Epoxy hydrazones

Cleavage of carbonyl-containing selenoxides and sulfones Fragmentation of epoxy hydrazones Rearrangement of vinylic hydroxycyclopropanes Rearrangement of 3-hydroxy-1,5-dienes (oxy-Cope)... 

Fragmentation of a.fJ-Epoxy Hydrazones Eschenmoser-Tanabe ring cleavage... 

Wharton reaction2 (1, 439-440). This rearrangement of a,3-enones to allylic alcohols via an epoxy hydrazone has seen only occasional use outside of the sterol field because yields can be low. Some expedients have been shown by Dupuy and... 

Luche to improve the yield. When the intermediate epoxy hydrazone is isolable, addition of a strong base, potassium r-butoxide or potassium diisopropylamide (KDA), improves the yield. Triethylamine is the base of choice in the case of an unstable epoxy hydrazone (equation I). 

P-Hydroxy tosylhydrazones, which are the products of a conventional aldol reaction between a dilithi-ated tosylhydrazone reagent and an aldehyde, can also be prepared by alternative routes. For example, Stork and Ponaras have described a procedure whereby an epoxy ketone is converted into an epoxy hydrazone. Subsequent addition of an alkyl- or aryl-magnesium bromide followed by hydrolysis yields either an a-alkyiated- or a-arylated-p-hydroxy ketone or an a,p-unsaturated ketone. Since the attack of the Grignard reagent on the epoxide occurs with inversion at the a-carbon, this reaction can be used to... 

Addition-fragmentation, a,/3-Epoxy hydrazones react with Grignard reagents to afford allylic alcohols. 

Cyclic a,p-unsaturated ketones can be cleaved by treatment with base of their epoxy tosylhydrazone derivatives to give acetylenic ketones. The reaction can be applied to the formation of acetylenic aldehydes (R=H) by using the corresponding, 2,4-dinitrotosylhydrazone derivatives.Hydrazones (e.g., 47) prepared from... 

Fragmentation of a,P-epoxyketones via the intermediacy of a,P-epoxy sulfonyl-hydrazones. 

Groups of reportedly photochromic systems which deserve further study include (a) disulfoxides (123,124), (b) hydrazones (125-129), (c) osazones (130-133), (d ) semicarbazones (134-143), (e) stilbene derivatives (144), (/) succinic anhydrides (145-148), and (g) various dyes (149,150). A number of individual compounds also remain unclassified as to their mechanism of photochromic activity. These include o-nitro-benzylidine isonicotinic acid hydrazide (151), 2,3-epoxy-2-ethyl-3-phenyl-1-indanone (152), p-diethyl- and p-dimethyl-aminophenyli-minocamphor (153), brucine salts of bromo- and chloro-nitromethionic acid (154), diphenacyldiphenylmethane (155,156), 2,4,4,6-tetraphenyl-1,4,-dihydropyridine (155,156), 2,4,4,6-3,5-dibenzoyltetrahydropyran (155,156), o-nitrobenzylidenedesoxybenzoin (157), p-nitrobenzylidene-desoxybenzoin (157), N-(3-pyridyl)sydnone (158,159), tetrabenzoyl-ethylene (160), and the oxidation product of 2,4,5-triphenylimidazole (161,162). 

A 2-cyclohexenone derivative can be transformed into the corresponding epoxy tosyl-hydrazone by sequential treatment with peracid and tosylhydrazine. The elimination of nitrogen and p-toluenesulfinate and fragmentation after rearrangement to the 3-tosylazo allylic alcohol may occur under mild conditions. Carbonyl compounds with 5,6-triple bonds are formed in high yields (J. Schreiber, 1967 M. Tanabe, 1967). If one applies this reaction to a 9,10-epoxy-1-decalone, a ten-membered 5-cyclodecyn-l-one ring is formed (D. Felix, 1971). This product is an important intermediate in the perfume industry and has been used on a large scale. For this purpose Eschenmoser developed a synthesis in which the readily removed styrene was split off instead of a sulfmic acid. Thus a l-amino-2-phenylaziridine hydrazone was used instead of a tosylhydrazone (D. Felix, 1968). ... 

C(6) [14] and C(7) tosylhydrazones [2y] in contrast gave the A - and A -olefins respectively. A i4a-hydroxy-i7-tosyl-hydrazone (5) reacted with C(i8>"methyl migration and participation by the hydroxyl group to form the i3a,i4a-epoxy derivative (6) [28]. All these reactions can be accommodated by a carbonium-ion mechanism (see below). 

Epoxides will fragment if carbanions are formed adjacent to the epoxide ring. Decomposition of the hydrazone of an epoxy ketone in the presence of base may lead to an allylic alcohol (Scheme 2.24). Since the epoxy ketone may be prepared from an unsaturated ketone, this can form part of a sequence for the 1- 3 transposition of an oxygen function. 

A useful reduction reaction takes place with hydrazine in the presence of a strong base. In the Wolff-Kishner reduction a carbonyl group is reduced to a methylene. If the hydrazone is formed from an epoxy ketone, the decomposition takes place easily with the formation of an allylic alcohol. 

The Eschenmoser fragmentation uses a tosyl hydrazone of an cr,/S-epoxy-ketone (p. 1008). epoxide can be made with alkaline hydrogen peroxide and the tosylhydrazone needs tosylhydrazine to form what is simply an imine. Then the fiin can begin. The stereochem y doesn t matter for once. 

The formation of epoxy ketones from sterically crowded enones is often difficult. Avoiding the epoxi-dation step, fragmentation to give the alkynone (137 Scheme 47) occurs on treatment of the unsaturated hydrazones (145) (from 135) with an excess of NBS in methanol. Ohloff and Buchi used this sequence for a further synAesis of exaJtone (118) and muscone (119). 

Eschenmoser-Tanabe fragmentation Formation of alkynals or alkynones from epoxy ketone hydrazones. 158... 

Eelix, D., Schreiber, J., Piers, K., Horn, U., Eschenmoser, A. New version of epoxy ketone-> alkynone fragmentation. Thermal decomposition of hydrazones from a,P-epoxycarbonyl compounds and W-aminoaziridines. Helv. Chim. Acta 1968, 51, 1461-1465. 

Substitution in the a-position of an a,3-unsaturated ketone can be achieved by addition of an alkyl or aryl Grignard reagent to an a,3-epoxy N,N-dimethyl hydrazone.22-23 qj3... 

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