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Tetrahedron L etters, Vol. 37, No. 6, pp. 853 -856, 1996Copyright 1996 Publishedby ElsevierScience adPrinted n G reat Britain.All righ ts reserved0040-4039/96 $15.00 + 0.00

C / s - d io x o m o l y b d e n u m ( V I ) C o m p l e x es a s N e w C a t a ly s ts f or th eM e y e r -S c h u s t e r R e a r r an g e m e n t .

C h r i s t ia n Y . L o r b e r a n d J o h n A . O s b o r n *

Labom ~ire de C himie des M6laux de Transitionet de Catalyse, as~ ci6 au C.N.R.S., Universilt~Louis P astet~,lnstitut Le B el, 4 rue Blaise Pascal, 67000 Strasbourg,France.

Abstract: We describe a new catalytic system for the isom erisation of propargylic alcohols into ct,[3-ethylenic carb on yl derivatives (Meyer-Schu ster rearrangem ent) l , based on the combination ofdioxomolybdenum(Vl) atalysts~mdsulfoxides,

T h e M e y e r - S c h u s t e r r e a r r a n g e m e n t o f a - a c e t y l e n i c a l c o h o l s ( s c h e m e 1 ) l e a d s t o a , ~ - t m s a t u r a t e d c a r b o n y lc o m p o u n d s w h i c h a r e i m p o r t a n t o r g a n i c i n t e r m e d i a te s , p a r ti c u l a r ly i n t h e s y n t h e s i s o f n a t u r a l p r o d u c t s o fb i o l o g i c al , p h a r m a c e u t i c a l o r c o s m e t i c i n t e r e s t2 ,3 s uc h a s v i t a m i n - A a n d i t s de r i va t i ve s , te r pe ns ( f o r t he s yn t he s i so f v i t a m i n s A , E , K , f l a v o u r s a n d p e r f u m e s ) a n d c a r o t e n o i d s.

S c h e m e 11 ~ R 2 RM e y e r - S c h u s t e rR R , ,H O R e a r r a ng e m e n t I:11 O

T h i s r e a r r a n g e m e n t c a n b e e n a c h i e v e d b y u s i n g a v a r i e ty o f c a t a ly s t s s u c h a s s t ro n g a c i d s w h i c h a r eu n s e l e c t i v e , 1,4 o x o v a n a d i u m ( V ) c o m p l e x e s w h i c h n e e d e l e v a te d t e m p e r a t u re s , 5-7 M o O 3 w h i c h n e e d s a l s oe l e v a t e d t em p e r a t u r e s ( 1 5 0 - 1 7 0 C ) a n d g i v e s o n l y p o o r y i e ld s ,5 n - B u 4 N R e O 4 / p - T s O H w h i c h w o r k s a t 2 5 C b u ti s u n s e l e c t i v e ( d e h y d r a t i o n d u e t o t h e p r e s e n c e o f t h e a c i d ) , s a n d z i c o n i u m ( I V ) c a t a l y s t s i n a s s o c i a t i o n w i thC uC 1. 9 T o da t e , t he b e s t r e s u l t s w e r e ob t a i ne d u s i ng a c a t a l y t i c s y s t e m ba s e d o n t he c o up l e T i ( O R ) 4 / C uC I . 10 , tI n t h e p r e s e n t p a p e r , w e d e s c r i b e t h e u s e o f m o l e c u l a r c i s - d i o x o m o l y b d e n u m ( V I ) c a t a l y s t s t o i s o m e r i s ep r opa r gy l i c a lc oho l s .

I n c o n t r a s t w i t h o x o v a n a d i u m c a ta l y s ts , d i o x o m o l y b d e n u m ( V I ) c o m p l e x e s ( 5 % m o l ) a l o n e d o n o t e a ta l y s et he M e y e r - S c h u s t e r r e a r r an g e m e n t o f 2 - m e t h y l 3 - b u t y n 2 - o l ( m e t h y l b u t y n o l) , o n l y i n c o m p l e t e c o n v e r s i o n b e i n go b s e r v e d i n t h i s c a s e ( s e e fi g u r e 1 ). H o w e v e r , w h e n d i m e t h y l s u l f o x i d e i s u s e d a s s o l v e n t o r c o s o l v e n t ( c a 2e qu i v D M S O / s ub s t r a t e ) , c a ta l y t i c is om e r i s a t i on t a ke s p l a c e a s s how n i n f i gu r e 1 .

O t h e r s u l f o x i d e s , o r p y r i d i n e - N - o x i d e , c a n a s w e l l s e r v e a s p r o m o t e r s ( s e e t a b le 1 ). Y e t o u r b e s t r e s u lt s8 53

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were obtained w ith dibuty lsulfoxid e (entries 1-3).9.12 Bo th ratesand se leedvi ties a re fur the r inc reased by ~a l t io nof a ca ta ly t ic amou nt of ca rhoxyl ic ac id (compare entr ies 1 and 2) . Such an e ffec t has a l ready been ~ e d in theisomerisation o f prop argy lic a lcoho ls catalysed by si loxovanadium 6a or t itanium 7b catalysts.

