Towards the diastereoselective functionalization of non-racemic acetal derivatives of η6-arylcarbonyl complexes of tricarbonylchromium

C S I R O P U B L I S H I N G

Australian Journal

of Chemistry

Volume 51, 1998

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Aust. J. Chem., 1998, 51, 1083–1096

.

Towards the Diastereoselective Functionalization of

Non-Racemic Acetal Derivatives of ⁶-Arylcarbonyl

Complexes of Tricarbonylchromium

Jackie D. Kendall ^Aand Paul D. Woodgate ^A,B

A

Department of Chemistry, The University of Auckland,

Private Bag 92019, Auckland, New Zealand.

B

Author to whom correspondence should be addressed.

(S)-Butane-1,2,4-triol (2) has been investigated as a potential chiral auxiliary for the formation of

non-racemic acetals derived from ⁶-arylcarbonyl complexes of tricarbonylchromium. Predominantly

the cis dioxan (5) was formed from benzaldehyde, leading to preparation of the ⁶-Cr(CO)₃complex

(16), and of the derived complexes (23) and (24). Lithiation–electrophile quenching of these complexes

gave a mixture of products arising from ortho and benzylic functionalization. Reaction of acetophenone,

or of the ⁶-Cr(CO)₃complexes (45) or (46), with either the triol (2) or its tris(silyl) ether (15) under

conditions of kinetic or thermodynamic control gave an inseparable mixture of acetals.

Introduction

providing a site for inclusion of a stereogenic centre

(either in the acetal ring, or subtended from it).

(S)-Butane-1,2,4-triol was selected for the preparation

of chiral non-racemic acetals derived from benzalde-

hyde and acetophenone; this chiral auxiliary is easily

hydrolysed, enabling the facile synthesis of either

enantiomerically enriched or pure ortho disubstituted

benzaldehyde and acetophenone tricarbonylchromium

complexes. Moreover, the hydroxy group at C 2 can

provide a locus for chelation interaction during the pro-

posed deprotonation–electrophile quenching sequences,

which may be important for optimum diastereoselec-

tion. Initially, synthesis of (S)-butane-1,2,4-triol (2)

was attempted from commercially available (S)-malic

acid (1) via dimethyl (S)-2-hydroxybutanedioate (3).

The diester (3) was made (88%) by standing a solution

of (1) in dry methanol, with hydrochloric acid as a

catalyst, at room temperature for 5 days.⁶Attempted

reduction of the diester to (S)-butane-1,2,4-triol (2)

using sodium bis(2-methoxyethoxy)aluminium hydride

in dry tetrahydrofuran at room temperature for 4

days was unsuccessful, while treatment with sodium

borohydride⁷gave a mixture of products, which pos-

sibly included a monomethyl ester and a lactone.

In contrast, direct reduction of the diacid (1) with

borane–dimethyl sul de⁸in the presence of trimethyl

borate gave the triol (2) in 87% yield.

As part of a continuing program directed at the syn-

thesis and reactions of ( ⁶-arene)tricarbonylchromium

complexes¹we have been interested in utilizing chiral

auxiliaries which confer diastereotopicity on the pairs

of ortho (or meta) hydrogen atoms of the arene. The

consequence of such inequivalence can be utilized in

reactivity discrimination between such pairs in the com-

plex; the resulting ability to functionalize one ortho site

selectively has been applied to the synthesis of chiral

metal-free organic molecules.²One method for exposing

the latent asymmetry relies on the development of

diastereoisomeric transition states during the approach

of a chiral non-racemic base to the ortho hydrogen

atoms, in an overall deprotonation–electrophile quench-

ing sequence.^3,4An alternative method relies on the

attachment of a non-racemic auxiliary to the arene ring

in order to achieve the desired discrimination. Kagan

has recently disclosed⁵the application of a chiral non-

racemic auxiliary derived from (S)-malic acid (1) to

the diastereoselective functionalization of ferrocenecar-

baldehyde. We report here some results that aimed

at extending this work to acetals derived from (S)-

butane-1,2,4-triol (2) and the ⁶-tricarbonylchromium

complexes of benzaldehyde or acetophenone.

Results and Discussion

The synthesis of (2S,4S)-2-phenyl-1,3-dioxan-4-

methanol (5) was attempted from benzaldehyde and

the triol (2) with p-toluenesulfonic acid as the cat-

alyst, by re uxing in toluene in a Soxhlet extractor

containing 4 A molecular sieves.⁹However, none of

the desired product formed. Since transacetaliza-

Aryl carbonyl compounds themselves are not suf-

ciently electron-rich to form ⁶-tricarbonylchromium

complexes in acceptable yield. However, a cyclic

acetal derivative serves the dual purpose of not only

permitting complexation in high yield but also of

Manuscript received 18 March 1998

᭧ CSIRO 1998

0004-9425/98/121083$ 05.00

1084

J. D. Kendall and P. D. Woodgate

tion is often successful when the direct method fails,

(dimethoxymethyl)benzene (4) (from benzaldehyde and

methanol with tungstosilicic acid catalyst,¹⁰62%) was

re uxed with the triol (2) in hexanes under a Dean–Stark

separator, with p-TsOH as the catalyst.¹¹However, the

dimethoxy acetal (4) hydrolysed to benzaldehyde (due

presumably to the water of hydration in p-TsOH), and

gave none of the desired product. In contrast, pyri-

dinium p-toluenesulfonate, which is not hydrated, was

an e cient catalyst. Although Kagan et al.⁵isolated

only the cis dioxan (5), six acetals (the cis and trans

isomers of ve-, six- and seven-membered rings) are

possible from this reaction and four were in fact formed.

and 5 88 ppm, were assigned to (2R,4S)-2-phenyl-

1,3-dioxolan-4-ethanol (6) and (2S,4S)-2-phenyl-1,3-

dioxolan-4-ethanol (7), respectively, since the signal

due to H 2 is down eld in a trans isomer compared

with the cis isomer.¹⁴The mixture of acetals was also

analysed by g.c.–m.s. As expected,¹⁵the retention

time (Table 1) was shorter for the cis isomer of each

pair and each pair of diastereoisomers had nearly iden-

tical but characteristic mass spectra (Experimental),

which were di erent from those of the other pairs.

