George W. Gokel

Sulfur heterocycles. I. Use of 4,4-dimethyl-1,3-oxathiolane-3,3-dioxide as a carbonyl anion equivalent

Abstract The title heterocycle is used as a carbonyl anion equivalent in the preparation of aldehydes and α-silyl ketones; the key step is the thermal demasking of the heterocycle by loss of isobutylene and sulfur dioxide.

Macrocyclic polyethers as probes into pheromone receptor mechanisms of a sciarid fly Lycoriella mali Fitch

A series of experiments was undertaken in an effort to understand the possible role of chemical shape and, in particular, the steroid shape in the sex pheromone system of the sciarid fly,Lycoriella mali Fitch. A broad spectrum of compounds includingn-alkanes and macrocyclic polyethers (crown ethers) were tested on sciarid males which were significantly attracted to several test compounds, includingn-heptadecane (the natural pheromone), cycloheptadecane, and a newly synthesized 17-crown-5 isomer which apparently can adopt the steroid shape. The apparent relationship of shape to activity suggests that the steroid template may indeed be of some consequence in insect olfaction.

Synthesis of Ethers

One of the most useful applications of phase transfer catalysis in nucleophilic substitution has been in the Williamson ether synthesis. The reaction of an alkoxide anion with an alkyl halide or sulfonate to give either symmetrical or unsymmetrical ethers (depending on reactants) shows significant improvement in convenience, reaction rate, and yield when conducted under phase transfer catalytic conditions.

The Reaction of Dichlorocarbene With Olefins

Although phase transfer catalysis is a many faceted technique, it was the observation that dichlorocarbene could be generated in a two-phase aqueous-organic system in which sodium hydroxide was used as base that first captured the attention of the organic chemical community. Both Starks [1, 2] and Makosza [3] reported the dichlorocyclopropanation of cyclohexene in the late 1960’s. The reaction was conducted as shown in equation 2.1.

Sulfur heterocycles. II. The hydroxyoxathiolane to acyloin rearrangement

Abstract Thermal control of demasking conditions may be used to convert hydroxyoxathiolanes into either α-hydroxyaldehydes or the corresponding ring-expanded acyloins.

Reactions of Dichlorocarbene With Non-Olefinic Substrates

The reactions of dichlorocarbene with a variety of olefinic and acetylenic substrates have been discussed in Chap. 2. We wish now to turn our attention to the reactions of this species with a number of other substrates which either are non-olefinic or contain double bonds which do not constitute the major reactive function. The substrates considered here are alcohols, imines, amines, amides, thioethers, and hydrocarbons. With the exception of the latter, all of these species appear to react by initial coordination of the electrophilic carbene with a Lewis basic site. Subsequent reactions attributable to differences in the basic function or involvement with other reactive sites lead to differences in the chemistry of each substrate, and each is therefore considered separately.

Reactions of Superoxide Ions

Superoxide salts like potassium and sodium superoxide are virtually insoluble in non-polar media, and although they are somewhat more soluble in hydroxylic media, they are not stable in these solvents [1]. Potassium superoxide is only sparingly soluble in the dipolar aprotic solvent DMSO [2]. As a result of these solubility problems and the inaccessibility of electrochemically generated superoxide [3] in most laboratories, the chemistry of this potentially interesting nucleophile was little studied until recently.

Introduction and Principles

With the probable exception of Wohler’s isomerization of ammonium isocyanate to urea, most of the major advances in organic chemistry have been preceded and presaged by a number of diverse and perhaps minor advances. In some cases the early work was recognized, extended and built upon. In other cases, early examples of particular phenomena were recognized only after a general statement of principles had been offered. Phase transfer catalysis (ptc) is a major advance which is preceded by earlier examples of related phenomena but most if not all of these examples were recognized as examples of phase transfer catalysis only after the principles had coalesced in several minds across the world.

Dibromocarbene and Other Carbenes

The success of phase transfer cyclopropanations with dichlorocarbene naturally stimulated a search for related examples. Numerous trihalomethanes besides chloroform were subjected to phase transfer conditions in the expectation that a wide variety of dihalocyclopropanes would result. Notable among these attempts is the phase transfer generation of dibromocarbene which is discussed in Sects. 4.2–4.5. In addition to the miscellany of dihalocarbenes, the principal successes have been in the formation of sulfur containing (Sect. 4.6) and unsaturated carbenes (Sect. 4.7).

Reactions of Cyanide Ion

Phase transfer catalysis found one of its earliest applications in cyanide displacement reactions. Starks studied this reaction in some detail and it was due in large part to his work that the concepts of phase transfer were so clearly understood at an early stage [1, 2]. There was, of course, other early interest in cyanide ion and these efforts should not be overlooked. Brandstrom had solubilized cyanide ion by his ion pair extraction technique [3]; Solodar had facilitated the benzoin condensation by utilizing tetrabutylammonium cyanide [4]; and Durst [5] and Liotta [6] both used crown ethers to phase transfer cyanide ion. A good deal of other work has now been carried out on phase transferred cyanide ion and is the subject of this chapter.