Addition of diazomethane to enones

The addition of diazomethane to unsaturated esters (1), as ethyl acrylate, methyl crotonate and ethyl cinnamate, was investigated by Auwers who showed that the primary addition product is a A -pyrazoline (2) which rearranges spontaneously to the conjugated A -pyrazoline (3). 

However, in the case of a-substituted unsaturated esters (4), as for example methacrylic or tiglic acid esters, diazomethane addition results in the formation of stable A pyrazolines (5). The latter products require halogen acids for conversion to the isomeric nonconjugated A -pyrazolines (6). 

Stereospecific addition of diazomethane is observed with dimethyl di-methylmaleate (7) and dimethyl dimethylfumarate (10).  

Pyrolysis at 190° of the resulting diastereomeric A -pyrazolines (8) and (11) leads to elimination of nitrogen and formation of the cis- and tmns-cydo-propanecarboxylates (9) and (12), respectively. Thermal decomposition of the A -pyrazoline (13) affords methyl tiglate (14) in addition to the cyclopropane derivative (15) in a ratio 2 1, while A -pyrazolines such as (3) give only 0L,[i- or, y-unsaturated esters, and no cyclopropane derivatives. 

The addition of diazomethane to a,/l-unsaturated ketones, e.g., benzalace-tone and benzalacetophenone, results in A -pyrazolines (16) which decompose thermally to the conjugated ketones (17). Cyclopropane formation is not observed in this instance. 

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Birch reduction, followed by acid treatment and addition of diazomethane leads to the A9(11)-enone 159 in 41% yield. Then, the double bond is hydrogenated and, by using PhSeCl and hydrogen hydroperoxide, the double bond A13 is formed. Treatment of the enone with lithium disopropylcuprate-dimethyl sulfide complex gives an intermediate enolate that is trapped again using PhSeCl. Enone 160 is obtained via oxidative elimination (62%). 

The grevillins are easily converted into crystalline yellow peracetyl derivatives with acetic anhydride and a trace of concentrated sulphuric acid (Table 2) 204, 461, 603). On catalytic hydrogenation the grevillins yield colourless dihydro derivatives in which reduction of the exocyclic double bond has taken place 603). Conjugate addition of nucleophiles to the exocyclic enone system leading to colourless by-products has also been observed during acetylation of these pigments 101) and in their reaction with diazomethane in methanol 276, 461). 

Many enone systems readily undergo 1,3-dipolar addition reactions. This applies to steroids, as illustrated by the formation of the fused pyrazole 16-4 from reaction of the enone 16-2 with diazomethane. Pyrolysis of that pyrazole results in extrusion of nitrogen to leave behind a methyl group at position 1 (16-5). 

The product (6-4) from that sequence, which is of course simply 6-methyldios-genin, is then subjected to a series of degradation reactions as those used for the parent compound to give the 6-methyl derivative (7-1) of dehydropregnenolone. Reaction of the enone function of that product with diazomethane leads to 1,3-dipolar addition and the formation of the pyrrazoline (7-2). That intermediate loses... 

By Cyclopropanation. 2-Cyclohexenone reacts with diazomethane in the presence of catalytic Pd(OAc)2 to give the expected cyclopropyl ketone (eq 119) and this process represents an especially useful way of preparing such systems. However, when the enone carries an amide unit at the y-carbon, a competing pathway, commencing with diazomethane addition to the carbonyl group, is observed. Under acidic conditions, tetrahydrobenzoxa-zoles are the observed products of reaction (eq 120). ... 

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