The minimum conformational energy for each isomer

was computed by using Macromodel (^MM2, Monte

Carlo; Table 1) in an attempt to predict their relative

thermodynamic stabilities. The two dioxolans (6)

and (7) had the lowest computed energies, but they

were not the major products found experimentally,

although the transacetalization reaction had been car-

ried out under conditions of apparent thermodynamic

control.

1

The signal due the benzylic hydrogen in the H n.m.r.

spectrum is unique for each acetal (Table 1); the major

isomer (5) shows this signal at 5 48 ppm.^7,12,13This

structure was consistent with the other ¹H n.m.r. signals

and coupling constants, as determined from decou-

pling experiments. Two less intense peaks, at 5 75

Functionalization of Complexes of Tricarbonylchromium

1085

Table 1. Data for the isomeric acetals (5)–(10)

gave (19) in only 6% yield, which was increased (32%)

by using dimethyl sulfate and NaOH in Et₂O/H₂O

in the presence of tetrabutylammonium iodide,²¹and

increased again (47%) by the use of sodium hydride–

imidazole and then MeI. The ¹H n.m.r. spectrum of

the product, (2S,4S)-4-(methoxymethyl)-2-phenyl-1,3-

dioxan (19), from the latter reaction showed only one

signal due to a benzylic hydrogen atom, and g.c.–m.s.

analysis con rmed that the ether was of higher purity

than the precursor alcohol, the only contaminant being

a trace (c. 1%) of a dioxolan. The use of potassium

hydride as the base with MeI increased the yield further

(57%). Interestingly, the use of silver(^I) oxide and

MeI in N ,N -dimethylformamide²²a orded only the

methyl carbonate (20) (37%). The molecular formula

of (20) was con rmed by accurate measurement of

the molecular ion in the mass spectrum, and the

1

Compound

H 2 (ppm) R_t(min) Ratio (%) Energy (kJ mol

)

(5)

(8)

(6)

(7)

(9)

(10)

5 48

—

5 75

5 88

—

20 33

21 13

21 91

22 48

—

82

2

9

7

—

27 98

25 85

37 67

38 38

1 50

—

0 87

Acetals can also be made under conditions of kinetic

control, at 78 C, from an aldehyde or a ketone and

a 1,2-bis(trimethylsilyl) ether by using trimethylsi-

lyl tri uoromethanesulfonate as the catalyst.¹⁶In

model reactions, benzaldehyde gave 2-phenyl-1,3-

dioxolan (11) (54%) under these conditions by

reaction with the bis(silyloxy) derivative (12) of

ethane-1,2-diol, and also the six-membered ring ana-

logue 2-phenyl-1,3-dioxan (13) (53%) from 2,2,8,8-

tetramethyl-3,7-dioxa-2,8-disilanonane (14).

There-

infrared spectrum included intense absorptions at 1749

fore, the tris(silyl ether) (S)-2,2,9,9-tetramethyl-5-

[(trimethylsilyl)oxy]-3,8-dioxa-2,9-disiladecane (15) was

made (100%) from the chiral non-racemic triol (2) by

using chlorotrimethylsilane and triethylamine,¹⁷and

was then reacted with benzaldehyde and trimethylsilyl

tri uoromethanesulfonate, initially at 78 C (slow)

and then at 42 C for 4 h. The side-chain trimethylsi-

lyl group hydrolysed during workup to give (80%) a

mixture (¹H n.m.r.) of (5) (98%), (6) (1%) and (7)

(1%). This method was also tried with the dimethyl

acetal (4) instead of benzaldehyde at 42 C, but the

crude yield (21%) was much lower and the minor

components were more signi cant [(5), 80%; (6), 12%;

(7), 8%]. Attempted equilibration by re uxing this

mixture overnight in 1,2-dichloroethane with a cat-

alytic amount of pyridinium p-toluenesulfonate was

unsuccessful, the ratios being unchanged.

1

and 1273 cm

(cf. dimethyl carbonate,

1750,

max

1

1270 cm ¹). The signal due to OCH₃in the H n.m.r.

spectrum moved from 3 41 for (19) to 3 79 ppm for

(20). A possible mechanism for the formation of (20)

is outlined in Scheme 1.

Tricarbonyl[(2S,4S)-2-( ⁶-phenyl)-1,3-dioxan-4-me-

thanol]chromium (16) was then synthesized, both from

[(1,2,3,4,5,6- )-benzaldehyde]tricarbonylchromium(17),

and

from

tricarbonyl[(1,2,3,4,5,6- )-(dimethoxy-

methyl)benzene]chromium (18) prepared by re uxing

the dimethyl acetal (4) with Cr(CO)₆in Bu₂O/tetra-

hydrofuran (9 : 1).¹⁸The aldehyde complex (17) was

stirred with the tris(silyl ether) (15) and trimethylsilyl

tri uoromethanesulfonate as catalyst in dry CH₂C1₂

at 42 C and then at 23 C to give (16) in 51%

yield. Similar reaction of the acetal complex (18) gave

(16) in lower yield (32%), the major product being the

⁶-Cr(CO)₃complex of the major dioxan component

(5) obtained from reaction of the non-complexed arene.

Protection of the hydroxy group in the 1,3-dioxan (5)

was then attempted by using several methods, but with

limited success (di culties in methylating the hydroxy

group of dimethyl (S)-2-hydroxybutanedioate (3) with

a base and MeI have been reported recently;¹⁹only a

low yield of the ether was obtained, together with a

large amount of ole nic esters). Unexpectedly, treat-

ment of (5) with BuLi in dry tetrahydrofuran at 78 C

and quenching with MeI returned starting material.

Powdered KOH and MeI in dry dimethyl sulfoxide²⁰

In order to provide an alternative side chain having

either a directing chelating or steric e ect during

the proposed complexation–deprotonation–electrophile

quenching sequence, the preparation of (2S,4S)-4-

(methoxymethoxymethyl)-2-phenyl-1,3-dioxan (21) from

alcohol (5) was investigated, but again only very

low yields were obtained.

Thus, treatment of

(5) with N -ethyldiisopropylamine and bromomethyl

methyl ether gave (21) (15%), benzaldehyde (30%)

and starting material (23%).

