Hydrazine lactone group reaction with

Reaction of the Lactone Group with Hydrazine and Derivatives... 

Eschenmoser s pyrone 38 on treatment with cyclopropenone ketal 39 in refluxing benzene afforded lactone 40 (73%). Lactone 40 on hydrolysis with acetic acid at 100°C afforded, after deprotection and decarboxylation, tropone 37 (70%). Introduction of the tropolonic hydroxyl group was achieved with hydrazine hydrate in ethanol, to give a mixture of deacetyl-colchiceinamides 41 (53%) and 42 (37%), followed by reaction with ethano-lic potassium hydroxide, which afforded tropolones 43 and 44, respectively. Tropolone 43 was converted to 44 which, therefore, became the major reaction product. Methylation of 44 gave a mixture of enol ether 18 and 45 which were separated by chromatography. 

Diastereoselectivity is also observed in reactions of carbanions derived from imines and hydrazones, when those species contain a chiral center or a chiral auxiliary (sec. 9.4.F). Asymmetric imines can be used, and chiral oxazoline derivatives have also been prepared and used in the alkylation sequence (sec. 9.3.A). Meyers showed that chiral oxazoline 478 could be alkylated to give the ethyl derivative, 479. A second alkylation generated the diastereomeric product 480, and hydrolysis provided the chiral lactone (481) in 58% yield and with a selectivity of 70% ee for the (R) enantiomer. 53 As pointed out in Section 9.4.F.ii, hydrazone carbanions can be used for alkylation or condensation reactions. In a synthesis of laurencin. Holmes -l prepared the asymmetric hydrazone 483 (prepared by Enders by reaction of cycloheptanone and the chiral hydrazine derivative called SAMP, 482-A-amino-(2S)-(methoxymethyl)pyrrolidine)- - and showed that treatment with LDA and reaction with iodomethane gave an 87% yield of the 2-ethyl derivative in >96% de. Ozonolysis cleaved the SAMP group to give (/ )-2-ethylcycloheptane (484) in 69% yield. The enantiomer of 482 is also known (it is called RAMP, A-amino-(27 )-(methoxymethyl)pyrrolidine). 

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