IN our detailed study of photochsmical behavior of simple acyclic a.rpdnsaturated ketones (I), us have observad three differsnt kinds of behavior of these ketones upon irradiation. One, tbs formation of cyclopropane derivatives when the carbon rtom y to the carbonyl group is a quarternary one (Ia, R=kbut.yl, R1=Rv=& Ib, R+butPl, R'=T, R"=H) hs been reported (2).
Other structurally similar ketones were found to undergo facile isomerization to the g,y-unsaturated Isomers, or were characterized by their unusual reslstance to any photochemical change upon irradiation. Lack of reactivity was typical for simple homologs of I, 3-penten-e-one (Ic, RCH3, R'=R"=H), mesityl oxide (Id, R=Rt=CH3, RQB) and 3&dimetbyl->penten-2-one (IO, R= R'=Rv=CIi$ undcu a large variety of conditions. We have also observed this resistancs in 4,5-dimethyl-3_hazen-2-one (If, R=CH(CR$,, R'=C%, R"=K) (3).
The lack of reactivity in this caze was particularly surprising as its relative, 5-methyl-3_hexen-2-one (Ig, R=CH(C%)2, R*=Rn=H)r was found to undergo 4 f8cile isomerization to tbe &y-lsomert 5-methyl-kbeuen-2-one (II) in very
(1) Fbllov of the Alfred P. Sloan Foundation.
(2) Me J. Jorgenson and II. C. Yang, J. Am. Chem. Sot., 5, 1698 (1963).
(3) The cis-trans pbotostationary state (cis:trans, 95:s) of If was X'Udw established. Upon prolongad irradiation a slow change to polymeric products took place.