The use of dried

K₂CO₃and a catalytic amount of 18-crown-6²³with

BrCH₂OCH₃produced mainly benzaldehyde, as did

stirring overnight in dimethoxymethane with a catalytic

1086

J. D. Kendall and P. D. Woodgate

amount of p-TsOH. The synthesis of (2S,4S)-4-[(t-

butyldimethylsilyl)oxy]methyl-2-phenyl-1,3-dioxan (22)

was more successful, treatment of the alcohol (5) with

1,8-diazabicyclo[5.4.0]undec-7-ene and Bu^tMe₂SiCl²⁴

giving (22) in 45% yield.

These results indicate that BuLi is a more selective

base than Bu^tLi for deprotonation of (16) because

it removes fewer benzylic hydrogen atoms, it gives a

greater proportion of the product from deprotonation

of just one aromatic site, and there is no evidence

that it behaves as a nucleophile. The BuLi/D₂O

experiments were repeated in diethyl ether as the

solvent at 42 C. The stable yellow complex obtained

after workup contained (¹H n.m.r., mass spectrometry)

0 1 deuterium atoms in the benzylic position and 0 4

in the ortho aromatic sites. Thus, tetrahydrofuran is

preferred to Et₂O as solvent during the deprotonation

reaction as judged from the use of deuterium as the

electrophile.

When Me₃SiCl was used as electrophile after depro-

tonation with BuLi at 78 C both tetrahydrofuran

and diethyl ether as solvent gave a brown oil. Flash

chromatography within 10 min of workup produced the

largest amounts of the intact product complex, which

was relatively stable. If the crude reaction mixture was

allowed to stand under nitrogen for 1 h, a large amount

of decomplexation took place. Chromatography of the

crude product from reaction in tetrahydrofuran gave

three fractions. The two smaller fractions were identi-

ed as a mixture (15%) of the silyl ether complex (25)

and its free ligand (26) and a mixture (10%) of the

2-trimethylsilyl complex (27) and its free ligand (28).

Products (25)/(26) showed no change in the aromatic

region of the ¹H n.m.r. spectrum from the starting

material (16). The presence of a singlet at 0–0 5 ppm

in the ¹H n.m.r. spectrum and the characteristic

The tricarbonylchromium complexes of the alcohol

(5), of the methyl ether (19) and of the silyl ether (22)

were made by the usual thermally promoted method¹⁸

to give (16), tricarbonyl[(2S,4S)-4-(methoxymethyl)-2-

(

⁶-phenyl)-1,3-dioxan]chromium (23), and tricarbonyl-

6

{(2S,4S) -4 -[(t -butyldimethylsilyl)oxy]methyl - 2-(

-

phenyl)-1,3-dioxan}chromium (24), respectively. Puri -

cation of these complexes was di cult because the R_F

value of each was similar to that of the parent ligand,

and ash chromatography required the complexes to

be in solution (Et₂O or CH₂Cl₂) where they were

somewhat unstable (even under N₂pressure and in

the absence of light). Each ⁶-Cr(CO)₃complex was

isolated as a yellow oil. Although (16) solidi ed after 1

month, and could be recrystallized by vapour di usion

using hexanes–CH₂Cl₂, e orts to obtain a single crystal

for X-ray crystallographic analysis were frustrated by

its reversion to an oil on attempted drying of the

crystals by means of an oil pump.

With the tricarbonylchromium complexes of the cis

1,3-dioxan (5) and some of its derivatives in hand, some

lithiation and electrophile quenching reactions were

investigated. Thus, (16) was treated with BuLi or with

Bu^tLi in tetrahydrofuran at 78 C, and the reaction

mixture quenched with D₂O. The reaction mixture

with BuLi remained yellow during the entire process,

but when Bu^tLi was used the mixture turned brown

before workup and the crude product was therefore

decomplexed by exposing the solution to air and sun-

absorbances in the infrared spectrum near 1250 and

1

840 cm

con rmed the presence of a trimethylsilyl

1

group. The aromatic region of the H n.m.r. spectrum

of the arylsilanes (27)/(28) was signi cantly di erent

from that of the starting material, which suggested that

a trimethylsilyl group was attached to the aromatic

ring at an ortho site [note that structures (27), (29),

and (31) do not represent the absolute con guration of

electrophile incorporation]. Two SiMe₃singlets with

similar integrated areas (0 35, 0 38 ppm) may repre-

sent diastereoisomeric ortho products. Alternatively,

they may be due to the complexed and uncomplexed

products (27) and (28). The major fraction (40%)

was also a mixture of complexed and uncomplexed

acetals, a high-resolution mass spectrum con rming

the incorporation of both one SiMe₃group (m/z 402)

and two SiMe₃groups (m/z 474). The ¹H n.m.r.

spectrum (CDCl₃or C₆D₆) was di cult to assign due

to the presence of both complexed and uncomplexed

products, and due to overlap of the signals due to

benzylic hydrogens with those of aromatic hydrogens

in an ⁶-Cr(CO)₃complex. Decoordination of the

tricarbonylchromium group by exposure of a solution

of this fraction to air and sunlight simpli ed the

spectrum (and also partially hydrolysed the O–SiMe₃

group). The original major fraction was then assigned

as containing mainly the complex (29) and its free

light. In each case a large O–H peak was present in the

1

infrared spectrum and no O–D peak (2400–2600 cm

)

was detected; therefore the deuterium was bound to

carbon. The decomplexed product from lithiation

with Bu^tLi contained (¹H n.m.r., mass spectrometry)

0 35 benzylic deuterium atoms and 0 78 aromatic

deuterium atoms per molecule. The mass spectrum

also included a weak signal at m/z 250, corresponding

to the molecular ion from addition of t-butyl carbanion

to the complex. When BuLi was used as the base, there

were (¹H n.m.r., mass spectrometry) 0 13 benzylic

deuterium atoms and 0 82 ortho aromatic deuterium

atoms incorporated per molecule (Table 2). There was

no signal at m/z 250 due to the product resulting

from nucleophilic attack of t-butyl carbanion.

