HERBERT 0. HOUSEAND RICHARD L. WASSON
1488
[CONTRIBUTION FROM THE
DEPARTMENT O F CHEMISTR?r, hlASSACIICSETlS
Vol. 79
I N S T I I U I h OP ' J ? h C I I N O L 0 4 1 ]
The Rearrangement of a,P-Epoxy Ketones. V. Rearrangements Resulting in Ring Contraction BY HERBERT 0. HOUSEA N D RICHARD L. WASSON: RECEIVED OCTOBER1, 1956
-4xnetliod is described for the conversion of cyclohexenone derivatives t o the cvrresporidiiig cycl[il)eiit,inoiie derivatives. The procedure involves the isomerization of 2,3-epox~cyclohexanonederivatives to the corresponding a-formyl- or a-acylcyclopentanones accompanied in certain instances by 1,2-cyclohexaiiediones. Isophorone oxide WAS converted t o a mixture of 2,4,4-trimethylcyclopentanone, 2-formyl-2,4,4-trimetliylcyclo;,cntatioxie and 3,5,~-trimet~i~l-l,2-c~-cloliexaxiedioxie. 2,3-Epoxycyclohexanone yielded a mixture of cyclopentanone atid 1,3-cJclohesanedione. 2,3-Epoxy-3-phenylcycloliexanone and 2,3-epoxy-2-rnethylcyclohexanone gave 2-plienylcyclopentan~i1earid Z-acet!.lc!-cl;)pentanorle, respectively. The isomerization of 3-methyl- and 3-phenyI-2,3-epoxycyclopentanorieyielded the corresponding 3-substituted-l,~-c,-clopenta!iediones.
Consideration of the normal course of the acidcatalyzed rearrangement of a,P-epoxy ketones (;.e., acyl migration) suggested that this reaction might provide a useful method for reducing the ring size of cyclic ketones. For example, rearrangement of an epoxy ketone of type I, which is readily accessible zliu the corresponding unsaturated ketone 11, would be expected to yield the keto aldehyde 111. Subsequent cleavage of the formyl group would yield the ketone IV, the over-all result being the loss of a carbon atom adjacent to the carbonyl group.
\A
aldehyde I'Ib not being isolated. None of the a-diketone VIIIb could be isolated from the rcaction mixture. The rearrangement of 2,3-epoxycyclohexanone (Vc) followed by alkaline cleavage produced cyclopentanone VIIc (257,) ; however, the major product was the a-diketone VIIIc (5670). The yields of the two products VIIc and VIIIc were not altered significantly when the oxide Vc was isomerized in the presence of boron trifluoride rather than boron trifluoride etherate.
v' 0
I1
I
\O
I11
\.'o
IY
The series of compounds V was selected to test the applicability of the method for conversion of cyclohexanone derivatives to the corresponding derivatives of cyclopentanone. The isomerization of a benzene solution of isophorone oxide (Va) in the presence of boron trifluoride etherate produced the keto aldehyde VIa (33%) accompanied by the ketone VIIa ( 2 S % ) . The ketone VIIa was presumably formed by the deformylation of VIa during the isolation. A small amount (3Yc)of the enol forin of the a-diketone VIIIa also was formed. Treatment of the keto aldehyde VIa with boiling, ethanolic sodium hydroxide produced the ketone VIIa in 90% yield. A more satisfactory procedure for the preparation of the ketone VIIa involved treatment of the crude reaction mixture from the isomerization with ethanolic sodium hydroxide. This procedure increascd the yield of the desired ketone VIIa (TO-75%) and facilitated separation of the alkali-soluble a-diketone VIIIa. By use of this procedure 2,3-epoxy-3-phenylcyclohexanone (Vb) was converted to %phenylcyclopcntanone VIIb ( G S Y ; ) , thc intermediate keto (1) Alfred P. Sloan Foundation Research Assistant, 1'256,
(2) For previous papers in this series see THISJOURNAL, 76, 1236 (1054); 77, 6525 ( 1 9 3 ) ; 78, 2298, 4394 (1956).
0 VIIIL, It, = Iixersity, 1 ( 6 ) S ~ e u(;'ir
