Synthesis and Dimerization of Bicyclo [4.4.1] undec‐1 (11)‐ene, a Bridged trans‐Cycloheptene

Abstract

The synthesis of bicyclo[4.4.l]undec-1(ll)-ene (5) by intr,amolecular Wittig reaction is described. The Bredt olefin could not be isolated, but dimerized rapidly to a novel compound 15 containing a cyclopropane ring. The olefin 5 was trapped in situ by 2,5-diphenylbenzo [clfuran.Introduction. -The question of the limits of Bredt's rule is of considerable current interest [l] [2]. It is now generally accepted that the strain of a bicyclic or polycyclic bridgehead olefin (Bredt olefin) is comparable to the strain of the corresponding trans-cycloalkene from which it may be formally derived by bridging. This hypothesis, advocated by Wiseman in 1967 [3], has been supported by experimental evidence from a large number of synthetic approaches to different Bredt olefins and by two independent force-field calculations [4] [S].However, within a series of homologous bridged trans-cyclooctenes, truns-cycloheptenes, and trans-cyclohexenes, the principles which govern relative strain energies are not obvious. Kobrich [l] formulated a rule ('rule A'), according to which increasing the number of carbon atoms in the bridge should decrease the strain of the Bredt olefins. Indeed, whereas the ethylene-bridged truns-cyclo-

ChemInform Abstract: SYNTHESIS OF 1‐BICYCLO(3.2.2)NONENE AND 1(7)‐BICYCLO(3.2.2)NONENE BY INTRAMOLECULAR WITTIG REACTION

“…(a-Cycloheptene has been prepared and trapped in situ, but could not be isolated [5]. Several bridgehead olefins related to (E)-cycloheptene are known: 1 (1 1)-Bicyclo [4.4.l]undecene (l), formally a tetramethylene-bridged (E)-cycloheptene [6], the ethylene-bridged 1-bicyclo 13.2.21nonene (2) and 1 (7)-bicyclo-[3.2.2]nonene (3; prepared as a mixture [7]), and 6,9-dichloro-l(9), 3-bicyclo[4.2.1]nonadiene (4) [8], the methylene-bridged l-bicyclo[3.2.l]octene (5) [9], 1 (7)-bicyclo[3.2.l]octene (6) [lo], and 4-methyl-l,3-bicyclo[3.2.l]octadiene (7) [ll], and the tricyclic bridgehead olefins homoadamant-3-ene (3-tricyclo (a-Cycloheptene isomerizes to (a-cycloheptene. Because such an isomerization reaction is not feasible in bridgehead olefins, one would expect that bridged (a-cycloheptenes are kinetically more stable than the reference compound.…”

“…The dimers obtained usually are cyclobutanes formed by a formal [2 + 21 cycloaddition (see e.g. 181 [12]), but notable exceptions are an 'ene' dimer from 9 [13], and a 'homo-ene' dimer from 1 [6].…”

Synthesis of β-, γ-, δ-, ..., ω-Halogenated Ketones and Aldehydes

“…Hence, alcohols are often activated toward nucleophilic substitutions by converting them into mesylates (Scheme ) . In a typical procedure, the alcohol is treated with mesyl chloride 55 in dry CH 2 Cl 2 , , in the presence of a base such as Et 3 N, at room temperature or below. This transformation usually proceeds in very high yield, if not quantitative.…”

“…This transformation usually proceeds in very high yield, if not quantitative. Subsequently, the mesylate 1143 is treated with LiCl or LiBr in warm acetone to furnish the respective alkyl halide 1144 . ,, In some cases, the halogenation step is performed in the presence of the sodium salt of the halide , or in another polar aprotic solvent such as DMF . The example presented in Scheme illustrates the possible occurrence of acetal hydrolysis under the conditions used to substitute the mesylate for a halide.…”

The Intramolecular Ramberg‐Bäcklund Reaction: A Convenient Method for the Synthesis of Strained Bridgehead Olefins

“…See [21]. cis-I-Thiadecalin-I,I-dioxide (21). To a solution of cis-I-thiadecalin (19) [22] (1.51 g, 9.6 mmol) in dry ether under N2 at OD, a solution of m-chloroperbenzoic acid (4.2 g, 21.7 mmol) in ether was added dropwise.…”