Table 2. Deuterium incorporation (%) in (5) (with

tetrahydrofuran as solvent)

Deuterium position

No D

Benzylic D

Bu^tLi

BuLi

0

22

39

5

26

8

12

6

62

5

13

2

1 Aromatic D

Benzylic and 1 aromatic D

2 Aromatic D

Benzylic and 2 aromatic D

Functionalization of Complexes of Tricarbonylchromium

1087

ligand (30), together with a small amount of the aryl-

silanes (27)/(28) which resulted from partial hydrolysis

during or after the chromatographic separation.

When this reaction was repeated in diethyl ether,

one major fraction was isolated after immediate ash

chromatography. A high-resolution mass spectrum

(c.i., NH₃) of the decomplexed fraction identi ed prod-

ucts incorporating both one and two SiMe₃groups

(MH⁺267 and 339, respectively). G.c.–m.s. showed

two arylsilane products (27) and (28); (30) was also

shown to contain a silyl ether. As an aid to determine

the preferred direction of diastereoselectivity, the two

proposed lithiated intermediates were modelled (Cerius,

Universal Force Field). The relative energy minima

indicate that abstraction of the pro-S hydrogen is

preferred over abstraction of the pro-R hydrogen by

27 6 kJ mol ¹. Kagan et al.⁵demonstrated exclusive

pro-S hydrogen removal from a ferrocene analogue

experimentally, supporting the relative total energies

of the computed lithiated intermediates in the present

case.

One problem associated with the lithiation reac-

tions described above arises from the stabilizing e ect

of the tricarbonylchromium moiety on a benzylic

34

anion.²⁸

Therefore, preparation of the acetophe-

none analogue of (16) was investigated. In contrast

to the result obtained from benzaldehyde, re uxing

(1,1-dimethoxyethyl)benzene (32) with the non-racemic

triol (2) and pyridinium p-toluenesulfonate in hexanes

gave a mixture of six cyclic acetals (33)–(38) in

which no single isomer predominated. The minimum

conformational energy of each acetal was computed

(Macromodel), the results (Table 3) suggesting that

the most stable are the two dioxolans (35) and (36),

followed by the trans dioxan (34) (trans refers to the

relationship between the alcohol-containing side chain

and the phenyl group). This is consistent with the

report³⁵that the diastereoisomer of 2,4,6-trimethyl-

2-phenyl-1,3-dioxan having the three methyl groups

equatorial and the phenyl group axial is more stable

than the epimer with an equatorial phenyl group.

Table 3. Computed minimized energies of

(33)–(38)

Methylation of the complexed aryllithium would

allow the direction and extent of diastereoselectivity

of ortho lithiation to be determined experimentally.

Thus, hydrolysis of the resulting acetal would give the

1

Compound

Energy (kJ mol

)

(33)

(34)

(35)

(36)

(37)

(38)

10 27

27 08

37 28

39 17

3 61

⁶-Cr(CO)₃complex(es) of 2-methylbenzaldehyde, of

27

known absolute con guration.²⁵

Therefore, iodome-

thane was used as the electrophile (BuLi or Bu^tLi,

78 C; or 78 to 0 to 78 C then MeI; or transmet-

allation to an arylcopper then MeI). However, only the

starting complex and its parent ligand were recovered.

Methyl tri ate as the electrophile (BuLi, Et₂O, 78 C)

gave the aldehyde (17) (26%; via attack of the hard

methyl cation on an acetal oxygen) and the O-methyl

ether (23) (48%). Warming to either 23 or 0 C

before the addition of methyl tri ate at 78 C did

give a product of aromatic methylation, decomplexed

(31), but only in very low yield (3 and 4% respectively)

and contaminated by decomplexed (23) (32 and 18%

respectively). These results indicate that, although

excess of BuLi had been used, the alcohol complex

(16) is not a suitable substrate for arene lithiation.

However, treatment of the methyl ether derivative

(23) with BuLi at 42 C and then with D₂O did

not result in deuteration, and use of Me₃SiCl as the

electrophile at 78 C resulted only in recovery of the

starting complex (13%) together with its parent ligand

(26%). Although the complexed t-butyldimethylsilyl

derivative (24) gave better results (BuLi, 42 C; D₂O),

the crude yellow oil incorporating (¹H n.m.r., mass

spectrometry) 0 5 deuterium atoms per molecule and

only at an ortho site, this is still not su cient for use

of this method for further syntheses. Overall, this set

of results shows not only that the optimum conditions

for arene lithiation/electrophile quenching are unique

for each individual tricarbonylchromium complex, but

also that the chemical yields are too low and any

diastereoselection is therefore of little value.

4 02

Comparison of selected peak heights in the ¹³C

n.m.r. spectrum indicated that mainly three isomers

were present. The mixture of acetals was subjected

to g.c.–m.s., the relative peak areas (Table 4) being

consistent with the ¹³C n.m.r. data. From the mass

spectra the pairs of diastereoisomers could be identi ed,

but the ring size of each pair could not be determined

unequivocally.

Table 4. G.c.–m.s. data for (33)–(38) (thermody-

namic mixture)

R_t(min)

Area (%)

Diastereoisomers

8 73

9 18

9 63

10 09

10 78

16 0

3 0

39

41

1

(33) or (34)

(37) or (38)

(35) or (36)

(37) or (38)

The only signi cant di erences between the mass

spectra were a fragment with m/z 131 for the single

diastereoisomer (33) or (34), and fragments with m/z

121 for the pair of diastereoisomers (37)/(38). Since

m/z 131 represents the loss of the phenyl group, this

can occur from a compound with any of the ring sizes.

Similarly, the fragment with m/z 121 (PhCO⁺) is

possible from any of the acetals. In order to simplify

the structural assignment, the methoxy derivatives

(39)–(44) were made (52%) from the mixture (33)–(38)

1088

J. D. Kendall and P. D. Woodgate

by treatment with sodium hydride and MeI. The

resulting methyl ethers were subjected to g.c.–m.s.,

and their mass spectra were su ciently di erent so

that the ring sizes could now be determined (Table 5).

The ¹³C n.m.r. peaks for the three major isomers

(Table 7) were assigned by comparison of the spectra

of the mixtures formed under either kinetic or thermo-

dynamic control. The signal sets for each dioxolan (35)

and (36) are very similar, re ecting the diastereoiso-

meric nature of these acetals. The other major isomer

was con rmed as dioxan (34) by comparison of its

¹³C n.m.r. data with those of the cis dioxan (5) [C 5;

26 41 ppm for (34), 26 7 ppm for (5)].