F i gu re 1 : I some r i s a fi on o f me t hy l bu tyno l .C" CH3 Mo O2(acac)2 (1 equiv.) CH 3 H/ ~ HHO 100C CH3 O

me thylbutynol (20 equiv.) prenal6 0 '5 0 '4 0 '

"~ 30 '2 0 '1 0

0 0- , - , - - . -

5 1 0 1 5 2 0 2 5Time (h )Condi t ions : methy lbutyno l 20 equiv ., MoO2(acac)2 1 equiv . , 100C.(o) solvent : o-C6H4C12; 1 :i ) so lvent : DM SO ; (* ) solv ent : o-C6H4C12 + 40 equiv . D M SO .

A g re a t r a nge o f mo l ybde num pre c u rso r s c a n be use d , e . g . Mo O 2X 2 (X = 1 /2 a c a c , O R, O A r o r C1) ,MoO2(NCS)4(PPh4)2 or even M oO 3. Mo O2(acac)2 appears to giv e the high est isomerisation rate an d selectivity.

The high se lec tiv ity obta ined for m ethylbutynol i s a l so found for o ther te rt ia ry p ropargyl ic a lcohols such as3-methy l 1-pentyn 3-o l (ent r ies 1-6). Where as for more h indered a lcoh ols like t r iphen ylpropa rgyla lcoho l there a c ti on i s ve ry s l ow (e n t ry 7 ). Th i s w a s a l so fou nd fo r va na d i um a nd t i ta n i um c a t al ys ts . The m ol ybde numcatalyst , h ow ever, is unsat isfacto ry for the rearrangem ent of primar y and secon dary alcohols, sinc e side-productsresul t ing f ro m the ox ida t ion of the a lcohol func t ion a re forme d extens ive ly (ent ries 9-10) . The use of the samecouple M oO2X2 / sulfoxide in the catalyt ic oxidat ion o f a lcohols will be prese nted elsewhere. 13

The ge ne ra l me c ha n i sm p ropose d 5 for oxo-m eta l complex ca ta lysed i somerisa t ion o f propargy l ic a lcoholsw o u l d a p p e a r t o a p p l y i n p a r t t o t h e m o l y b d e n u m ( V I ) c a t a l y s i s r e p o r t e d h e r e ( s c h e m e 2 ) :i .e. (1) form at ion of an a lkyn ylox o com plex 1 by t ranses te r if ica tion of the c i s - d i o x o m o l y b d e n u m ( V I ) precursor,fo l l ow e d by (2 ) fo rma t i on o f t he a l l e ny l oxo c ompl e x ~ by a [3 ,3 ] - s i gma t rop i c r e a rra nge me n t (w he re t he oxol igands p lay a key ro le ) v ia a me tal lacyc lic intemzediate , and t he n ( S ) a l kox i de e xc ha nge oc c u rs w i t h a fu r t he rmo lecule of subs tra te , l ibe ra ting the a l lenol which rea rrange to the produ c t v ia a protot ropic shif t. C omp lexes oftype I cou ld be isolated and characterised, but com pou nd s ~ have no t been detected.

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T a b l e 1: C a t a l y t i c s o m e f i s a t i o nof Various Propargylic Alcohols.Conditious

Entry Subswat# Promoter Acid Temp. (*c) Time (h) Produed Yiddt Sdectivity$1 Bu2S=O 100 52 Bu2S--O Ar'CO2HIbi I00 5

i "CH3 ~ H Bu2S=O 140 0.5OH4 DMSOla] 140 15 Py-O Ar'CO2HIb] 100 5

GIla HC H 3 " ~ O

56 9290 9995 9860 7546 99

T2 C'zHs H6 CH ~ ' ~ H Bu2S=O Ar'CO2H[b] 100 5 ~ 73[1 99CHa 0OHPh Ph Ph7 Ph I " - - Ph Bu 2S =O Ar'CO2H[b] 100 5 / L , ~ J~ 10 50Pb oOH

H OHH ~ 18[1 /8 H I ---- CH Bu2S=O 100 5 H O

I HOH "~ ~ el l3 9[,1]O H HH ~ 309 CH3 I = H Bu2S=O 100 5 CHa OI Cl-h~/ _._. H lO[d]H

0Conditions: Substrate 20 quiv, MoO2(acac)2 1 equiv (0,077 M), promoter 40 equiv, o-dichlorobvnzene 2g (solvent).# Commercial products (Aldrich) except for entry 7, q each product were first chancterised by GC-MS analysis, ? in %,GC determination, $ selectivity = (yield]conversion)xl00, [a] solvent: DMSO, [b] Ar,=tBuC6H4 (5 equiv), [1 mixtu~of Z + E, [d] from oxidation of hydroxyl group.Scheme 2: Catalytic cycle 14 O MoO,2X2 HaGII HaC~

