Spiro hepta-4,6-diene 1,3-cyclopentadiene

An extension of this reaction principle to other complexes related to 41 and other dienes is limited. However, 1,3-cyclopentadiene (lh) or 1,3,5,7-cyclooc-tatetraene substitute the tj6-1,3,5-cycloheptatriene ligand, and [Cr(CO)2(tj5-C5H5)(t/3-C5H7)] (5) and [Cr(CO)3(t/6-CgH8)] (72), are formed, respectively, in high yield (73). In order to prevent the formation of 5, spiro[4.2]hepta-1,3-diene and spiro [4.4] nona-1,3-diene (lu) (74) were used instead of lh. The diene lu should not readily form derivatives of t]5-cyclopentadienyl ligands. While spiro [4.2] hepta-1,3-diene does not form well-defined products, lu adds to 41 in a smooth reaction (73) [Eq. (22)]. The constitution of 43 was... 

C y clopro pan- (spiro-5 ) -bicy clo 2.2.1 ] hept-2-en-(6-spiro>-cyclopropan E17b, 1531 (Bi-cyclopropyli-den 4- Cyclopentadien) Cyclopropan-( spiro-5 ) -bicyclo [ 2.2.1 ] hept-2-cn-(7-spiro)-cyclopropan E17b, 1531 (Spiro[2.4]hepta-4,6-dien + En)... 

Cyclopentadien-<5-spiro-7>-bicyc-lo[4.1.0 hepta-2,4-dien Tetra-chlor- -trifluormethyl- E19b, 809 (Carben + Aren)... 

The method described here is the direct adaptation of the original procedure developed by the late Professor Hans Schmid- As summarized in Scheme 1, the Schmid reaction has been successfully applied to [4 + 3] cycloadditions with cyclopentadiene, spiro[2.4]hepta-4,6-diene, and N-Boc-pyrrole. Additional examples can be found in references 8 and 9. Use of functionalized six-membered oxyallyls and synthetic applications of the [4 + 3] cycloadducts have also been described.8... 

The Diels-Alder reaction of methylenecyclopropane with cyclohexa-1,3-diene at 120°C gave the spirocyclopropanebicyclooctene in 50% yield.When cyclopentadiene and spiro[2.4]hepta-4,6-diene were used as dienes the respective spirocyclopropanenorbornenes were obtained. At 190°C, (chloromethylene)cyclopropane underwent [2 + 4] cycloaddition reactions with cyclopentadiene, furan and cyclohexa-1,3-diene to give the respective Diels-Alder adducts. The reaction of buta-1,3-diene and cyclohexa-1,3-diene with bicyclopropylidene as dienophile gave predominantly the [2 + 2] cycloadduct in addition to a small quantity of the Diels-Alder product. Cyclopentadiene, however, formed exclusively the dispirocyclo-propanenorbomene as result of a formal [2 + 4] cycloaddition. 

An example of the reduction of a nonactivated cyclopropane by lithium in liquid ammonia is the reduction of 1-methyl- and l,l-dimethylspiro[2.4]hepta-4,6-diene. Either cyclopropane bond at the spiro center was cleaved to give alkyl-substituted cyclopentadienes 1 and 2. ... 

Ring closure also occurs on reaction of cyclopentadiene with ethylene dibromide and sodium in liquid ammonia, the product being spiro[2.4]-hepta-4,6-diene (75% yield) 387... 

Lanthanide /3-diketonates have been used as catalysts in Diels-Alder reactions. The first example of a lanthanide-catalyzed cycloaddition was the dimerization of spiro[2.4]hepta-4,6-diene by [Eu(tfn)3] (Morrill et al., 1975) (scheme 2). In the absence of the europiitm(lll) complex no dimerization took place. Because of the mild experimental conditions, this catalyst has potential in Diels-Alder reactions where acid labile components are combined. An example is the cycloaddition of cyclopentadiene with acrolein (Danishefsky and Bednarski, 1985). 

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