Frustratingly, separation of the mixture containing

(34)–(36) on a preparative scale by ash chromatography

could not be achieved. In an attempt to enable res-

olution, the ( ⁶-arene)tricarbonylchromium complexes

were prepared [Cr(CO)₆, Bu₂O/tetrahydrofuran, 35%]

from the acetal mixture resulting from thermodynamic

control, but these derivatives were also inseparable

(t.l.c.; hexanes/diethyl ether, 1 : 1, 14 elutions, one

spot). A further attempt involved preparation of

the t-butyldimethylsilyl ethers (Bu^tMe₂SiCl, Prⁱ₂NEt,

20 h, room temp., 36%) of the complexed acetals,

but again these derivatives could not be separated by

column chromatography.

Improvement of the yields from the kinetically con-

trolled acetalizations was then investigated by utilizing

the tricarbonylchromium complexes (45) and (46) as sub-

strates. During the preparation of the acyclic acetal com-

plex (46) from (32) [Cr(CO)₆, Bu₂O/tetrahydrofuran]

small amounts of the acetophenone complex (45) and of

tricarbonyl[(l -methoxyethenyl) - ⁶-benzene]chromium

(47) were also formed. The acetalization of complex

(45) proceeded faster than that of acetophenone itself,

but the yield ( 23 C, 5 5 h, 7%) was still too low.

Similar treatment of the complex (46) gave (48)–(53)

in only moderate yield (34%).

The envisaged application of this chemistry to the

selective functionalization of an ⁶-Cr(CO)₃complex

of acetophenone was frustrated because in none of the

approaches investigated could a single acetal be made,

with either kinetic or thermodynamic control a ord-

ing an inseparable mixture of mainly the same three

isomers. Although the benzaldehyde-derived acetal

complex (16) could be obtained pure, deprotonation

followed by quenching with either Me₃SiCl or MeI was

neither regioselective nor high yielding. Consequently,

(S)-butane-1,2,4-triol is not a useful non-racemic chiral

auxiliary for the diastereoselective functionalization

of ( ⁶-arene)tricarbonylchromium complexes of either

benzaldehyde or acetophenone under the conditions

reported.

Table 5. Products from the methylation of

(33)–(38) (thermodynamic mixture)

R_t(min)

Area (%)

Compound

7 75

7 85

8 05

9 48

9 56

9 79

19

33

38

4

1

(40)

(41) or (42)

(43) or (44)

(39)

Only the two dioxepans (43)/(44) gave mass spectra

which contained a peak at m/z 72 but not at m/z

45 (CH₂=O⁺CH₃). Only the dioxolans (41)/(42) and

dioxans (39)/(40) can produce the latter fragment

without rearrangement; similar initial fragmentation

of (43)/(44) leads to m/z 72. The dioxans (39)/(40)

were distinguished from the dioxolans (41)/(42) by

the peak at m/z 177 (M 45; stabilized more by

resonance when produced from a dioxan rather than

from a dioxolan).

In an attempt to minimize the number of acetals

formed, acetalization of acetophenone was also at-

tempted under kinetic control with trimethylsilyl tri-

uoromethanesulfonate as the catalyst.¹⁶In contrast

to benzaldehyde, the reaction with the tris(silyl ether)

(15) was very slow ( 42 to 10 C, 31 h, 5% conver-

sion). Reaction of (1,1-dimethoxyethyl)benzene (32) to

give the acetal mixture (39)–(44) by the same method

was much faster, ( 42 to 23 C, 8 h, 46%). The

three major isomers present in the thermodynamically

controlled reaction were again formed, although in a

di erent ratio (g.c.–m.s.) (Table 6).

Table 6. G.c.–m.s. data for (33)–(38) (kinetic mixture)

R_t(min)

Area (%)

Compound

9 14

10 02

10 46

34

33

14

(34) (trans-dioxan)

(35) or (36) (dioxolan)

Table 7. ¹³C n.m.r. peaks for the major acetals (34)–(36)

Posi-

tion

trans-Dioxan

(34)

Dioxolan Dioxolan

(35) or (36) (36) or (35)

Cipso

Co and Cm

140 86

128 66

126 64

127 55

70 72

143 22

128 08

125 04

127 71

74 44

144 18

127 99

124 91

127 65

75 35

Experimental

Cp

C 4

For general experimental details see ref. 1.

C 5 and CH₂OH

26 41

69 24

59 97

69 76

60 03

Dimethyl (S)-2-Hydroxybutanedioate (3)

C 6 and CH₂OH

65 78

60 59

(S)-Malic acid (1) (5 03 g, 37 5 mmol) was dissolved in

dried methanol (60 ml), and concentrated hydrochloric acid

(3 drops) added. The solution was left at room temperature

for 5 days before silver(^I) oxide (1 spatula) was added, and

C 4–CH₂

C 2–CH₃

35 91

28 17

35 53

28 05

32 67

Functionalization of Complexes of Tricarbonylchromium

1089

the silver salts were ltered o . Workup and distillation (b.p.

90–100 C/>1 mmHg, lit.³⁶88–91 C/3 mmHg) gave dimethyl

(S)-2-hydroxybutanedioate (3) as a colourless liquid (5 32 g,

followed by benzaldehyde (0 040 ml, 0 394 mmol). After stir-

ring at this temperature for 3 h, the solution was warmed

to 42 C for 4 h. Pyridine (3 drops) was added and the

solution warmed to room temperature, poured into saturated

aqueous NaHCO₃, and extracted three times with Et₂O.

Workup gave predominantly (2S,4S)-2-phenyl-1,3-dioxan-4-

methanol (5) (61 mg, 80%) as part of a mixture [(5)/(6)/(7)

88%).

1109 cm

3464 (OH), 2958, 1738 (C=O), 1440, 1222, 1173,

max

1

.

2 82–2 89 (d, J 4 2 Hz, (H 3)₂); 3 68 (br s,

H

OH); 3 72 (s, OMe); 3 81 (s, OMe); 4 50–4 58 (dd, J 6 1,

4 7 Hz, H 2). 38 3 (C 3); 51 8 (OMe); 52 6 (OMe); 67 1

(C 2); 170 9 (C 1 or C 4); 173 6 (C 1 or C 4).

