Tetrahedron betters No. 43, pp 4391 - 4393, 1972. Pergamon Prsss. Printed in Great Rritaia.

NO-XY~ Acid Catalysad Wigs&ions in &Raphthalenones

BernardMiller and Mohsmed R. Saidi

Department of Chemistry, University of Massachusetts, Amherst, Mass., 01002

(Received in USA 16 August 1972) received in UK for publication 22 September 1972)

The normal dienoue-phenol rearrangements of linearly-conjugated cyclohexadienones

(e.g., &+2) are prevented in the a-naphthalenone I.* Instead, a methyl group in 1 mi-

grates to the carbonyl carbon to give carbonium ion 4, which then gives rise to the naph-

thy1 acetate 2. No further migration of a methyl group to give 6 occurs, since formation

of 5 would require disruption of the aromaticity of the second ring.

Cif, CIr,

03 3 / 0

We have now investigated the migrations of ally1 groups in &mphthalenoues. In

these molecules the norm1 major rearrangement pathways - [3,3] migration of the ally1 group

to the position "psra ' to the oxygen atom, or [1,5] migration to the second ortho position

if the pcua position is occupied 3 - would both disrupt the arcmaticity of the secoud ring.

It seemed likely, therefore, that other, povel, reactions might occur in these compounds.

We hnve found that the acid-catalyzed migration of an ally1 group in a &'-naphthalrw-

one does indeed occur by a novel [3,k] shift - a type of migration which has not pretious-

ly been observed in the dienone-phenol rearrangement. In addition, a crotyl group undergoes

both a [j,4] and an effective [1,5] sigvatropic shift, in spite of the apparent necessity

for disruption of the aromatic ring during the rearrangement.

Naphthalenones 1 and E were prepared by Claisen alkylation of l-methyl-2-naphthol. In

comparison with migrations of ally1 groups in monocyclic cyclohexadienones,3 rearrangement

of 1 proceeded extremely slowly, requiring E. 48 hours in a solution of lO$ sulfuric acid

(by volume) in acetic acid at room temperature for essentially complete disappearance of the

starting material. The only products of the reaction were naphthol 9 and its acetate.

4391

4392 No. 43

When the reaction was interrupted after one half-life, the yield of the acetate was only 3%

of that of 2, but the ratio of acetate to naphthol increa6ed with increacliug reaction time.

The structure of 2 wa6 indicated by its nur spcctrm, which showed a singlet for the

proton at C-3 at 66.8 and two distinct sets of aromtic multiplets arouud 5 7.25 and

6: 7.8 gpm - a pattern characteristic of l,h-disubstituted naphthalenes.4 Its structure was

confirmed by reduction to l-arethyl&-propyl-2-naphthol, which wa6 independently synthesized

by reaction of n-propyl mgne6iuu brmide with the acetoxy ketone g.=

Formation of 2 (assuuing it tc be a single rtep reaction) could proceed by either

a [1,4] migration (without inversion of the ally1 group) or a [3,4] aigration (with inversion

of the ally1 group). To distiuguish between the6e two possibilities, the rearrang event of

the crotyl-substituted naphthalenone g was studied. Rearmnge6mnt of g proceeded readily in

1% sulfuric acid-acetic acid at ram tcmparature to give (after 24 hours) three naphthols

identified a6 the cleavage product, 1466thyl-2~naphthol, and the rearraugemmt product6 11

and 12 in yields (vpc) of 45, 24, and 3l$, respectively. haphthol 11 wa6 identified by its

uur spectrum and by reduction to 4-so-butyl-l-methyl-;l-nsphthol, which ~16 sycthesized by

the rmethod used for the IJ-propyl analog. The structure of naphthol 12 was Suggested by its

cur spectruu, which showed the ab6enCe of a proton at C-3, and was confirmed by independent

synthesie from jl-brouo-l-methyl-2-naphthol,e a6 io shown below.

No. 43 4393

The two typea of rearrwnt6 thns appsu caplately regiorpse~flc, rigration to C-4

proceeding with imrersion of the ally1 group snd tigration to C-3 without lnvuaion. As

indicated above, the rlmplest dercriptlon of these processes is as [3,4] and [l,S] si(ptro-

pit shifts, respectively. Both migrations could proceed by multistep processes however - the

[T,‘r] migration by a [1,2] migration followed by a [3,3] migration, and tbe [3,5] migration

by two [1,2] rigrations. No distinction between these paths is yet possible. Two other mul-

tistep mechanisms appsu to be ruled out. 1.Ikthvl-2-naphthol nndergoss electrophilic sub-

stitution preduinantly at ~-6.0, Thns, neither reursngement product could arise via a

cleavue-realkylatia process. We have fomd that ally1 l-methyl-2-naphthyl ethers in acid

give rise to the sams products obtained fru rearrangement of the naphthalenones, but these

rearrangements are appreciably slower than those reported above, and appear to proceed via

the naphthalenones as intersmdiates, rather than the reverse.

Previous observations of acid-catalysed rearrangements of cyclohexadienones indicated

that effective nigrating group8 tend to give reactiona which resemble thermal migrations,

while poorer migrating gronps undergo reactions resembling those which occur in carboni= ion

rearrangements.' The observation that a crotyl group (the better migrator, since it can bear

a positive charge Bore easily) undergoes both a [1,5] shift s and a [3,4] shift in n&s@%-

thalenone, while an ally1 group undergoes omly a [3,4] shift ', Is consistent with our

earlier generalization. One of us has suggested that "thersU" types of migrations proceed

from the nod r&protonat.ed cyclohexsdienones, while-the "cubonium-Ion" migrations pro-

ceed from the higher energy fl-protonated species. While our present results are consistent

with this hypothesis , other interpretations are not excluded.

Acknouledgunts: We thsnh the donors of the Petroleum Research Fund, sdministered by

the American Chemical Society, for a grant in support of this work.

1) 2) 3) 4)

5)

6)

7)

8)

9)

Reactions of C~lohexadlemnes, XXX, M q: B. Miller, Tetrahedron Letters, 1010 (1972) _-_-_--____ E.B. Harvell and J.L Stephenson, J. Amsr. Chem. Sot., u_, 5177 (1955). -~- B. Wller, ibid., 9232 6246 (1970).

e.g., Ssdtler Standard Spectrum Bo. 13910.

F. Wesserly snd F. Sinwel, Monats., -L 81 1455 (1950).

K. Fries and K. Schiubzlschmidt, &., 484, 245 (1930).

B. Miller, J. Amer. Chem. Sot., 92, 6252 (1970). --

Ally1 group8 do not undergo [1,5] shifts in cyclohexadiemes, l nce [3,3] shifts ue much Iy)re rapid [B. Miller, J. Org. C-., 32, 4262 (1970) I. However, c~ioprapylrcthyi groups (B. Miller and K.-H. ti~dmiron Letters 519 (lm2)] and benzyl grups (nn- e-9 publishedwork fra this laboratory) do really undergo sucbreoctions. The tbenrl re- urragernts of0 -napbthalenones are presently under lnrcstigatlon.

Ally1 groups undergo [3,4] ligrations In siwple cyclohexadienyl cuboniu ions [R.-J. Han- sen, B. Sutter and II. SC-d, Helv. Chir. Acta, 2, 828 (1968)].