chapters, prepared through expanding heterocycle ring measurement, assessment contemporary advances within the box of heterocyclic chemistry with emphasis on synthesis and reactions.

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_ R OH 2 NHTS 171 R 1, R 2 = alkyl, Ph 12, K2CO 3 MeCN, 0-20~ 172 R1 12, MeCN Ts , I ',R 2 173 R1 Ts R2 174 _I This encouraged us to carry out the cyclizations in the absence of base which provided a significant bonus in that now only the 2,5-cis isomers 174 were obtained. Subsequent experiments confirmed that the trans-isomers 173 were the initially formed, kinetic products which could then undergo acid-catalysed isomerization to the more thermodynamically stable 2,5-eis-isomers 174, either by separate treatment with hydrogen iodide or by exposure to the latter when generated during cyclization in the absence of a base.

The combined organic solutions are washed with water and brine then dried and evaporated. In the examples 27-31, the resulting residue is usually essentially pure iodotetrahydrofuran. Purified by silica gel chromatography and 1020% ether in pentane, the iodotetrahydrofurans are somewhat light-sensitive and are best stored below 0~ in the dark. Et~'"Bu ~ ' Et 28 27 R 29; R = H; CH2CO2Et I MeO2C "Bu 31 "Bu MeO2C 30 I --- S 32 [R = Ph(CH2)2] L I + J 33 "R 34 As can be seen from the variety of model structures 27-31, which were all obtained in >80% isolated yields, both secondary [27] and tertiary [28] alcohols work well and 23 Electrophile-induced 5-Endo Cyclizations cyclizations can be effected onto alkenes with one [27, 28] or two [29] distal substituents, c~Hydroxy-esters also work well [30], not surprising in view of the initial observation by Bartlett and Myerson <78JA3950> as well as [3-hydroxy-esters [11, 31] which gave marginally higher yields (ca.

133 134 R Ph R 1 - - X / - - - ~ ph OR [R1 = CH2OR 2] Ph 136 ~ R I " ~ ' ~ ' O / ~ Ph 135 137 ~ R Et3 Ph H 138 ,SePh 139 ----- ~ R SiEt3 O H~H~,~ph 140 A definitive study of selenocyclizations of alkyl-substituted homoallylic alcohols was reported by Mihelich and Hite <92JA7318>. Employing N-(phenylseleno)phthalimide (NPSP) and p-toluenesulfonic acid as activator in dichloromethane at ambient temperature, both "syn"-(Z)-[95; E = H) and 'anti"-(Z)-[98; E - H] alkenols were found to give essentially single products [142; E = H] and [144; E = H] respectively in excellent yields.

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