C

98 3 : 1 1 : 0 6].

5 53 (s, 0 983H, H 2 of (5)); 5 81 (s,

H

0 011H, H 2 of (6)); 5 94 (s, 0 006H, H 2 of (7)).

(S)-Butane-1,2,4-triol (2)

(^C) A solution (1 0 ml) of trimethylsilyl tri uoromethanesul-

fonate (0 05 ml, 0 26 mmol) in dry CH₂Cl₂(10 0 ml) was cooled

to 42 C. The dioxadisiladecane (15) (160 mg, 0 497 mmol) was

added, followed by (dimethoxymethyl)benzene (4) (0 075 ml,

0 50 mmol). The solution was stirred at this temperature

for 4 h before pyridine (4 drops) was added. Workup and

ash chromatography (hexanes/Et₂O, 1 : 1) gave predominantly

(2S,4S)-2-phenyl-1,3-dioxan-4-methanol (5) (20 mg, 21%) as

part of a mixture [(5)/(6)/(7) 80 : 12 : 8].

A solution of (S)-malic acid (1) (1 014 g, 7 57 mmol) in

dry tetrahydrofuran (5 0 ml) was added slowly to a solu-

tion of BH₃.SMe₂(2 2 ml, 23 mmol) and B(OMe)₃(2 5 ml,

22 mmol) in dry tetrahydrofuran (5 0 ml), and then cooled

in an ice–water bath. The mixture was left to stir at room

temperature overnight. Methanol (6 ml) was added slowly and

the solvents were removed; this process was repeated with

more methanol (10 ml) to leave a colourless oil. Distillation

(b.p. 152 C/0 4 mmHg, lit.³⁷120–130 C/0 1 mmHg) a orded

2,2,7,7-Tetramethyl-3,6-dioxa-2,7-disilaoctane (12)

(S)-butane-1,2,4-triol (2) (0 698 g, 87%).

3355 (OH),

(CD₃OD) 1 51–1 80 (m, (H 3)₂);

max

1

2936, 1427, 1059 cm

.

A solution of ethane-1,2-diol (100 mg, 1 62 mmol) in CH₂Cl₂

(8 0 ml) was cooled in ice–water. Me₃SiCl (0 52 ml, 4 1 mmol)

then Et₃N (0 68 ml, 4 9 mmol) were added dropwise. After

the solution was stirred for 2 h at room temperature, Et₂O

was added, the mixture ltered and the solvents were removed.

This procedure was repeated three times to leave the dioxadis-

H

3 42–3 52 (m, (H 4)₂); 3 65–3 83 (m, (H 1)₂, H 2).

(Dimethoxymethyl)benzene (4)

Benzaldehyde (2 9 ml, 29 mmol) and tungstosilicic acid

(100 mg, 0 03 mmol) were dissolved in dry methanol (30 ml)

and stirred at room temperature for 20 min. NaBH₄(0 20 g,

5 3 mmol) was then added slowly. Workup and distilla-

tion (b.p. 40–45 C/<1 mmHg, lit.³⁸56–57 C/3 5 mmHg) gave

ilaoctane (12) (0 208 g, 63%).

1148, 1099, 956, 841 (Si–C), 748 cm

3 82 (s, (H 4)₂, (H 5)₂). 0 5 (SiMe₃); 63 9 (C 4, C 5).

2958, 2868, 1252 (Si–C),

max

1

.

0 30 (s, SiMe₃);

H

C

(dimethoxymethyl)benzene (4) (2 73 g, 62%).

2830, 1454, 1355, 1206, 1105, 1055, 982, 912, 746 cm

3 30 (s, 2 OMe); 5 37 (s, Ph–CH); 7 28–7 39 (m, Hm, Hp);

7 39–7 48 (m, Ho). 52 4 (OMe); 102 9 (Ph–CH); 126 5

2937,

max

2-Phenyl-1,3-dioxolan (11)

1

.

H

A solution (1 0 ml) of trimethylsilyl tri uoromethanesul-

fonate (0 03 ml, 0 16 mmol) in dry CH₂Cl₂(10 0 ml) was cooled

to 78 C. The dioxadisilaoctane (12) (148 mg, 0 718 mmol)

and then benzaldehyde (0 075 ml, 0 74 mmol) were added.

The solution was stirred for 4 h before pyridine (3 drops) was

added. Workup a orded 2-phenyl-1,3-dioxolan (11) (58 mg,

C

(Co or Cm); 128 0 (Co or Cm); 128 2 (Cp); 137 9 (Cipso).

(2 S,4 S)-2-Phenyl-1,3-dioxan-4-methanol (5)

(^A) (Dimethoxymethyl)benzene (4) (0 85 ml, 5 7 mmol),

(S)-butane-1,2,4-triol (2) (0 500 g, 5 6 mmol) and pyridinium

p-toluenesulfonate (1 spatula) were re uxed in hexanes (20 ml)

under a Dean–Stark separator for 7 h. Workup and ash chro-

matography (hexanes/Et₂O, 1 : 1) gave predominantly (2S,4S)-

2-phenyl-1,3-dioxan-4-methanol (5) (0 97 g, 89%). m/z 194

(55%, M⁺); 193 (59, M H); 163 (77, M CH₂OH); 107 (54);

105 (100, PhCO⁺); 91 (56, PhCH₂⁺); 79 (65); 77 (62, Ph⁺); 71

54%).

698 cm

2885, 1702 (PhCHO), 1458, 1400, 1220, 1069,

3 98–4 19 (m, (H 4)₂, (H 5)₂); 5 81 (s, H 2);

max

1

.

H

7 32–7 41 (m, Hm, Hp); 7 44–7 51 (m, Ho); 10 02 (s, 0 06H,

PhCHO). 65 3 (C 4, C 5); 103 7 (C 2); 126 4 (Co or Cm);

128 3 (Co or Cm); 129 2 (Cp); 129 7 (Cipso).

C

2,2,8,8-Tetramethyl-3,7-dioxa-2,8-disilanonane (14)

(65, C₄H₇O⁺).

