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Journal of Organometallic Chemistry, 247 (1983) CS-C7 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands

Prelim~ communication

REGIOCHEMISTRY OF SOME ELE~ROP~LIC CLEAVAGES OF PENTA-2,4-DIENYLSILANES, GERMANES AND STANNANES

MARTIN JONES and WILLIAN KITCHINO*

Department of Chemistty, University of Queensland, Brisbane 4067 (Australia)

(Received February 1st. 1983)

t2,4-Pen~dienyl)- and (2,4-hexadienyl)-t~methyl-sil~es, -germanes and -stannanes experience trifluoroacetolysis regioselectively at the e-position, whereas sulfur dioxide reacts regiospecifically at the r-position of the stan- nanes. The kinetic 7-sulfinate efficiently rearranges to the (conjugated) dienylmethylsulfinates.

Recently we reported that trifluoroacetolysis of 6-alkylcyclohex-2-enyl- silanes, -germanes and -stannanes was regiospecific (r-attack) and stereo- selectively anti [ 11. In contrast sulfur dioxide insertion into these stannanes, although regiospecifically 7, was stereospecifically syn [ 21 e.g. eq. 1. This difference was attributed in part, to a stabilising 09 l l Sn interaction in the transition state for this insertion.

As a prelude to examining the stereochemistry of electrophilic cleavage of 2,4-pentadienylmetallics, it was necessary to establish the regiochemistry of substitution (i.e. 01,~ ore, C e =C--Cr =C--co’ -M) by simple electrophiles. We have examined the reactions of selected systems with CF3COOD and SO2 and the results are herein.

Pentadienyllithium [3] (in THF) was trimethylsilylated (-70°C) to provide a mixture of the trans- and cis-trimethylsilyl-2,Cpentadienes 141, on the basis

0022-328X/83/$03.00 g, 1983 Elsevier Sequoia S.A.

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of GC-MS behaviour and 13C and ‘H NMR spectra. Germylation and stannyi- ation provided very similar mixtures. Silylation and s~nylation of lithium hexadienide proceeds only at the primary carbon, again to give an isomeric mixture. The product distributions are shown in Table 1.

TABLE1

Lithium~entadtsnide Lithiumhexadienide

(CH,),SiCl 88.1 11.9 68.9 28.1 24

(CH,),GeBr 88.2 11.8

fCH,),SnCl 83.4 16.6 66.6 16.1 18.4

Trifluoroacetolysis. The 2H NMR spectrum of the total product consisted of one signal at 6 1.74 ppm, while the r3C spectrum exhibited signals appro- priate for Puns-l,&pentadiene. The product is thus 5-deutero-1,3-pentadiene with no evidence for formation of 1,4-pentadiene, which would result from

CF,COOD

- AA/” (2)

y-attack (eq. 2). Distinction between (Y and E attack was achieved by exam- ining the 2,4-hexadienyl systems, and the results based on 13C and 2H spectra are summarised below. Of additional interest to this predominant e-attack by CF3COOD, was the strong likelihood of significant T-attack on the stan- nane (- 13%) [ 51.

/ CF,COOD

(6 2.09) - 92% (6 1.71 ) -‘8 % (6 2.7) 0 .I.

CF,COOD -80 %

Sulfur dioxide insertions. Reaction of Penn-2,4dienylt~me~yls~n~e with gaseous SO2 provided a sulfinate, characterised by a doublet (2H) at 6 3.1 ppm consistent with eq. 3.

S”/ so /

P-WA/i z AdvSo2sn~ (3).

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The 13C NMR confirmed this overall structure, with the dual ?c-SO, - signals (64.74 and 60.18 ppm) indicating a cia,trans mixture. This result, while not distinguishing between (Y or E attack of SOz, suggested that r-attack was unimportant, in spite of our suggestion that 7-attack might be favoured by possible O*** Sn coordinative stabilisation of the leaving group (formally (CH,),Sn’), this interaction being less likely for the more remote E-attack.

However, careful examination of the hexa-2,4-dienyltrimethylstannane-SO, system (CDC13) confirmed (kinetic) r-attack, with the doubly allylic secondary 7-sulfinate rearranging efficiently to a mixture of the (conjugated) dienyl- methylsulfinates, readily characterised by 13C and ‘H NMR spectra [ 6 1.

/ w SOgAl -

I--- \

/ Sn-

.lppx+/ \ so2- / \

4

/

so2s”\

(8,major)

(A) “y so,sn -

\ (C,minor)

Early NMR observations (after 3 minutes at 0°C) showed A to be char- acterised by a 13C signal for the doubly allylic f C-SOz - at 76.44 ppm and by ‘H signals at 6 3.28 (lH, “t”,>CESO,-) and 5.15 (1H) and 5.27 ppm (1H) for =CH2 . This kinetic product rearranged completely within 30 minutes at 25°C to B (doublet (2H) at 6 3.03 and 13C(~~-SOz -) at 64.95 and 65.71 ppm) and C (S 2.29) (lH, “quintet”, CH3 -C_H--CH=;

S 02- 6 1.17 ppm (C_H,,d).

The mechanism of the A + B + C change remains to be established. The stereochemistry of these e-selective trifluoroacetolyses and r-specific

SO? -insertions is currently under study.

Acknowledgement. Partial funding of this work by the Australian Research Grants Scheme is gratefully acknowledged.

References

G. Wickham and W. Kit&in&J. Org. Chem., in press; G. Wickham and W. Kitchhg. Or6anometallics. in press; See also T. Hayaabi. H. Ito and M. Kumda. Tetrahedron Lett.. 29 (1982) 40s. D. Young and W. Kitcblng. J. Org. Chem.. in pros& (a) R.B. Bates. D.W. Goaeltnk and J.A. Kaczynskt. Tetrahedron Lett.. (1976) 199; (?a) W. Oppolzer, S. Burford. F. Muazu. Helv. Chim. Acta. 63 (1980) 665; (c) W.T. Ford md M. Newcomb. J. Am. Chem. Sot., 96 (1974) 309. D. Seyferth and J. Porn&. J. Org. Chsm.. 46 (1980) 1722. Sakurat hu reported tit aldehyder. ketones and cc&ala reacted selectively at the epositlon of penta- dien~ldlaner. whereas acid chlorides exhibited slgnfftcant r&tack. (A. Hosomi. M. S&o. Ii. Sakurai. Tetrahedron L&t., (1980) 3783. hi. Jones. Honoura The& University of Queensland. 1982.