1,3,4-Oxadiazole, 2,5-diphenyl-, synthesis

Lee RH, Hsu HF, Chan LH, Chen CT. Synthesis and electroluminescence properties of a novel tetraphenylsilane-oxadiazole-diphenyl(para-tolyl)amine polymer. Polymer 2006 47(20) 7001-12. 

Acyl nitroso compounds react with 1, 3-dienes as N-O heterodienophiles to produce cycloadducts, which have found use in the total synthesis of a number of nitrogen-containing natural products [21]. The cycloadducts of acyl nitroso compounds and 9,10-dimethylanthracene (4, Scheme 7.3) undergo thermal decomposition through retro-Diels-Alder reactions to produce acyl nitroso compounds under non-oxidative conditions and at relatively mild temperatures (40-100°C) [11-14]. Decomposition of these compounds provides a particularly clean method for the formation of acyl nitroso compounds. Photolysis or thermolysis of 3, 5-diphenyl-l, 2, 4-oxadiazole-4-oxide (5) generates the aromatic acyl nitroso compound (6) and ben-zonitrile (Scheme 7.3) [22, 23]. Other reactions that generate acyl nitroso compounds include the treatment of 5 with a nitrile oxide [24], the addition of N-methyl morpholine N-oxide to nitrile oxides and the decomposition of N, O-diacylated or alkylated N-hydroxyarylsulfonamides [25-29]. 

Phenyl tetrahydrophthalimides represent the third class of early Protox herbicides. They were introduced in the early 1970s, after the diphenyl ether and l,3,4-oxadiazol-2(3H)-one chemistries. Following the introduction by Mitsubishi of chlorophthalim (3) [27] in 1972, incorporation of the 2,4,5-trisubstituted-phenyl pattern in the 1980s resulted in the synthesis of highly active molecules such as S-23142 (12) [45], and S-23121 (20) [45, 56] (Fig. 3.8). 

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