Spiro heptadiene

Diisobutylaluminium hydride catalyses the ring-closure of various dienes. It is proposed that the process involves addition of the aluminium hydride to a terminal double bond, followed by ring-closure and, finally, elimination of the catalyst (equation 106). Thus 1,5-hexadiene gives methylenecyclopentane (213) (equation 107), 1,6-heptadiene gives methylenecyclohexane (214) (equation 108), 4-vinylcyclohexene gives bicyclo[3.2.1]oct-2-ene (215) (equation 109) and the spiro compound 217 is obtained from 5-methylene-l,8-nonadiene (216) (equation 110)112. 

The mechanism of the cycloaddition appears to be concerted for various reagents however, for several cases, radical cation cycloaddition-cycloreversions have a stepwise component. For example, CIDNP effects observed during the PET induced dimerization of spiro[2.4]heptadiene (97) identify a dimer radical cation with spin density only on two carbons of the dienophile fragment this intermediate must be a doubly linked radical cation ( 99 + 282,283 pulsed laser experiment at high concentrations of 97 supports a second dimer radical cation at high... 

Diels-Alder cycloadditions of the readily available spiro[2.4]heptadiene (15) are a useful entry to spiro(cyclopropane-l,7 -norbornene) and related polycyclic compounds (equation 17)38. 1,1 -Diacetylcyclopropane was found to undergo unusual base catalyzed cyclizations resulting in spiroannulated cyclopropanes (equation 18)3,-4°. 

However, only limited experimental evidence is available concerning the key step of the dimerization, i,e. the addition of the radical cation to the parent olefin. Does this addition occur stepwise or in concerted fashion Does the radical cation serve as a the diene component ([3 + 2]cycloaddition) or as dienophile ([4+ l]cy-cloaddition) The observed retention of dienophile stereochemistry and orbital symmetry arguments (Fig. 7) favor the [4 + l]cycloaddition type. Although it is difficult to distinguish the [3 + 2] from the [4 + l]addition type, a stepwise component for the cycloaddition and the complementary cycloreversion has been established in at least one system, viz., spiro[2.4]heptadiene. 

For two attached unsaturated groups as in spiro[2.4]heptadiene and 1,1 -diethynylcyclopropane, a stronger interaction causes significant shortening of the distal bond. Boese, R. Haumann, Th. Kozhushkov, S.I. de Meijere, A. (unpublished results). 

Furukawa-Simmons-Smith-Reakt.), 848 f. (Sawada-Sim-mons-Smith-Reakt.) E17a, 362f. (Ar—CH = M 4- En), 932 (3-C1 —2-Ar—propen/R2BH 4-OH-) E17b, 1279 (1-S02-Ar - 1-H) E18, 832 (En 4- Carben) E19b, 204/206 (En 4- Carben) Cyclopropan-[Pg.607]

Roth and coworkers obtained CIDNP evidence for a singly bonded intermediate in the radical cation Diels-Alder dimerization of spiro[2,4]heptadiene [107]. Gassman and Singleton pointed out that acid-catalyzed (4 - - 2) addition reactions can compete with the radical cation chain process when a hindered base (2,6-di-tert-butylpyridine) is not included. For 2,4-dimethyl-l,3-pentadiene (89 of Scheme 19)... 

Addition of dibromomethyllithium (generated from dibromomethane and lithium diiso-propylamide) to fulvenes, and cyclization of the dibromolithium intermediates 2 is an efficient route for the preparation of spiro[2.4]heptadienes 3. ... 

Cyclopropan-(spiro-l 1 )-dibenzo-l, 4-dipho pha-bicyclo[2.2.1]heptadiene... 

Cyclopropan-<3-spiro-12>--l,3-dioxan-octadien--tricyclo 2.2.1.0. 0 beptane... 

Bicyclo(2.2.1 hepfadien-(7-spiro-3)- ,4-dioxan- 2-spiro-7)-bicyclo 2.2. l heptadiene 2205... 

Bicyclo(2.2.l]heptadien-<7-spiro-3)-azetane-< 2-spiro-7>-bicyclo 2.2.1 Iheptadiene... 

Spiro[2.4]heptadiene rearranges to 6-methylfulvene and 5-vinylcyclopentadiene in a 5 4 ratio, respectively, with log k = 12.89 — 43 600/23RT Subsequently, it was shown that interconversion of cis- and 1,2-dimethyl derivatives preceded the structural isomerization." The structural and geometric isomerizations would appear to involve cleavage to a biradical followed by hydrogen shift or reclosure after bond rotation (Scheme 8.23). 

The cleavage of the three-membered ring in bicyclo[2,l,0]pentanes and spiro-[4,2]heptadienes can be effected by metal carbonyls, and with the latter organic substrates carbonyl insertion reactions are observed. 

The structure of spiro[2.4]heptadiene (1) has been accurately determined by microwave spjectroscopy. Use an orbital mixing diagram to rationalize the structural differences between 1 and the model compounds cyclopropane and cyclo-pentadiene. Include sketches of all relevant orbitals. (Numbers shown are bond lengths in A.)... 

Both [1,5]-alkyl and hydrogen shifts take place in the thermal conversion of the spiro-dienes, 6,9-dimethylspiro-[4,4]-nona-l,3-diene 25 to 26 and of spiro-[4.2]-heptadiene 27 to 28 [15]. 

In contrast to furan, the exo-diastereoselectivity of the product oxetane in the photocycloaddition of spiro [4.2]-heptadiene 126 to benzaldehyde was reduced substantially to an exo/endo-r tio of 3.5 1 by the spiro-cyclopropane ring. The opposite exclusive endo-diastereoselectivity was found in the reaction with methyl ester of phenyl pymvate 127. Possibly emio-orientation of the large carbomethoxy... 

Employing this protocol, spirocyclopentanones can be obtained when cyclic ketones are used, as illustrated in Scheme 31.The spirocyclopentanone 129, obtained from 4-methylcyclohexanone 126, has been converted to the spiro ketone 130, which was earlier transformed to the sesquiterpene a-cedrene 131 (Scheme 31). Thus, CuOTf catalyzed photocycloaddition of 1,6-heptadienes provides a novel route to spiro cyclopentanones, also. 

Solvent influence on isomer ratio, nitration 16, 411 Solvents, polar (s. a. Nitrobenzene) 16, 933 Sommeiet reaction 16, 818 Spiro[4,2]-l,3-heptadienes 16, 865... 

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