No abstract

Treatment of 2,3,3-trimethyl-4-pentenal phenylhydrazone in refluxing ethylene glycol led to l-(3-methylbut-2en-1-yl) -3-methylindole, presumably through allylic rearrangement to the indolic nitrogen of the intermediate 3-(1,1 -dimethylallyl) -3-methylindolenine; no rearrangement to a 4-allylindole derivative was observed. Treatment of l,3-cyclohexanedione-2-chloro-6-(3-methylbut-2-en-l-yl) phenylhydrazone in refluxing o-dichlorobenzene led to 5-allyl-7-chloro indole derivatives, while in aqueous sulfuric acid a 4-alkyl-7-chloro indole derivative was obtained. These derivatives presumably arise via rearrangement of a C-3a isoprenylated intermediate. The formation of these products is discussed in relation to ergot alkaloid biosynthesis.

Reaction of methoxyvinyllithium (MVL) with aliphatic and aromatic esters gives, via an isolable divinyl ether intermediate, 3-hydroxy-2,4-pentanediones, which with hydrazine yield the previously unknown 4-hydroxyisopyrazoles. The stereochemistry of their facile thermal rearrangement to 2-pyrazolin-4-ones has been studied.Recently we described the convenient acyl anion equivalent methoxyvinyllithium (MVL) and some of its reacti0ns.l-3 I n the course of a study of the reactions of MVL with esters we hydrolyzed the initial adducts 1 t o t h e hydroxy diones, as 2,l and then treated these substances with hydrazine in alcohol R, P H R, P H Me0 * OMe 1 * 0 0 2 t o furnish the previously unknown 4-hydroxyisopyrazoles 3. These isopyrazoles 3 were thermally unstable, undergoing a smooth conversion t o t h e 2-pyrazolin-4-ones 4 (cf. Table I) R\ PH 0 II N-N N-NH 3 4 R = a l k y l phenyl a t relatively low temperature (ca. 100 "C). This reaction is undoubtedly related t o the van Alphen-Hiittel rearrangement of geminally disubstituted pyrazolenines.P6 Thus van Alphen observed the conversion of the pyrazolenine 5 t o a substance thought to be 6 in acetic acid a t 100 0C.4 However, it was subsequently shown t h a t this was in fact the isopyrazole 7 Me,OF Yh M e 2 0 C h ; : + Me,OC+Ph N=N N-N / COzMe 5 6 Ph C0,Me ?Y Me,OC N-N 7 which could also be obtained by simply heating 5.6 These later authors6 described this reaction as a thermal [1,5] sigmatropic change, which in the suprafacial mode should proceed with retention of configuration of t h e migrating group,7 Scheme I. A similar [1,5]-sigmatropic shift is reasonable for the purely thermal rearrangement of the 4-hydroxyisopyrazoles 3, which Scheme I followed by a tautomerization provides the 2-pyrazolin-4-ones, Scheme 11. In order to examine t h e stereochemistry involved Scheme I1 in this [1,5] shift we required a simple degradation of the rearrangement products and t o this end examined some possible routes. An attempted ring cleavage reaction on t h e N-chloro derivative 8, generated by reaction with tert-butyl hypochlorite (-78 "C), gave, by action of ethanolic sodium ethoxide, the ether 9, presumably by way of t h e dehydropyrazole 10. Lithium aluminum hydride reduction of t h e pyrazolone 35% \ c1 E t 0 & H 9 10 8 11 took an unexpected course, giving cleanly t h e dealkylated pyrazole 12 and presumably isobutylene. A reasonable precursor of 12 might be the deoxygenated isopyrazole 13 as its 0 aluminum complex. This same reductive dealkylation was observed in the sec-butyl substituted analogue of pyrazolone 11. Eventually we were successful in establishing a stereochemical cycle which related the stereochemistry of the purely thermal [1,5]-sigmatropic shift t o a [1,2] shift of t h e type characteristic of alkyl migration t o an electron-deficient terminus. This is described in Scheme 111. T h u s the optically active isopyrazole 14, obtained from (+)-methyl a-methylbutyrate, was thermally rearranged (110 "C, 3 min) t o t h e pyrazolinone 15 and then converted, sequent...

Zur Einführung des Dihydroxy‐acetonrestes dient das Methoxyvinyllithium (II).

Bei der Umsetzung verschiedener Ester (I), z.B. den Methylestern der Valerian‐, Pivalin‐, Benzoe‐ oder (+)‐a‐Methyl‐buttersäure, mit Methoxyvinyllithium (II) entstehen Bis‐enoläther (III), die zu den 2‐Hydroxy‐1,3‐diketonen (IV) gespalten werden können.