HH la lb

oo40-4039/89 $3.00 + .OO 3521-3524,1989 Maxwell Pergamon Macmillan plc

Tetrahedron Letters,Vol.30,No.27,pp Printed in Great Britain

SYNTHESIS

AND

STRUCTURE

OF

NOVEL

ALKYLIDENEMALONALDEHYDES:

2-(DIFORMYLMETHYLENE)-1,3_DITHIANE AS

WELL

CHRISTIAN MICHAEL Fachbereich

AS

AND

-1,3-DITHIOLANE

(2,3-DIPHENYLCYCLOPROPEN-1-YLIDENE)MALONALDEHYDE

REICHARDT,:: SCHULZ,

2

Chemie

BERND-VOLKER WERNER der

Hans-Meerwein-StraOe,

2

HERGET, and

MASSA,

’

STEFAN

PESCHEL

Philipps-Universitzt D-3550

Marburg,

Fed.

Rep.

Germany

Summary : The alkylidenemalonaldehydes 4,4-diformyl-1,2-diphenyltriafulvene (41, 2-(diformylmethylene)-1,3-dithiane and -1,3-dithiolane-(8) have been synthesized by various methods, isolated as crystalline substances and studied X-ray analysis.

(11, by

Monosubstituted malonaldehydes are valuable C s-synthons which are completely enol lzed; their reactivity corresponds to that of vinylogous carboxylic acids. Non-enolized alkylidene-malonaldehydes and 2,2_disubstituted malonaldehydes, however, are genuine aliphatic dialdehydes with an enhanced chemical reactiviAs cross-conjugated n-systems, alkyl idenemalonaldehydes J_ are particularly ty. interesting because of their potential ambifunctional reactivity towards electrophiles and nucleophiles.

H

3

H Elektrophile

lb

la

The first alkylidenemalonaldehydes (1: R1 q H; R2 q COzR) have been prepared in situ by Woodward et al. 4 and Used as intermediates in his cephalosporine C synthesis. 5 Alkylidenemalonaldehyde-bisCdimethylacethylacetals) have been synthesized by Reichardt et al., 6 followed by the first syntheses of isolable alkylidenemalonaldehydes by Reichardt et al. 7~8 (benzylidene7 and cycloheptatrienylidene-malonaldehyde 8 and by Arnold et al. 9,lO (aryland diarylalkylidenemalonaldehydes); see reference 1 for a survey of older 1 iterature, and references ll,l* for recent reviews on the chemistry of alkylidenemalonaldehydes.

In syntheses enough cation results.

continuation of our work on aliphatic dialdehydes, of further substituted alkylidenemalonaldehydes to be isolated as crystals and studied by X-ray of Gompper et al. ‘3 gives rise to this preliminary

The idea that structure lb into lidenemalo6ldehyde,

delocalization an aromatic led

to

of ring the

the 14

positive should

synthesis

of 3521

charge stabilize stable

1 we now report which are stable analysis. A recent communication in

the

dipolar

the corresponding C2,4,6-cycloheptatrien-

on

the

publiof our

mesomeric alky-

3522

I-ylidene)malonaldehyde, membered aromatic lonaldehyde. 3 with the subsequent method g brownish-yellow

ring

8 An should

analogous also give

charge delocalization a resonancestabilized

Indeed, acid-catalyzed condensation trimethinium salt 2 in Ac,O/HClOb (70 hydrolysis with lN_HCl at tj5 “C gives (2,3-diphenylcyclopropen-I-ylidene)malonaldehyde crystals with m.p. 183 184 OC

into a threealkylidenema-

of 2,3-diphenylcyclopropenone %> at room temperature - according to Arnold’s 4 with 52% (from cyclohexane).

and yield

as

(I It HCLO, in AczO, - H,O ~21~2H~O~,-2~MeNH,1”C10~ .

,,,C 52 %

0 3

2

4b

4a

The structure of 4 was proven spectrum, and X-ray analysis I> is with I37 pm slightly (Fig. double bond (ca. 134 pm), indicating

mass

Fig.

1.

Crystal 1825

structure reflections).

of

4 ‘5-

by elemental analysis, IR, ‘H, (cf. Fig. 1). The C-l/C-4 bond longer as expected for a normal a small contribution of the

(space

group

PC;

2

=

2;

wR

=

0.056

and

13C

NMR,

length of C(sp2)=C(sp2> dipolar

for

4

3523

form tive

4b. G

The the

plane

of

the

cyclopropene

malonaldehyde

(Z-Diformylmethylene)-1,3-dithiane lithiated Z-trimethylsilyl-1,3-dithiane methylacetal) (5) 16 in extraction with-dichloromethane

(1) tetrahydrofuran-at as follows:

n

OCH,

s f

* H&O

OCH,

Li

slightly

twisted

by

3.5”

x

Illin

s

been obtained by addition to mesoxalaldehyde-1,3-bis(di-70 “C, subsequent hydrolysis

rela-

After

removal of the washed with diethyl m.p. 90 92 OC,

and

12)+ H30@, Room temp. 65 - 75 %

Si(CH,J,

solvent, ether,

of

n

THF, - 78’C

H

6

5

times with

has (6)

0 H&O

is

ring

moiety.

H 7

the to

partially give -7

as

crystalline fine, yellowish

Corresponding 6,6-diformyl-1,3-dithiafulvenes have reaction et al., ‘3 however, starting with “umpol ed” sodium salt of malonaldehyde and 2-methylthio-1,3-dithiolium

product was crystals

been obtained partners such salts.

several (73%)

by Gompper as the

There is even a simpler way to get these alkylidenemalonaldehydes, analogous to Pak et al .: ‘7 direct nucleophillc attack of carbon disulfide by the malonaldehyde anion, followed by a two-fold alkylation reaction of the intermediate anion with l,n-dib;gmoalkanes leads to = 3) and -8 (n = 21, -7 (n however, in rather low yields.

0 K@

DMF.+K,CO,

illin +

S=C=S

12l+Br-ICH4,-~~ II-

IL%

n=2:

8

n=3:

7

The C-2/C-7 bond length of 7 (Fig. 2) is with 139 pm again larger as expected for a normal ~Z(sp~>=C(s~~) double bond (ca. 134 pm), indicating a significant contribution of the dipolar form lb. The SCHAKAL drawing of 7 2) indicates steric interactions betweenthe sulfur and oxygen atoms, (Fig. thus leading to a slightly twisted conformation of 7. The angle between the best planes IC-2/C-7/C-8/O-S/C-9/0-93 and (S-l/C-2/T-3/C-71 is 3.8(Z)“. and C-6 may falsify the geometry of this Disorder of the ring atoms C-4, C-5, region. Acknowledgement: For first successful attempts to synthesize the alkylidenemalonaldehyde 7 in Marburg 1975/76 we thank Dr. E.-U. Wtirthwein, now Professor at tEe Institute of Organic Chemistry, University of Miinster. For the help with the crystal structure determinations we thank Mrs. S. Wocadlo, Marburg. - This work has been supported by the Fonds der Chemischen Industrie, Frankfurt (Main).