Diazoalkanes ring expansion

History of Diazoalkane Ring Expansion and Chain Extension Reactions. 115... 

The reaction of diazomethane with a,p-xmsaturated carbonyl compounds under classical protic conditions has been shown to produce pyrazoline products arising from 1,3-dipolar cycloaddition [3, 4]. Limited examples of a,p-xmsaturated carbonyl substrates undergoing ring expansion in the presence of Lewis acid promoters have been reported. It was not until the introduction of Lewis acids for diazoalkane ring expansion that these types of substrates were even reactive. In Drege s... 

Ready extrusion of sulfur dioxide from fused thiirane dioxides is well known and was observed in the formation of pyrazoles from 19b and diazoalkanes - . A ring expansion... 

Trimethylaluminum also promotes ring expansion by diazoalkanes.81... 

Quinazolinium salts, e.g. (189) or its 4-oxo analogue, on treatment with diazoalkanes also undergo ring expansion to give 1,4-benzodiazepines (74BCJ343). 

Isatin and N-substituted isatins react with diazoalkanes to give a variety of products. Simple adducts of the type 181 have been obtained when N-substituted isatins react with methanol-free diazomethane and are reported to lose nitrogen and react further in methanol.505 Such adducts have also been reported in other cases.196,506-508 Ring enlargement to quinolones (182 R is the R in RCHN2 and R is usually OH but sometimes OMe from diazomethane) frequently occurs.123,196,506-509 Finally, epoxides of the type 183 have sometimes been obtained from the diazoalkane reaction.123,249,507,510 With diphenyldiazomethane, ring expansion does not take place and 183 (R = Ph) is the only... 

Finally, ring expansions of cyclic ketones are an important method for the preparation of carbocyclic systems. Diazoalkanes allow this reaction to occur and involve C—C bond formation. When combined with carefully chosen organoaluminum compounds, this process can be performed in a highly stereoselective fashion (equation 148)541. 

Diazoalkanes, such as diazomethane460 and diazoarylalkanes461,462 add to isatin at the C-3 position, leading to a carbinol that suffers a ring expansion to give the corresponding quinolone463 (Scheme 111). 

Zizaene sesquiterpenes were the subject of considerable synthetic interest in the 1970s and several synthetic strategies to construct the tricyclo[6.2.1.0 ]undecane skeleton involved an intramolecular diazoalkane-carbonyl ring expansion, an intramolecular magnesium-ene reaction, and a titanium-promoted reductive coupling. - ... 

Finally, epoxides of the type 183 have sometimes been obtained from the diazoalkane reaction.With diphenyldiazomethane, ring expansion does not take place and 183 (R = Ph) is the only... 

A diazo ester or alkane will react with a ketone, under Lewis acid catalysis, to give the homologated product. This reaction is most often used for one-carhon ring expansion, as illustrated hy the conversion of (166) to (167 equation 69). The regioselectivity of the (166) to (167) transformation, 98 2 in the example illustrated, was found to depend on both the diazoalkane and the Lewis acid used. With diazomethane and boron trifluoride, a 1 1 mixture of regioisomeric products was observed. 

The homologation of ketones by the addition of diazoalkanes complements the Tiffeneau-Demjanov rearrangement. Epoxide formation is a side reaction which can be minimized if polar aprotic solvents are avoided (Scheme 7). Rearrangement i.e. homologation) is maximized in ether solvents or by Lewis acid catalysis. The reaction is most effective in the ring expansion of cyclic ketones. 

In some cases diazoalkane, quinone adducts give seven-membered ring (ring-expanded) products on deazetization rather than a simple cyclopropanation product and ring-expansion products also dominate in attempts to add to the 3,4-double bond of coumarins. ... 

Ring expansion of a number of (cyclopropenyl)diazoalkanes gives cyclobutadiene derivatives, e.g. reaction of 7, though in some cases, fragmentation occurs leading to alkynes (see Section 10.A.2.2.). ° There is evidence that the cyclobutadienes are formed through singlets, while the alkynes are derived from triplets. 

A novel ring expansion of l-alkyl-3-aryl-4-oxoquinazolinium salts was achieved, by the insertion of the a-carbon atom of diazoalkanes, in alcoholic solutions [Eq. (14)]. Ethyl diazoacetate also added across the 1,2 double bond, but unlike simple diazoalkanes the adduct 110 did not rearrange. ... 

As with other diazoalkanes, diazomethane reacts with alkenes to form cyclopropane derivatives (sec. 13.9.C.i).272 Reaction with aromatic derivatives leads to ring expansion to cycloheptatriene derivatives.223 Both of these reactions (addition to an alkene or arene insertion) involve generation of an intermediate carbene and addition to a jt bond they will be discussed below. Many of the reactions of diazomethane tend to be ionic in nature and are, therefore, set aside from the other diazoalkane chemistry in this section. One of the commonest uses of diazomethane itself is esterification of small quantities of acids, especially acids that are precious for one reason or another. The reaction is quantitative and gives good yields of a single product, as in Tadano s conversion of 338 to the methyl ester of 339224 in a synthesis of (-)-verrucarol. 

Tabk 1 Ring Expansion of Bridged Bicyclic Ketones with Diazoalkanes or Tiffeneau-Demjanov Rearrangement... 

Recourse to an alcohol cosolvent was the premier means of accelerating diazoalkane-based ring expansion reactions for more than half a century. Alkyl diazomethanes were prepared by base-catalyzed decomposition (for further... 

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