1141, 1104, 1066, 1026, 758, 700 cm

3418 (OH), 2925, 2862, 1455, 1397, 1365,

1

A solution of propane-1,3-diol (121 mg, 1 59 mmol) in

CH₂Cl₂(8 0 ml) was cooled in ice–water. Me₃SiCl (0 54 ml,

4 2 mmol) then Et₃N (0 70 ml, 5 0 mmol) were added drop-

wise. After 7 h, Et₂O was added, the slurry was ltered and

the solvents were removed (three times) to leave the dioxadis-

max

.

1 32–1 39 (d, J

H

13 2 Hz, H 5eq); 1 76–1 88 (qd, J 12 4, 5 2 Hz, H 5ax); 2 70

(br s, OH); 3 54–3 60 (d, J 5 0 Hz, CH₂OH); 3 85–3 95 (m,

H 4ax, H 6ax); 4 20–4 27 (ddd, J 11 4, 5 2, 0 9 Hz, H 6eq);

5 48 (s, H 2 of (5)); 5 75 (s, 0 045H, H 2 of cis-dioxolan (6));

5 88 (s, 0 035H, H 2 of trans-dioxolan (7)); 7 30–7 38 (m, Hm,

ilanonane (14) (0 328 g, 94%).

1

2957, 2870, 1251 (Si–C),

0 30 (s, SiMe₃); 1 86–2 00

H

max

1092, 840 (Si–C), 747 cm

.

(p, J 6 3 Hz, (H 5)₂); 3 81–3 89 (t, J 6 2 Hz, (H 4)₂, (H 6)₂).

Hp); 7 45–7 49 (dd, J 7 5, 1 8 Hz, Ho).

26 7 (C 5); 65 3

C

0 6 (SiMe₃); 35 5 (C 5); 59 1 (C 4, C 6).

C

(CH₂OH); 66 4 (C 6); 77 4 (C 4); 101 1 (C 2); 126 0 (Co);

128 1 (Cm); 128 8 (Cp); 138 2 (Cipso). G.c.–m.s. (125 C

for 20 min, 6 C per min to 250 C, 250 C for 15 min): 20 33

min [82%; m/z 194 (41%), 193 (50), 163 (70), 105 (100), 91

(42), 79 (64), 77 (67), 71 (43); due to (2S,4S)-2-phenyl-1,3-

dioxan-4-methanol (5)]; 21 13 min [2%; m/z 194 (34%), 193

(52), 163 (57), 105 (100), 91 (48), 79 (66), 77 (75), 71 (52),

44 (88); due to (2R,4S)-2-phenyl-1,3-dioxan-4-methanol (8)];

21 91 min [9%; m/z 194 (41%), 193 (76), 123 (26), 105 (100),

91 (61), 77 (59), 71 (98), 43 (89); due to (2R,4S)-2-phenyl-1,3-

dioxolan-4-ethanol (6)]; 22 48 min [7%; m/z 194 (40%), 193

(59), 123 (34), 105 (100), 91 (58), 77 (58), 71 (97), 43 (9); due

to (2S,4S)-2-phenyl-1,3-dioxolan-4-ethanol (7)].

2-Phenyl-1,3-dioxan (13)

A solution (1 0 ml) of trimethylsilyl tri uoromethanesul-

fonate (0 05 ml, 0 26 mmol) in dry CH₂Cl₂(10 0 ml) was cooled

to 78 C. The dioxadisilanonane (14) (0 215 g, 0 977 mmol)

and then benzaldehyde (0 10 ml, 0 99 mmol) were added.

The solution was stirred at this temperature for 3 5 h then

at 42 C for 3 h. Pyridine (5 drops) was added and the

colourless solution warmed to room temperature. Workup gave

2-phenyl-1,3-dioxan (13) as a colourless liquid (84 mg, 53%).

2958, 2850, 1702 (PhCHO), 1454, 1377, 1146, 1103,

max

1

1006, 744, 696, 640 cm

.

1 36–1 48 (dtt, J 13 5, 2 6,

H

(^B) A solution (1 0 ml) of trimethlsilyl tri uoromethanesul-

fonate (0 05 ml, 0 26 mmol) in dry CH₂Cl₂(10 0 ml) was cooled

to 78 C. (S)-2,2,9,9-Tetramethyl-5-[(trimethylsilyl)oxy]-3,8-

dioxa-2,9-disiladecane (15) (127 mg, 0 394 mmol) was added,

1 5 Hz, H 5eq); 2 18–2 34 (dtt, J 13 4, 12 3, 5 1 Hz, H 5ax);

3 88–4 05 (td, J 12 0, 2 5 Hz, H 4ax, H 6ax); 4 20–4 32 (ddt,

J 10 5, 5 0, 1 3 Hz, H 4eq, H 6eq); 5 49 (s, H 2); 7 30–7 41

(m, Hm, Hp); 10 01 (s, 0 01H, PhCHO).

25 7 (C 5); 67 3

C

1090

J. D. Kendall and P. D. Woodgate

(C 4, C 6); 101 6 (C 2); 125 9 (Co or Cm); 128 2 (Co or Cm);

128 7 (Cp); 138 7 (Cipso).

(^C) A solution (1 0 ml) of trimethylsilyl tri uoromethanesul-

fonate (0 05 ml, 0 26 mmol) in dry CH₂Cl₂(10 ml) was cooled

to 42 C. The dioxadisiladecane (15) (154 mg, 0 478 mmol)

was added followed by a solution of the tricarbonylchromium

complex (18) (136 mg, 0 472 mmol) in dry CH₂Cl₂(1 0 ml).

The mixture was stirred for 7 h before Et₃N (3 drops) was

added. Workup and ash chromatography (hexanes/Et₂O, 1 : 2)

gave the tricarbonylchromium complex (16) (50 mg, 32%).

(S)-2,2,9,9-Tetramethyl-5-[(trimethylsilyl)oxy]-3,8-dioxa-

2,9-disiladecane (15)

A solution of (S)-butane-1,2,4-triol (2) (0 522 g, 4 92 mmol)

in CH₂Cl₂(20 ml) was cooled in an ice bath. Me₃SiCl (2 20 ml,

17 3 mmol) and then Et₃N (3 10 ml, 22 3 mmol) were added

dropwise to the stirred solution. Et₂O was added after 7 h, the

reaction mixture ltered and the solvents were removed. More

Et₂O was added, the slurry ltered and the solvent removed

(twice more) to leave the dioxadisiladecane (15) (1 561 g, 99%).