C H 3 H C - O H X ~ "M % 0 _4 ,'-I ~ . . 3 ' #, ,. _ / " - X H /H3C~ " " " ~ ' /% O '~ H 3 C I ~ = ' ~ H y C ~ ~ N O H3

H a C I ~ .H O { 0 0r ]" / M o % . /

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Th e presence o f two ox o l igands on the ca ta lys t may b e a t the or ig in of i t s re la t ive e ff ic iency, the secondox o grou p serving as an act ive spectator l igand b y stabil ising the cyclic intermediate (or t ransi tion state). Th e roleo f t he e a rboxy l i c a c i d a nd o f t he su l fox i de rema i ns obsc u re . The l a tt e r ma y se rve t o ma i n t ai n m ol ybde num i noxidation state VI, since reduc tion to lowe r oxida t ion states, tog ether with catalyst deact ivat ion, appears to occu rin i ts absen ce. 15

W e a re c u r re n t l y i nve s t i ga t i ng i n more de t a i l t he me c ha n i sm o f t he r e a r ra nge me n t me d i a t e d by t he semo lybden um ca ta lys ts .R e f e r e n c e s a n d N o t e s1. M eyer , K . H . ; Schus te r , K . C h e m . B e r . 1922 , 5 5 , 819-823 .2 . P a r shal l , G . W . ; N uge n t , W . A . C h e m . T e c h ( U S ) 1988, 376-38 3 and re fe rences the re in .3. M ercier, C.; Chabard~s, P. P u r e A p p l . C h e m . 1994 , 6 6 , 1509-1518 .4 . a ) S w a m i na t ha n , S . ; N a ra ya na n , K . V . C h e m ~ e v . 1971, 429-438 and re fe rences there in .b ) V a r t a ya n , S . A . ; Ba ba ny a n , S . O . R u s s . C h e m . R e v . 1967 , 670-686 .

c ) He i lman, R. ; Glena t , R . A n n . C h i m . 1963, 8 , 175-183.5. Chabard~s, P.; Ku ntz, E.; Varag nat , J . T e t rahe dron 1977 , 3 3 , 1775-1783.6 . a ) Paul ing, H . ; An drew s, D . A . ; Hindley , N , C. He lv . C him . Ac ta 1976 , 5 9 , 1233-1243 .

b ) O l son , G . L . ; Che ung , H . C . ; Morga n , K . D . ; Bore r , R . ; S a uc y , G . H e l v . C h i m . A c t a 1 9 7 6 ,5 9 , 567-585 .

7 . a ) Erm a n , M. B . ; A u rCh e nk o , I .S .; K e i f i ts , L . A . ; D u l ov a , V . G . ; N o v i kov , J . N . ; V o rP i n , M. E .T e t rahe dron L e t t . 1976 , 3 4 , 2981-2984 .b) Erman, M. B. ; Gulyi , S . E. ; Aul 'Chenko, I . S . M e n d e l e e v C o m m u n . 1994 , 89 -89 .

8 . a ) Narasaka , K . ; Hu sama , H . ; Haya shi , Y . C he m . L e t t . 1991 , 1413-1416 .b) Yamano, Y . ; Tobe , C. ; I to , M . J . C he m . Sac . , Pe rk in T rans . 1 1995 , 1895-1904 .

9 . Lorber , C. Y . T h e s i s Univers i t6 Louis Pas teur de S t rasbourg 1 9 9 5 .10. Chabard~s, P. T e t rahe dron L e t t . 1988 , 2 9 , 6253-6256 .11. Lorb er , C. Y . ; Yo uino u M. T. Y . ; Osborn, J . A . to be publi shed.12. T y p ic a l r e ac t ion c ond i t ions : Un der an ine r t a tmosphere , 39 m g of MoO2(acac)2 (0 .119 re tool ) , 200 mg of

2-m ethyl -3 -butyn -2-ol (2 .377 re tool ) , 772 m g of d ibutylsul foxide (4 .754 m mo l) , 156 nag of 4- te r t-butyl -be nz o i c a c i d (0 .594 mm ol ) , 150 mg o f n -nona n e ( i n te rna l s t anda rd , 1 .190 mmo l ) a nd 2 g o f 1 ,2-dichlo robe nzene (solvent ) we re p laced in a sc rew caps v ia l and hea ted to 100 C under s t ir ring. Afte r 5hours , t he y i e l d a nd s e l ec t iv i t y w e re de t ermi ne d by ga s c h roma t og ra phy (c h roma t ogra ph : H P 5890 I I ;c o l um n: H P -1 , m e t hy l s i l ic on gum , 10 m x 0 .53 mm x 2 .65 p .m; de t e c t o r : F ID ) : y i e l d in p re na l 90%(recovered a lcohol : 9%). A fte r 10 hours , the conv ers ion is com ple te : y ie ld in prena l 98%.

13. Lorb er , C. Y . ; Osbo rn, J . A . to be publ i shed.14. N o t a : X = O R, CI , 1 /2 a c a c . . . S u l fox i de l i gands p roba b l y bound t o m ol ybd e num c e n t e r are no t

represented in this scheme.15. In the absence of promo te r , the isom erisa t ion is only s to ichiomet r ic , and a f rac t ion o f the proparg yl ic

a lcohol i s dehydra ted in to enyne .

( Re c e i v e d in Franc e 8 N ov e m be r 1995; ac c e p ted 4 D e c e m be r 1995)