Isoxazolones, benzylidene

An effect of high pressure on the diastereoselectivity is also observed for intramolecular hetero Diels-Alder reactions as found for the cycloaddition of the benzylidene-isoxazolone 8-23 to afford the cis-annulated 8-24 as the major product together with the frans-diastereomer 8-25 (Fig. 8-8) [549], However, the difference in activation volume with AAV =1.6 0.2 cm3 mol"1 is rather small. The activation volume with AV = 19.6 0.5 cm3 mol-1 at 343 K lies significantly below the usual values found for intermolecular cycloadditions of 1-oxa-1,3-butadienes, indicating that this reaction may be on the border line to a two-step reaction but see also below. 

Pyrazolones (154) and isoxazolones (155) can also be used in the Knoevenagel reaction. Thus condensations with aliphatic aldehydes, aromatic aldehydes and ketones in the presence of ethylenediammon-ium diacetate or other typical catalysts provide the corresponding alkylidene and benzylidene compounds in good yields (for stereochemistry see Section 1.1A new method involves the use of dicyclohexylcarbodiimide at 20 C without an additional catalyst. ... 

Hydrazino-5,6-diphenyl-l,2,4-triazine (289) reacts with 4-benzylidene-2-phenyl-5(4//)-oxazo-lones (290) and 4-benzylidene-3-methyl-5(4//)-isoxazolones (291) in toluene to products (292), (293) substituted in the hydrazino group, the first by acylation by the oxazolone, the second by arylraethylidene group transfer (Scheme 53) <88JHC1813>. 

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