Aryl diazoacetates

Highly enantioselective intermolecular C-H insertion into cyclohexane and cyclopentane is possible using the Rh2(S-DOSP)4 carbenoids generated from aryl diazoacetates 172 to form 173 (Eq. 21) [121, 130]. The enantioselectivity is enhanced when the reactions are conducted at lower temperatures, without any deleterious effect on the catalytic activity or product yield [130]. Extending the reaction to other cyclic and acyclic hydrocarbons has revealed a dehcate balance required between the steric environment and the electronic state of the carbon undergoing C-H insertion [130]. The decreasing enantioselectivity and yield of C-H insertion into adamantane 174 (67% yield, 90% ee). 

Double cyclopropanation of furans and pyrroles with aryl diazoacetates catalysed by Rh2(S-DOSP)4 have been reported to occur with opposite stereochemistry depending on the nature of the heterocycle.55 Better yields and ees are achieved for tricycles (69) derived from furan than for (68) derived from more bulky pyrroles. Monocyclo- propanation (with high yields and ees) is achieved on the furan ring of benzofuran, whereas double cyclopropanation of the indole is observed. 

A three-component reaction of aryl diazoacetates, alcohols, and araldehydes (or araldimines) has been investigated, using a rhodium(II) catalyst.283 The first two components combine in the presence of catalyst to produce a zwitterion (72a). Evidence for equilibration with an alcoholic oxonium ylide intermediate (72b) is presented. It is proposed that this species is trapped by electron-deficient araldehyde (or imine) to give new C-C bond formation. 

Several silver complexes have been investigated in C-H insertion reactions of carbenes. One of the earliest reports by Sulikowski and Burgess describes an intramolecular C-H insertion of a chiral aryl diazoacetate 80 as part of a study on the total synthesis of mitomycin family of natural products (Scheme 8.15).41 Among several catalysts that were screened was AgSbly, in the presence of bis(isoxazoline)-type ligands, which led to the formation of the desired insertion product 81 in moderate yield and modest diastereoselectivity. 

Other reactions. iV-BOC-protected azocane 281 was reacted with aryl diazoacetate 282 in the presence of 1 mol% of dirhodium tetraprolinate catalyst to produce a very efficient C-H insertion with a high diastereoselectivity and enantioselectivity (Scheme 118 <2003JA6462>). The erythro C-H insertion product 283a was formed in 90% ee and 90% de, which infers that the flexibility of the eight-member ring sterically favors the accommodation of the transition state for the C-H activation. 

Biaryls are produced in low yields by several related coupling reactions. When benzenediazonium chloride is treated with aqueous sodium hydroxide in the presence of benzene, nitrogen is eliminated and biphenyl is formed in 22% yield. Better results are sometimes obtained when the sodium hydroxide is replaced by sodium acetate or when stabilized diazonium salts are employed. In the former modification the aryl-diazoacetate, ArN = NOCOCHj, is an intermediate product. The tautomeric forms of the aryldiazoacetates are N-nitrosoamides, ArN(N0X30CH, which are obtained by the action of nitrous fumes or nitrosyl chloride on... 

Significant levels of enantiocontrol were also observed in the Rh2(2S-DOSP)4 catalyzed reaction of aryl diazoacetates with tetrahydrofuran where C-H insertion occurred exclusively at the 2-position, Eq. (31) [51]. Two diastereoisomeric products, (21) and (22), are formed, with a preference for isomer (21) and comparable levels of enantioselectivity in each ((21) 52-76% ee (22) 51-71% ee). It is premature to assess the general efficacy of catalyzed asymmetric intermolecu-lar C-H insertion. Prehminary studies by Davies and Hansen [51] suggest that enantiocontrol may be very substrate dependent. For example, the vinyl diazocarbonyl precursor in Eq. (32) and cyclohexane with Rh2(2S-DOSP)4 as catalyst react with an enantioselectivity (83% ee) comparable to that obtained with aryl diazoacetates, whereas diazoacetoacetates when treated similarly, show very minor levels of enantiocontrol (3% ee) in Eq. (33). 

Decomposition of an aryl diazoacetate by CuOTf in the presence of a conjugated carbonyl compound leads to a 2,3-dihydrofuran-2-carboxylate, the result of a formal [4+ IJcycloaddition. To acquire a chiral product the presence of bipyridyl 144 is needed. ... 

The tandem ylide generation/[2,3]-sigmatropic rearrangement can also be performed with sulfur and iodonium ylides and in these cases the reaction can proceed in intermolecular fashion.For example, up to 78% ee has been obtained in the reaction of allyl-2-methylphenyl sulfide (9.129) with aryl diazoacetates such as (9.130) in the presence of the copper catalyst generated with bis-oxazoline (9.07), while the reaction of aUyl iodide (9.132) with ethyl diazoacetate yields product (9.133) with 69% ee using this complex. ... 

X. Zhang, H. Huang, X. Guo, X. Guan, L. Yang, W. Hu, Angew. Chem. Int. Ed. 2008, 47, 6647-6649. Catalytic enantioselective trapping of an alcohohc oxonium yhde with aldehydes Rh VZr -cocatalyzed three-component reactions of aryl diazoacetates, benzyl aleohol and aldehydes. 

Davies et al. carried out a comparative study on the catalytic activities of Rh2(S-DOSP)4 (3), RhjlR-BNP)4 (4), and Rh2(S-PTAD)4 (5) toward asymmetric cyclopropanation reactions (Table 9.2, entries 3-9) [94]. In general, Rh2(S-DOSP)4 was found to be the most effective catalyst for asymmetric intermolecular cyclopropanation of methyl aryldiazoacetates with styrene. Rh2(S-PTAD)4 exhibited lower levels of enantioinduction with 4-substituted aryldiazoacetates but it proved to be superior with the 4-methoxy substituted aryldiazoacetate (Table 9.2, entry 4, 96% ee) [94, 98]. Rh2(i -BNP)4, however, functions as an extremely effective catalyst with all the aryldiazoacetates substituted with three methoxy groups (88-97% ee). The asymmetric inductions varied with the aryl groups on the aryl diazoacetate but the choice of olefin had no effect on the selectivity. 

Independent from Liu and coworkers, we have found and reported that alkyl and aryl diazoacetates can be polymerized by the initiation with palladium dichloride (PdCh) in the presence of amine such as pyridine and triethylamine [38]. Poly(ethoxycarbonylmethylene) and poly(methoxycarbonylmethylene) were obtained in 50 100% yields by the polymerization of ethyl diazoacetate (EDA) and... 

When an aryl diazoacetate with bulky substituents on its phenyl ring was employed as a monomer and the product obtained by initiation with PdCh/EtsN was analyzed by MALDI-TOF-MS in reflector mode, the result suggested the presence of diethylamino groups at both polymer chain ends [38] (Scheme 13). 

Scheme 19 (NHC)Pd/borate-initiated polymerization of aryl diazoacetates...

A Hammett eorrelation analysis was made on the Si-H insertion of aryl diazoacetates 1 with triethylsilane in the presence of Rh(II) eatalysts, as shown in Scheme 21.2. 

Synthesis of (+)-Sertraline, (-)-Colombiasin A, and (—)-Elisapterosin B While the aryl diazoacetates and 1,3-cyclohexadiene in the presence of dirhodium (II) car-boxylate as catalyst gave the product of C-H insertion, the aryl vinyl diazoacetates did not lead to the expected C-H insertion product but to a combined C-H insertion/Cope... 

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