Cyclopentadienes, diazo preparation

Our retrosynthesis of (—)-kinamycin F (6) is shown in Scheme 3.20 [45]. It was envisioned that (—)-kinamycin F (6) could be prepared from the protected diazofluorene 114 by conversion of the ketone function of 114 to a trans-], 2-diol, followed by deprotection of the acetonide and methoxymethyl ether protecting groups. The diazofluorene 114 was envisioned to arise from diazo transfer to the hydroxyfulvene 115. The cyclopentadiene substructure of 115 was deconstructed by a two-step annulation sequence, to provide the bromoquinone 116 and the p-trimethylsilylmethyl unsaturated ketone 117. The latter two intermediates were prepared from juglone (118) and the silyl ether 119, respectively. 

Cyclopentadimylidene (2). 2 was very easily obtained by photolysis or thermolysis of the corresponding diazo-cyclopentadienes (72). These were prepared by straightforward procedures (diazo-group transfer, dehydrogenation of hydrazones, or Bamford-Stevens reaction of tosyl-hydrazones) 26-80) from either cyclopentadienes (77) or substituted cyclopentadienones (73). 

The transformation of an active CH compound into the corresponding diazo derivative with -toluenesulfonyl azide has been designated a diazo transfer reaction and possesses a variety of preparative uses. The method has been useful for the syntheses of diazo derivatives of cyclopentadiene, 1,3-dicar-bonyl compounds, 1,3-disulfonyl compounds,1,3-keto-sulfonyl compounds, ketones, " carboxylic acid esters, and /3-keto imines. Further reaction of these diazo intermediates can lead to azo compounds,"- " 1,2,3-triazoles, and pyrazolinones. ... 

Two other methods which have been widely used for the preparation of cyclopentadienylides involve the carbenic decomposition of diazo-cyclopentadiene in the presence of a suitable carbene acceptor, and the condensation of cyclopentadienes with sulphoxides or arsine oxides, e.g. 

A simple and efficient method for the preparation of a-diazo- i-hydroxy esters by the condensation of aldehydes with ethyl diazoacetate using chloromethy-lated polystyrene SIL as a heterogeneous catalyst in water was developed [66]. Moderate to excellent yields of the corresponding a-diazo-jl-hydroxy esters were obtained. The catalyst was separated by filtration and reused in five consecutive cycles without any appreciable loss of activity. Later MacMillan s imidazolidinone was noncovalently immobihzed in the pores of siHca gel with the aid of IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (Mac-SILC) (SILC, supported ionic liquid catalyst) [67]. The Mac-SILC as an SIL catalyst was utilized for the enantioselective Diels-Alder reaction of cyclopentadiene and cinnamaldehyde. The Mac-SILC was more active, especially to an electron-rich dienophile, than its homogeneous counterparts, and the reaction could proceed under mild conditions. 

---