Olefins continued

Results obtained in glass apparatus are summarized in Figure 1. The unsaturation falls off nearly linearly after a short induction period. After the hydroperoxide functional groups attain their maximum, the olefin disappearance decreases and becomes nonlinear as it is consumed by reaction to form polymeric dialkyl peroxide functions. The maximum concentration of polymeric dialkyl peroxide occurs well after the maximum alkenyl hydroperoxide concentration, giving the appearance of a sequential oxidation mechanism. Infrared and gas-liquid chromatographic analyses showed that hydroxylic derivatives, carbonyl derivatives, and lower molecular weight olefins continued to build up as by-products as the oxidation proceeded, as does the acidity titer. 

Analytical Degradation of Polyalkenylenes. - Microstructure characterization of polyalkenylenes via metathetical degradation with a low-molecular-weight olefin continues to be investigated.High yields of degradation products of unmodified polymers and copolymers are usually obtained in contrast, the metathesis degradation products of modified polyalkenylenes is much less reproducible, and low yields are obtained. ... 

Wittig olefinations continue to be exploited for the synthesis of heterocyclic species. For example, acylphosphoranes (65), formed as intermediates in the condensation of (trimethylsilyl)methylenetriphenylphosphorane and the silyl esters of 0-acyl(aroyl)salicylic acids, undergo intramolecular Wittig reactions producing substituted chromenones (66) (Scheme 14). " Treatment of diox-olanones (67) with (carbethoxymethylene)triphenylphosphorane produces the corresponding a,p-unsaturated esters (68), which are useful precursors to... 

Phosphorus-based olefinations continue to be the most widely used methods for the synthesis of alkenes. An understanding of most facets of the mechanism of the Wittig reaction seems to have been achieved and this has been summarised in a substantive review. Some of the principles established in these mechanistic studies can be applied to phosphorus-based olefinations other than the Wittig reaction. However, substantive mechanistic studies of phosphine oxide-based and phosphonate-based oiefinations are urgently required. A combination of the variety of phosphorus-based methods and the improved understanding of their mechanisms now aliows a substantiai degree of controi of both reactivity and stereochemistry in olefin synthesis. However, studies are required of the applications of established structure-reactivity relationships in ylides and of the various carbon and nitrogen ylide-anions recently reported. 

TABLE IX. HYDROFORMYLATION OF OTHER FUNCTIONALLY SUBSTITUTED OLEFINS (Continued)... 

Overall levels of innovation in the area this year are disappointingly low. All the various forms of phosphorus-based olefination continue to be used widely in synthesis and perhaps the relative paucity of new phosphorus chemistry is a reflection on the extent to which these methods have been developed. One area which does continue to develop, and where there is still considerable potential, is the use of phosphorus stabilised anions in enantioselective and asymmetric synthesis. Warren s continuing use of phosphine oxides and Denmark s excellent contributions to this area are especially worthy of mention. 

Carotenoids, Retenoids and Pheromones. Phosphonate-based and phosphonium ylide-based olefinations continue to be used as major synthetic methods in the preparation of vitamin A derivatives, e.g. (9Z,11Z)-vitamin A 0 and (7Z)- and (7Z,1 lZ)-vitamin A. l... 

Addition of Carbene and Carbenoids to Olefins.—The addition of carbenes and carbenoids to olefins continues to be one of the most popular routes used for cyclopropane synthesis. A review of carbenes (and nitrenes) based on the 1973 literature has appeared during the year, and methoxycarbonyl carbene has been the subject of a theoretical study. ... 

The preparation of strained olefins continues to challenge the synthetic chemist. Although the synthesis of tetra-t-butylethylene remains an elusive goal, the related tetrakis(trimethylsilyl)ethylene has now been prepared and characterized. ... 

The selectivity exhibited by an olefin metathesis catalyst for the production of -olefins or Z-olefins is a result of both kinetic and thermodynamic factors. Kinetic selectivity results from preferential formation of either syn- or anri-metallacyclo-butanes following olefin binding iy -metallacycles will undergo a cycloreversion to produce Z-olefins, whereas -olefins are derived from anfi-metallacycles. Thermodynamic selectivity arises as a result of secondary metathesis processes, in which the product olefins continue to react with the propagating catalyst. 

Improvements in the osmium-catalysed hydroxylation and oxyamination of olefins continue to appear." In the vicinal hydroxylation of olefins by t-butyl hydroperoxide earlier methods involved rather alkaline conditions, but this drawback has been overcome by using Et4NOAc instead of Et4NOH and changing the solvent from t-butyl alcohol to acetone."" Although the new method works well for base-sensitive compounds (e.g. esters), it fails with tetrasubstituted olefins. Yields are generally around 70%. Vicinal hydroxy-toluene-p-sulphonamides (8),... 

---