Unsaturated oxidation

Zeolites may behave as Lewis acids at Al,+ sites, or as Br0nsted-Lowry acids by means of absorbed H+ ions. Because they have relatively open structures, a variety of small molecules may be accommodated within the —O—Al—O—Si— framework. These molecules may then be catalyzed to react by the acidic centers. Coordinatively, unsaturated oxide ions can act as basic sites, and in some catalytic reactions both types of centers are believed to be important. Catalysis by zeolites is discussed further in Chapter 15. 

Other reactions of allyl- and vinyl-phosphine oxides include a detailed study of their intermolecular cyclization by a Friedel-Crafts-type procedure. In certain cases, the unsaturated oxides are generated in situ from /S-hydroxyalkyl(diphenyl)-phosphine oxides. Examples are given in Scheme 12 for the oxides (54)—(56). Control of double-bond position in the products of acid treatment of the oxides (57) has been achieved by using an organosilicon substituent. Thus simple alkyl... 

In two syntheses of the diol (41), the sclareol (3) has been used as a starting compound. The sclareol oxidation product, the sclareol oxide (82) [61], on bromination in methanol afforded the dibromomethoxy derivative (83) which on interaction with potassium hydroxide eliminated hydrogen bromide, giving the unsaturated oxide (84). Its successive ozonolysis and reduction of the ozonolysis products with LiAlH4 led to drimane-8a,ll-diol (41). The overall yield of the diol (41) from the sclareol (3) was ca 32% [62] (Scheme 13). 

In the other synthesis of the diol (41) from the sclareol (3) [63], the latter was ozonised according to [64], Under these conditions, a mixture of C-12 epimeric bisnorlabdanic oxidoketones (85) has been formed in a high yield. Its oxidation with monoperphtalic acid afforded a mixture of acetoxy oxides (75), from which acetic acid has been eliminated to give the unsaturated oxide (76). The latter was ozonised and the ozonolysis products were reduced with NaBffr into the diol (41). This four-step synthesis led to the diol (41) in an overall 44% yield (Scheme 14). 

Review of Sections 9.06.9 and 9.06.10 reveals that each of the l-oxa-2,5-diazine and l-thia-2,5-diazine ring systems covered in this chapter is unique with respect to degree of unsaturation, oxidation or substitution and synthetic approach, except for 677-l-oxa-2,5-diazines such as 9 (see Scheme 3) and 41 (see Figure 5). 

Di- and triacylglycerols (mainly unsaturated), oxidized triacylglycerols [25] Olive oil Coptic oil lamp shells, fourth to tenth century a.d. APCI operating in positive-ion mode, ion trap... 

---