Tert-Butyl diazoacetate, cyclopropanations

Katsuki has recently constructed a series of chiral Co(III)-salen complexes 30 and used them as catalysts for cyclopropanation of styrene using tert-butyl diazoacetate [78], Not only is enantiocontrol for addition greater than 90% ee, but diastereoselectivity favors the trans-... 

Aryl-5,5-bis(oxazolin-2-yl)-l,3-dioxanes 169 have been easily prepared in three steps from diethyl bis(hydroxymethyl)malonate, amino alcohols, and aromatic aldehydes. They have been used for the copper-catalyzed asymmetric cyclopropanation of styrene with ethyl diazoacetate in up to 99% ee for the trawx-cyclopropane (maximum transicis ratio = 77/23) <05TA1415>. The same reaction performed on 2,5-dimethyl-2,4-hexadiene with tert-butyl diazoacetate in the presence of copper catalysts bearing ligand 170, prepared from arylglycines, exhibited remarkable enhancement of the rrawx-selectivity (transicis ratio = 87/13), with 96% ee for the trans product <05JOC3292>. 

Ishitani and Achiwa [16] have recently prepared an axially disymmetric rhodium (11) biphenylcarboxylate catalyst, Rh2(S-BDME)4 of Fig. 2, and found that although the transxis diastereoselectivity in its catalysis of the styrene-EDA reaction was poor, the enantiocontrol was better than that observed with the pro-linate catalyst. The biphenyl based catalyst yielded an 87% ee for the cyclopro-panation of 2-naphthylethene and tert-butyl diazoacetate, though again the diastereoselectivity was very low. Use of an additional chiral auxiliary in the diazoester as in the d-menthyl derivative in Eq. (10) furnished a mixture of cyclopropanes, the cis-isomer of which was found to have an ee of 99%. 

Dirhodium(ll) tetrakis[methyl 2-pyrrolidone-5(R)-oarboxylate], Rh2(5R-MEPV)4, and its enantiomer, Rh2(5S-MEPY)4, which is prepared by the same procedure, are highly enantioselective catalysts for intramolecular cyclopropanation of allylic diazoacetates (65->94% ee) and homoallylic diazoacetates (71-90% ee),7 8 intermolecular carbon-hydrogen insertion reactions of 2-alkoxyethyl diazoacetates (57-91% ee)9 and N-alkyl-N-(tert-butyl)diazoacetamides (58-73% ee),10 Intermolecular cyclopropenation ot alkynes with ethyl diazoacetate (54-69% ee) or menthyl diazoacetates (77-98% diastereomeric excess, de),11 and intermolecular cyclopropanation of alkenes with menthyl diazoacetate (60-91% de for the cis isomer, 47-65% de for the trans isomer).12 Their use in <1.0 mol % in dichloromethane solvent effects complete reaction of the diazo ester and provides the carbenoid product in 43-88% yield. The same general method used for the preparation of Rh2(5R-MEPY)4 was employed for the synthesis of their isopropyl7 and neopentyl9 ester analogs. 

The ruthenium(ll) complex 20175c,d and the cobalt complexes 21179a and 22197b are also able to produce remarkable enantioselectivities in intermolecular cyclopropanation reactions. For the cyclopropanation of styrene with alkyl diazoacetates, the following ee-values have been reported 20 /t/V-buty , 94% (trans), 85% (cis), /-menthyl, 95% (as), 76% (trans), /-menthyl, 86% (cis), 95% (trans) 21 ethyl, 75% (cis), 20% (trans) 22 tert-butyl, 73% (trans). It is interesting to note that a catalyst analogous to 20, but with copper(II) triflate instead of ruthenium, displayed only low enantiocontrol.220b... 

Allyl methyl ether292 (ethyl diazoacetate, rhodium catalysis) and allyl tert-butyl ether124 (dimethyl diazomalonate, copper catalysis) yield cyclopropanes exclusively. With y-substituted allyl methyl ethers, C-0 insertion is generally strongly favored over cyclopropanation, even with tetraacetatodirhodium as catalyst.293 In view of these findings, the cyclopropanation of ( )- ,4-dibenzyloxybut-2-ene in moderate yield, only, to give (la,2a,3/ )-31 is notable.294... 

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