Unsaturated diazo ketones

Cyclopentenones (6, 67-68). Details of the Lewis acid catalyzed decomposition of /3,y-unsaturated diazo ketones to form cyclopentenones have been published. Similar decomposition of y,<5-unsaturated diazo ketones to /Ly-unsaturated cyclo-hexenones is possible, but yields are significantly lower.5... 

The construction of the tetracyclic diterpenoids has continued to attract attention. The intramolecular alkylation of an olefin by the acid-catalysed reaction of y5-unsaturated diazo-ketones has been used ° to generate ring D in the step (194)->(195) -i- (196). A benzocyclobutane route based on the thermal cyclization of (197) to (198) has been developed for the synthesis of the beyerane skeleton. A stereoselective synthesis of stachenone, based on a series of... 

Ceccherelli, P., Curini, M., Marcotullio, M. C., Rosati, O. Dirhodium tetraacetate-catalyzed decomposition of 3,Y-unsaturated diazo ketones a new entry to vinylogous Wolff rearrangement. Gazz. Chim. Ital. 1994,124,177-179. 

Bis(acetylacetonato)nickel(II) has been recommended as a homogeneous catalyst for intramolecular cyclopropanation reactions of unsaturated diazo ketones(see Section 1.2.1.2.4.2.6.3.4.). As the experiments were carried out, without exception, by irradiating the diazo ketone at elevated temperature in the presence of the catalyst, the actual significance of the catalyst is, however, unclear. 

Bicyclo[3.1.0]hexan-2-one and bicyclo[4.1.0]heptan-2-one were obtained from the corresponding unsaturated diazo ketones with 75 and 95% ee, respectively, when the chiral bis(semicorrinato)copper(II) catalyst developed by Pfaltz (see Section 1.2.1.2.4.2.6.3.2.) was used, ° whereas Aratani catalysts, in general, provided low to moderate enantioselectivities for these transformations. " Modest ee-values (35-40%) were also observed when the Pfaltz catalyst was applied to unsaturated /1-keto-a-diazo esters such as methyl 2-diazo-3-oxohept-6-enoate and -oct-7-enoate. ° ... 

Intramolecular cyclopropanations with unsaturated diazo ketones have also been reported. Furthermore, enantioselective cyclopropanation with diazomethane can be achieved in up to 75% ee. In detailed mechanistic discussions, a copper(I) species, complexed with only one semicorrin ligand, and formed by reduction and decomplcxation, is suggested as the catalytical-ly active species, cisjtrans Stereoselection and discrimination of enantiotopic alkene faces should take place within a copper-carbene-alkene complex25-54"56. According to these interpretations, cisjtrans selectivity is determined solely by the substituents of the alkene and of the diazo compound (especially the ester group in diazoacetates) and is independent of the chiral ligand structure (salicylaldimine or semicorrin)25. 

In another example, rhodium carboxylates, chirally modified with mandelate or proline-derived compounds, were used in intramolecular cyclopropanation of unsaturated diazo ketones (e.g., 4) to give bicyclo[3.1.0]hexanonc products in 97% yield with 12% ee7f>. 

The photoelimination of nitrogen from diazoketones and the fate of the resulting species are still subjects of major interest. A successful photochemically induced Wolff rearrangement of an acyclic /Sy-unsaturated diazo-ketone in aqueous dioxan has been reported.60 In the photodecomposition of the diazo-ketone... 

In a series of papers Smith and his coworkers investigated the mechanism of a rearrangement which can take place when a rearranged acid 258 is formed from an unsaturated diazo ketone 257 during the Arndt-Eistert reaction. The reaction was promoted by CUSO4, Cu(AcAc)2 or Cu(OTf)2 in the presence of various alcohols. 

Bp3-OEt2 catalyzes the decomposition of /3,y-unsaturated diazomethyl ketones to cyclopentenone derivatives (eq 37). Similarly, y,i5-unsaturated diazo ketones are decomposed to /3,y-unsaturated cyclohexenones, but in lower yields. ... 

Lewis acids are also effective in activating a-diazo ketones towards intramolecular nucleophilic attack by alkenes and arenes. The reaction has been used effectively for the synthesis of cy-clopentenones (eq 27) starting with 8, /-unsaturated diazo ketones derived from the corresponding acid chloride and diazomethane. It has also been used to initiate polyalkene cyclizations (eq 28). Typically, boron trifluoride etherate is used as the Lewis acid, and electron-rich alkenes are most effective providing the best yields of annulation products. 

Smith and Dieter have demonstrated that /8y-unsaturated diazo-ketones, previously employed in the synthesis of cyclopentenones, may possess considerable potential as polyene cyclization initiators (Scheme 26) and Sutherland et al. have reported an efficient synthetic route to the aldehyde (117) capable of Wittig-Schlosser condensation affording substrates for epoxyolefin cyclization. ... 

Cu(OTf)2 is the reagent of choice for intramolecular cyclization of /3,)/-unsaturated diazo ketones to cyclopentenones (eq 8) and for intramolecular cyclopropanation of y,5-unsaturated diazo ketones (eq 9)7... 

Angularly functionalized polycyclic systems may be prepared from /3,)/-unsaturated diazo ketones by a vinylogous Wolff rearrangement in the presence of coppCT(II) triflate. Dry copper(II) acetylacetonate is equally suitable. 

One of the earliest uses for rhodium(II)-catalyzed dipoles was demonstrated in Davies furan synthesis [22]. Isomiinchnones were also shown to produce substituted furans [115]. Additional furan syntheses have been described using silylacetates [116], unsaturated esters [117], and fluoroalkyl diazo acetates [118]. The synthesis of furofuranones and indenofuranones 35 from a-diazo ketones having pendant alkynes has also been reported (Eq. 6) [119]. Other fused heterocyclic systems include furo[3,4-c]furans [120, 121] furo[2,3-b]furans [122] as well as thiobenzofurans [123], and benzoxazoles[124] have also been synthesized with this methodology. 

With 0,-y-unsaturated a -diazo ketones, the resulting [2.1.0]-bicyclic systems (40) were quite unstable and underwent a [2 + 2] cycloreversion to generate ketenes (41), which were then trapped by nucleophiles (Scheme 7). The overall scheme has been named a vinylogous Wolff rearrangement and offers a novel entry to products usually derived from a Claisen rearrangement.102 A recent report describes its application for functionalized angular alkylation in fused ring systems.103 In contrast, the intramolecular re-... 

A reaction between a-diazo ketones and a,(1-unsaturated aldehydes under rhodium(ll)-catalysis provides a route to epoxy-bridged tetrahydropyran-4-ones <2002JOC8019>. This methodology allows entry to functionalized spiro-dioxa-bridged polycyclic frameworks <2002TL3931, 2003T8117>. 

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