Synthesis of [1.1.1]Propellanes by Cyclization of 3-Alkylidenecyclobutylidenes
摘要:
Starting from tricyclo[3.1.0.0(2,6)]hexane 5 and 1-bromobicyclo[1.1.0 ]butane 6, a series of [1.1.1]propellanes 15 and 21 has been synthesized which carry alkyl, aryl, alkenyl, and alkynyl groups. Propellane formation proceeded via 1-bromo-1-chloro-3-alkylidenecyclobutanes of type 13 and 19, which on treatment with methyllithium gave rise to the generation of carbenes 14 and 20 as short-lived intermediates. For these carbenes, the most efficient path of stabilization is obviously the intramolecular cycloaddition. Ab initio MO calculations at the Becke3LYP/6-31G* and MP2/6-31G* level of theory indicated that 3-alkylidenecyclobutylidenes 4 and 37a-d are not local energy minima but collapse to the corresponding [1.1.1]propellanes. On this basis, propellane formation should follow a carbenoid reaction path.
1,6-Dibromotricyclo[3.1.0.02,6]hexane 2e has been prepared in 56% yield by reaction of 1,6-dilithiotricyclo[3.1.0.02,6]hexane 2d with 2.5 equiv. of tosyl bromide. 2e proved to be a new source for generating tricyclo[3.1.0.02,6]hex-1-(6)-ene 1 by reaction with magnesium, with lithium sand, or with tert-butyllithium, as shown by formation of the Diels-Alder adduct 5. Ene adducts of 1 were obtained with
Central and lateral bicyclo[1.1.0]butane bond cleavage with subsequent Wagner-Meerwein rearrangements or carbene formation in the 185-nm photolysis of tricyclo[3.1.0.02,6]hexane, tricyclo[4.1.0.02,7]heptane, and tricyclo[5.1.0.02,8]octane
From the deuterium-labeling studies, it is concluded that, in the case of the tricyclooctane, the central bicyclobutane bonds cleave in the primary step to give radical cationic or zwitterionic species that undergo a Wagner-Meerwein rearrangement. Also, in the case of tricycloheptane, this is the dominating pathway but lateral C-C bond cleavage with subsequent carbene and product formation takes place
从氘标记研究得出的结论是,在三环辛烷的情况下,中心双环丁烷键在初级步骤中裂解,产生自由基阳离子或两性离子物质,这些物质经历 Wagner-Meerwein 重排。此外,在三环庚烷的情况下,这是主要途径,但横向 CC 键断裂以及随后的卡宾和产物形成发生在大约 10 倍的范围内。15%。对于三环己烷,该途径成为主要途径。我们的光机械观察与早期关于双环丁烷 HOMO 的相对能量排序的理论研究非常一致,因为产品组成反映了这一点
Hashmi, A. Stephen K.; Szeimies, Guenter, Chemische Berichte, 1994, vol. 127, # 6, p. 1075 - 1090