Cyclopentadiene 5-diazo

Cyclopentadien 5-Diazo-l,2,3,4-tetrakis-[trifluormethyl]- E14b, 970 (Cyclopentadienid + NO/KN02)... 

Cyclopentadien Diazo-tetrabrom-X/4,600 (alle H -> Br) E14b, 1139 (Hydrazon -+ N2)... 

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. 

Enol ether additives were used to probe the protonation of 3-cyclopen-tenylidene (127). Treatment of A-nitroso-A-(2-vinylcyclopropyl)urea (124) with sodium methoxide generates 2-vinylcyclopropylidene (126) by way of the labile diazo compound 125 (Scheme 25). For simplicity, products derived directly from 126 (allene, ether, cycloadduct) are not shown in Scheme 25. The Skat-tebpl rearrangement of 126 generates 127 whose protonation leads to the 3-cyclopentenyl cation (128). In the presence of methanol, cyclopentadiene (130) and 3-methoxycyclopentene (132) were obtained.53 With an equimolar mixture of methyl vinyl ether and methanol, cycloaddition of 127 (—> 131)... 

Compounds containing a CH2 bonded to two Z groups (as defined on p. 464) can be converted to diazo compounds on treatment with tosyl azide in the presence of a base,164 The use of phase transfer catalysis increases the convenience of the method.165 p-Dodecylbenzenesul-fonyl azide,166 methanesulfonyl azide,167 and p-acetamidobenzenesulfonyl azide168 also give the reaction. The reaction, which is called the diazo transfer reaction, can also be applied to other reactive positions, e.g., the 5 position of cyclopentadiene.169 The mechanism is probably as follows ... 

Ramirez Levy (Ref 3) advise extreme caution during all operations with Diazo-cyclopentadiene, since during one prepn, they reported, a violent expln took place after distillation... 

Cycloaddition reactions can also lead to the formation of pseudoazulene lattices, for example, the reaction of acetylene dicarboxylates with diazo-cyclopentadienes cyclopenta[c]pyradizines (55).140 142... 

In contrast to diazenes, the electronic structure of diazocompounds was not so intensively studied. The HOMO of diazomethane was calculated to be a bi(n) orbital corresponding to the non-bonding orbital of a tr-allyl system22 26-28 (Fig. 2). This orbital is responsible for the 1.3-dipolar reactivity of diazoalkanes. Typical ionisation energies are 9.0, 7.88 and 8.33 eV for diazomethane, 2-diazopropane and diazo-cyclopentadiene, respectively28. ... 

Caution. Diazo compounds are potentially explosive. Although neat 5-diazo-l,3-cyclopentadiene is known to be highly explosive,6 it may be handled conveniently and safely in a pentane solution.2,1 Tetrachloro-5-diazo-l,3-cyclopentadiene is reported to be stable, but due caution should be exercised in the manipulation of this compound. Carbon monoxide, volatile metal carbonyls, and some diazo compounds are highly toxic, and reactions with these species should be conducted in a well-ventilated fume hood. Avoid inhalation or contact with skin. 

Caution. Tetrachloro-5-diazo-l,3-cyclopentadiene, Cs CUN2, is said to be very stable8 and we exerienced no difficulty. However, it is advisable to use care when subjecting the compound to extreme reaction conditions. 

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 formation of 1,3-dienes within a cyclic framework has been accomplished via extrusiem of molecular nitrogen. Cyclobutadiene has been obtained by nitrogen extrusion from 2,3-diazo-Dewar benzene, which is generated by mild oxidation of 2,3-dioxybicyclo[2.2.0]hex-S-ene. Other cyclic dienes that have been similarly obtained are cyclopentadiene and cyclohexa-1,3-diene from the corresponding diazo compounds. 

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. ... 

In contrast to the high dipolarophilic reactivity toward diazo compounds, the P=C bond of 1,2-thiaphospholes does not act as a dienophile toward cyclopentadiene. No reaction of 3,5-diphenyl-l,2-thiaphosphole with cyclopentadiene was observed at 20-80 °C. However, heating this thiaphosphole with a large excess of cyclopentadiene at 120 °C in a sealed tube produced a mixture of the polycycles 21 and 22, which represent the formal 4 1 and 3 1 cycloadducts with cyclopentadiene (Scheme 9) <2003EJ01894>. 

---