Spiro -hepta-4,6-diene

FIGURE 11. Comparison of the PE spectra of (a) fulvene 175 and (b) homofulvene (spiro[2.4]hepta-4,6-diene) 74... 

Scheme 6.53 Products formed by cycloadditions of 3<52-l H-naphthalene (221), liberated from 220 by KOtBu, with furan, 2,5-dimethylfuran and spiro[2.4]hepta-4,6-diene.

Whereas alkylation of activated methylene systems by classical methods produces a mixture of mono- and dialkylated products, with the latter frequently predominating, phase-transfer catalytic procedures permit better control and it is possible to obtain only the monoalkylated derivatives. Extended reaction times or more vigorous conditions with an excess of the alkylating agent lead to dialkylated products or, with dihaloalkanes, carbocyclic compounds as the technique mimics dilute concentration conditions, e.g. the resonance stabilized cyclopentadienyl anion, generated under solidiliquid two-phase conditions, or under liquiddiquid conditions, reacts with 1,2-dihaloethanes to form spiro[2,4]hepta-4,6-diene (70-85%) [1-3]. Reaction with dichloromethane produces bis(cyclopenta-2,4-dien-l-yl)methane (60%) [4],... 

Although the gem-dihalocyclopropanes are fairly stable compounds, they can participate — as has been shown in the above sections — in quite a number of chemical transformations. Several reactions between dihalocarbenes and alkenes have been described in which no dihalocyclopropane formation could be observed that these intermediates might have been produced was only inferred from the type of products finally isolated. A typical process of this type is the e/ufo-addition of dihalocarbenes to norbomene and norbomadiene as discussed above. Comparable rearrangements have been observed, when dichlorocarbene additions either lead to aromatic products or when they cycloadd to rather inert aromatic systems. In the latter case a ring-enlargement takes place. A reaction related to the concerted opening of two cyclopropane rings in a bicyclopropyl system as discussed above takes place when dichlorocarbene is added to spiro[2.4]hepta-4,6-diene [227]. 

Initial thermal sigmatropic 1,5-carbon shifts are believed to account for the product formation from spiro[2.4]hepta-4,6-diene (l) 200 and spiro[cyclopropyl-l, 2 -2 //-indene] (6),201 obtained by photodecarbonylation of dione 5. In the first case, a 1,5-hydrogen shift and an electrocyclic ring opening completes the formation of 3,4-dimethylenecyclopent-l-ene (4),200 and in the second case, the initially formed benzoannulated bicyclo[3.2.0]hepta-l,3-diene 7 dimerizes to 8 as mixture of two stereoisomers.201... 

Other syntheses of the spiro[3.3]hepta-l,5-diene system by Cope elimination. Norrish type II reaction and dehydrobromination, respectively, are shown below.ig... 

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... 

Propanol l-Chlor-3-(4-methyl-phenyl)- Vl/la, 2, 1263 Spiro[2.4 hepta-4,6-dien l -Chlor-2,2-dimethyl-l-methoxy- E19b, 1660 (Carben + En)... 

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)... 

Penten-l-in 5-Cyclohexyl-V/ld, 669 Propan 2,2-Dimethyl-l-phenyl-V/la, 479, 492, 496 Spiro 2,4 hepta-4,6-dien, 1,2-Diethyl-E19b, 797 (Carben + En) Tetracyclo 4.2.0.02,8.04, octan 1.5,5-Trimethyl- E19b, 438 (a-Eliminierung//Mnsertion) Tetracyclo[3.2.1.02-7.03,6 octan ... 

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

Similarly, with spiro[4.4]nona-1,3-diene and spiro[2.4]hepta-4,6-diene, Fe(CO)5 produces the 7r-cyclopentadienyl-type binuclear complexes (248, reference 3), while Fe2(CO)fl affords the tt complexes (90) and (91), respectively. With the latter olefin, the complex of structure... 

Steric and electronic factors in the reductive cleavage of methyl-substituted phenyl cyclopropanes (145) and in spiro[2.4]hepta-4,6-dienes like 146 have been investigated by Staley and Rocchio. ... 

Among the known [4 + 3] cycloaddition protocols examined, only the Schmid2 and Fohlisch4-10 procedures were found to afford the [4 + 3] cycloadducts in synthetically useful yields. Schmid s rarely-used "aminoallyi" reaction appears to be most effective, particularly when sterically demanding 1,3-dienes [e.g., spiro[2.4]hepta-4,6-diene] or otherwise recalcitrant N-acylpyrroles are required for the cycloadditions. On the other hand, with sterically unencumbered 1,3-dienes and also with furans, the Fohlisch reaction has emerged as the method of choice in view of the practical aspects of simple and convenient execution. 

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 reaction of epoxyfulvene 3 with nucleophiles Nu to give spiro[4.2]hepta-l,3-diene derivatives 4 is closely related. ... 

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