Solvolytic studies of tricyclo[4.2.0.02,4]octan-5-yl derivatives. Effect of cyclopropane and cyclobutane orbital alignments on reactivity and proclivity for rearrangement

Abstract

The kinetics of hydrolysis of the four possible stereoisomeric tricyclo[4.2.0.01 2' 4]octan-5-yl 3,5-dinitrobenzoates and p-nitrobenzoates in 80 % aqueous alcohol have been studied at several temperatures. A striking feature of the present results is the convergence of both pairs of isomers to two related but noninterconverting cations (51 and 52), only the latter of which is capable of cyclobutane ring opening or ring expansion for stereoelectronic reasons.Both 1 a,2j3,4/3,6a-dinitrobenzoates gave identical product mixtures (after 10 half-lives) consisting of exo-cisbicyclo[4.2.0]oct-2-en-5-ol (21a) and its internally returned ester 21b. Ionization in the la,2a,4a,6a series led to formation of the epimeric m-bicy clo[3.3,0]oct-2-en-6-ols (26 and 27, 52-58%), e/itfo-rá-bicyclo[4.2.0]oct-2-en-5-ol (28, 33-41%), and the alcohols of retained tricyclic structure (17 and 20, 7-9%). The formation of the [4.2.0] bicyclic alcohols with hydroxyl orientation inextricably linked to a specific precursor geometry implicates a rigid cation geometry and highly directed discharge by solvent. Studies of the products obtained from hydrolysis of deuterium labeled ester 42 showed the absence of deuterium scrambling and excluded the operation of cyclopropylcarbinyl-cyclopropylcarbinyl rearrangement. Carbocationic leakage of the homoallylic -> allylic type was also not in evidence. A connection is drawn between various [3.1.0] bicyclic systems and the reactivity features of these molecules are discussed. Further consideration is given the general questions of bisected bishomoallylic cation intervention and of cyclobutane neighboring group involvement.

Carbon-13 chemical shifts in bicyclo[3.3.0]octanes

“…The cooling bath was removed, and the reaction mixture was allowed to reach room temperature, where it was stirred for 1 h. Partitioning between ether and aqueous hydrochloric acid gave, upon concentration of the organic layer, 0.428 g of the methyl ketone, pure by 13C and gas chromatography: NMR (CDCI3) 1.15 (d, 3 ), 1.4-2.9 (m, 11 H). exo-2-Methyl-c/s-bicyclo[3.3.0]octane (10). To a flask containing 4.5 cm3 of triethylene glycol, 0.45 cm3 of hydrazine (95%), and 0.56 g of potassium hydroxide was added 0.43 g (3.1 mmol) of methyl ketone 49. this mixture was slowly heated, with stirring, until the oil bath reached 180 °C.…”

“…For these reasons, we chose to investigate exo-and endo-8-carbenatricyclo(3.2.1.02~4]~ctane (13 and 28).Decomposition of the tosylhydrazone of exo-8-tricyclo[3.2.1.02~4]octan0ne (9) in bis(2-ethoxyethyl) ether (3.3 equiv of NaOCH3) at 160 "C gives a 20% yield of hydrocarbons, composed of 65% of bicyclo[3.3.0]octa-l,6-diene(10) and The simplicity of 3-carbenabicyclo[3.1.0]hexane (4) was appealing initially; however, the methoxide ion induced decomposition of the tosylhydrazoneof 3-bicyclo[3.l.0]hexanone (6) generates bicyclo[3.1.0]hexene-2 (8) in 91% yield, most probably as a result of 1,2-hydrogen migration of 3-carbenabicyclo[3.1.0]hexane.10 Thus, any trishomocyclopropenyl character which might actually be present in 3-carbenabicyclo[3.l.0]hexane is not revealed.…”

Nature-inspired catalytic asymmetric rearrangement of cyclopropylcarbinyl cation

“…Cyclopropylcarbinyl cation (1)(2)(3), an important reaction intermediate, has aroused widespread interest and controversy regarding its classical or nonclassical cationic nature (4)(5)(6), which centers primarily on questions of the structural geometry and electron delocalization. In 1951, Roberts (1) first proposed a nonclassical tricyclobutonium ion for explaining the observation that the deamination of cyclopropylcarbinyl amine with nitrous acid produced a mixture of cyclopropylcarbinyl, cyclobutyl, and homoallyl alcohols (Fig.…”