Ring with diazo compound

C. Ring expansion of cyclic ketones with diazo compounds... 

The 1,3-dipolar addition reaction of fullerene with diazo compounds is one of the most studied reactions in the early stage of the research on fullerene chemistry [7]. The reaction in solution first affords rather labile fulleropyrazoline derivative 26, which is readily converted to the so-called 5,6-open (a bond originally shared by five- and six-membered rings cleaved) fulleroid (27) or 6,6-closed (a bond shared by two six-membered rings remaining closed) methanofullerene derivatives (28) by heat (e.g., refluxing in toluene) or photoirradiation (UV light), respectively (Scheme 11) [7a]. 

Compounds with a Si=Si or Ge=Ge bond (i.e., disilenes and digermenes) can be isolated when the double bond contains bulky substituents. Only a few cycloaddition reactions with diazo compounds are known, and two reaction modes have been observed. One of the paths leads to the formation of disiliranes 184 (242) and digermiranes 185 (243) (Scheme 8.42), probably by ring contraction of an initially formed [3 + 2] cycloaddition product. The other path involves a 1,1-cycloaddition of the diazoalkane to give disilaaziridine 186 (244) and digermaazir-idine 187 (245). This nitrene-like reactivity is rather uncommon although some intramolecular examples are known (see Section 8.6.1). 

However, the possibility of equilibrium between triazoline 4-carboxylic esters and the ring-opened diazo compounds (Section II,A,4,a) poses a problem as to which entity is actually oxidized. In fact, the open-chain tautomers formed from the addition of phenyl azide to acrylic and cinnamic esters are oxidized in good yield to the triazoles by permanganate (Scheme 119).32-28" 398 When the diazo compound is formed with ease, the oxidation is very smooth284 thus the diazo compound from the addition of phenyl or methyl azide to benzylideneacetone is oxidized rapidly in air to a triazole-4-carboxylic ester.284 A similar mechanism may be proposed to... 

The furan ring undergoes arylation with diazo compounds, but the yield is poor. Thus, furfural,23 2-furoic acid,158 and furylacrylic acid can be converted into 5-substituted arylfuran derivatives by diazo-nium salts (see further references in Ref. 159) ... 

The following types of compounds undergo coupling reactions with diazo compounds (a) Phenols, (b) Enolizable keto compounds of an aliphatic character, having a reactive methylene group which may be part of an open chain or a ring system, either homocyclic or heterocyclic. This group of compounds may be represented by the formula ... 

Diazonium intermediates have also been employed in the synthesis of pyrazoles. A convenient one-pot procedure for the preparation of 3-phenyl- or 3-pyridylpyrazoles 27 from the 1,3-dipolar cycloadditions of phenylacetylene or 3-(pyridyl)acetylene with diazo compounds 26 generated in situ from aldehydes 25 has been reported <03JOC5381>. Cyclization of ortho-(arylethynyl)benzene diazonium salts 28 having substituents at the para-position of the aryl ring furnished indazoles 29 <03TL5453>. 

The rhodiumcarbene intermediate, which is believed to be the active species in rhodium acetate catalyzed cyclopropanations with diazo compounds, shows electrophilic reactivity. Thus, diazopropenes preferentially add to electron-rich alkenes, demonstrated by the reaction of 3-diazo-l,l-dichloropropene (15) with 2-trimethylsiloxybuta-l,3-diene (16) . A mixture of Z-configurated divinylcyclopropanes 17 and rearranged dienones 18 was obtained (see also Section 1. B.2.4.5.1. for further examples of the formation of seven-membered rings such as 18). 

As mentioned before, enantioselective cyclopropanation has been known for a long time and there are other efficient catalysts for this reaction apart from dimeric rhodium(II) complexes. This is different to the cyclopropanation of alkynes with diazo compounds. Copper catalysts do not only result in lower enantiomeric excesses but also poor yields, since the high temperatures required for the reaction favor side and consecutive reactions such as the ring opening of the primary products. The improvements brought about by the use of [Rh2(55-mepy)4] (with regard to yield... 

Ring expansion with diazo compounds of N-heterocyclics... 

Arenes suffer dearomatization via cyclopropanation upon reaction with a-diazocarbonyl compounds (Btlchner reaction) [76]. Initially formed norcaradiene products are usually present in equilibrium with cycloheptatrienes formed via electrocyclic cyclopropane ring opening. The reaction is dramatically promoted by transition metal catalysts (usually Cu(I) or Rh(II) complexes) that give metal-stabilized carbenoids upon reaction with diazo compounds. Inter- and intramolecular manifolds are known, and asymmetric variants employing substrate control and chiral transition metal catalysts have been developed [77]. Effective chiral catalysts for intramolecular Buchner reactions include Rh Cmandelate), rhodium carboxamidates, and Cu(I)-bis(oxazolines). While enantioselectivities as high as 95% have been reported, more modest levels of asymmetric induction are typically observed. 

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