Photochemical Syntheses: I. The Reaction of Aldehydes and Ketones With Cycloalkenes

Abstract

The irradiation of dialkyl ketones in cyclohexene leads to the formation of cyclohexenyldialkylcarbinols. The use of aldehydes leads to the formation of the corresponding secondary alcohols, but the reaction is more complex because of concomitant Kharasch addition which can, however, be suppressed. The mechanism of the alcohol formation has been elucidated by the use of an optically active substrate, carvomenthene, and has been shown t o involve the intermediacy of a tyclohexenyl radical. The structure and genesis of a biscarbinol by-product is discussed.I t was first observed by Bowen and Horton (I) that the irradiation of acetone in cyclohexane gave, in poor yield, an alcohol which was presumed to be cyclohexyldimethylcarbinol. More recent investigations (2) confirmed this, but the yield (12y0) was not such as to render the reaction preparatively a very useful one.I t seemed probable that if the reaction proceeded by initial hydrogen atom abstraction by the photoactivated carbonyl compound, then ally functio~lal group designed to stabilize that radical should render the reaction more facile; and indeed there were indications in the literature (see, for instance, refs. 3 , 4 , 5 ) that in related transformations this was so.A simple function that would fulfill the requirements was the ethylenic linkage and to this end the symmetrical hydrocarbon cyclohexene was selected. Irradiation a t roo111 temperature of a solution of acetone in this hydrocarbo~i until no carbonyl band could be detected in the infrared gave, after removal of excess hydrocarbon and distillation from a polymeric residue, a colorless oil. This could be separated by gas-liquid chromatography into an alcohol, shown to be the desired carbinol, and 3,3'-bicyclohexenyl. The latter was characterized as the known two tetrabromides (6).'The alcohol showed bands in the infrared a t 3322 (hydroxyl), 1378 and 1368 (geminal dimethyl), and 733 cm-I (cis disubstituted ethylene) in accordance with structure (I, I< = R' = Me), and had the required analysis. I t was characterized a s the 3,5-dinitrobenzoate, and a n authentic specimen of the alcohol was synthesized from cyclohexene-3-carboxylic acid by esterification (diazomethane) and Grignard reaction with methyl magnesium iodide. The alcohol so obtained and the derived 3,s-dinitrobenzoate were identical in every respect with the corresponding photoproducts.Under similar conditions the carbinols (I, R = R' = E t ) and (I, R = R' = Pr) were obtained employing diethyl and dipropyl ketone respectively.When the cyclol~exene-acetone irradiation was performed a t reflux temperature there was isolated in poor yield an additional substance, a saturated alcohol, which was readily characterized as a crystalline 3,5-dinitrobenzoate. The analysis indicated the condensation of two molecules of acetone with one of cyclohexene. The absence of unsaturation suggested structure (11) and comparison with an authentic specimen (see Experimental) confirmed this.'illa?zuscript received ivovember 8, 1960. Contribt~fion fr...

Photochemical Syntheses: 6. The Formation of Heptandiones From Acetylacetone and Alkenes

“…The formation of cyclobutane derivatives by the dimerization of unsaturated ketones is well known (1.5) and the intramolecular addition of an ethylenic linkage to an unsaturated ketone has already been observed (16). 5 The present reaction constitutes the first intermolecular addition to an isolated ethylenic linkage. In support of this view the infrared spectrum of the crude irradiation product showed strong hydroxyl absorption which disappeared on slight warming.…”

Some Chemistry of Heteratisine

“…A recent note outlines the determination of its structure by X-ray crystallography3 (1). Simultaneous with this determination a number-of simple transformation products of the alkaloid were prepared.…”

The Beckmann Rearrangement and Fragmentation of Substituted Bicyclo[2.2.2]octan-2-one Oximes1

“…The greater substituent effect was observed "in the case of phenyl in the 1-position. Thus, rearrangement of 4methoxy-l-phenylbicyclo [2.2.2 ]octan-2-one oxime (4) afforded only nitrile 14 in 77% yield. These results are compatible with an assumption12 that the ratio of lactam formation to fragmentation decreases with the stability of the carbonium ion formed by cleavage.…”