(2 S,4 S)-4-(Methoxymethyl)-2-phenyl-1,3-dioxan (19)

2957, 2869, 1391, 1251 (Si–C), 1096, 1031, 842 (Si–C),

(^A) The oil was removed from NaH (50% dispersion; 163 mg,

3 4 mmol) with hexanes, then tetrahydrofuran (10 0 ml) was

added. A solution of dioxan (5) (0 330 g, 1 70 mmol) and

imidazole (11 mg, 0 16 mmol) in tetrahydrofuran (5 0 ml) was

added dropwise, and the reaction mixture re uxed for 1 h.

After cooling the mixture to room temperature, MeI (0 28 ml,

4 5 mmol) was added and the reaction mixture stirred for

1 h before methanol (3 ml) was added. The solvents were

removed and the residue was dissolved in CH₂Cl₂and worked

up. Flash chromatography (hexanes/Et₂O, 4 : 1) gave the

(methoxymethyl)dioxan (19) as a yellow oil (166 mg, 47%).

max

1

749, 685 cm

.

0 30 (s) and 0 31 (s, SiMe₃); 1 68–2 03 (m,

H

(H 6)₂); 3 62–3 68 (dd, J 5 6, 1 6 Hz, (H 4)₂); 3 80–3 89 (dd,

J 7 4, 5 9 Hz, (H 7)₂); 3 96–4 09 (dtd, J 8 2, 5 6, 4 0 Hz,

H 5).

or C 7); 70 2 (C 5).

0 3 (SiMe₃); 37 0 (C 6); 59 0 (C 4 or C 7); 67 1 (C 4

C

Tricarbonyl[(dimethoxymethyl)- ⁶-benzene]chromium (18)

(Dimethoxymethyl)benzene (4) (1 00 ml, 6 67 mmol) and

Cr(CO)₆(1 944 g, 8 84 mmol) were re uxed in Bu₂O (36 0 ml)

and tetrahydrofuran (4 0 ml) under a ow of N₂for 29 h. The

cooled solution was ltered and the solvents were removed.

Flash chromatography (hexanes/Et₂O, 4 : 1) gave the tricar-

bonyl chromium complex (18) (0 910 g, 47%) as a yellow

oil which solidi ed on standing overnight, m.p. 37 5–39 5 C.

2925, 2858, 1454, 1376, 1244, 1145, 1103, 1026, 996, 755,

max

1

699 cm

.

1 47–1 60 (d, J 13 3 Hz, H 5eq); 1 76–1 98

H

(qd, J 12 3, 5 1 Hz, H 5ax); 3 41 (s, OMe); 3 35–3 63 (m,

CH₂OMe); 3 90–4 06 (td, J 11 8, 2 7 Hz, H 6ax); 4 03–4 16

(m, H 4ax); 4 23–4 34 (ddd, J 11 4, 5 1, 1 4 Hz, H 6eq); 5 53

2939, 2835, 1965 and 1876 (CO), 1455, 1201, 1106, 1055,

max

(s, H 2); 7 30–7 38 (m, Hm, Hp); 7 46–7 53 (m, Ho).

27 9

C

1

663, 630, 535 cm

.

3 39 (s, OMe); 5 12 (s, Ph–CH);

H

(C 5); 59 4 (OMe); 66 8 (C 6); 75 6 (C 4); 76 2 (CH₂OMe);

101 3 (C 2); 126 2 (Co or Cm); 128 2 (Co or Cm); 128 7 (Cp);

138 2 (Cipso). G.c.–m.s. (130 C for 35 min, 10 C per min to

250 C, 250 C for 15 min): 22 88 min [1%; m/z 208 (14%, M⁺),

207 (47, M H), 105 (55, PhCO⁺), 91 (25, PhCH₂⁺), 45 (100,

CH₃O⁺=CH₂), 44 (69, CH₂O⁺=CH₂); due to dioxolan]; 25 09

min [99%; m/z 208 (25%), 207 (18), 163 (100, M⁺C₂H₅O),

105 (59), 91 (46), 77 (44, Ph⁺), 45 (33)].

(^B) Alcohol (5) (0 724 g, 3 73 mmol) was dissolved in

dry dimethyl sulfoxide (6 0 ml). Powdered KOH (0 25 g,

4 46 mmol) was added to the stirred solution; after 30 min,

MeI (1 3 ml, 21 mmol) was added and the solution was stirred

for 19 h. The reaction mixture was then poured into water

and extracted with Et₂O. Workup and ash chromatography

(hexanes/Et₂O, 1 : 1) gave (i) (19) (44 mg, 6%); and (ii) starting

material (100 mg, 14%).

5 24–5 40 (m, Hm, Hp); 5 47–5 56 (d, J 5 7 Hz, Ho).

C

53 3 (OMe); 91 2 (Co or Cm); 91 9 (Co or Cm); 92 2 (Cp);

101 3 (Ph–CH); 107 2 (Cipso); 232 4 (Cr(CO)₃).

Tricarbonyl[(2 S,4 S)-2-( ⁶-phenyl)-1,3-dioxan-4-

methanol]chromium (16)

(^A) (2S,4S)-2-Phenyl-1,3-dioxan-4-methanol (5) (196 mg,

1 01 mmol) and Cr(CO)₆(0 258 g, 1 17 mmol) were re uxed

in Bu₂O (9 0 ml) and tetrahydrofuran (1 0 ml) under a ow

of N₂for 24 h. The cooled solution was ltered and the

solvents were removed. Flash chromatography (hexanes/Et₂O,

1 : 2) three times (unresolved fractions were put back onto

the column) gave tricarbonylchromium complex (16) (140 mg,

42%) as a thick yellow oil which solidi ed after standing

for 1 month, m.p. 77 0–79 0 C (Found: M⁺, 330 0198.

(^C) Alcohol (5) (105 mg, 0 541 mmol) was dissolved in dry

C

₁₄H₁₄CrO₆requires M⁺, 330 0196). m/z 330 (18%, M⁺);

274 (24, M 2CO); 246 (51, M 3CO); 174 (56); 158 (37); 91

(27, PhCH₂⁺); 52 (100, Cr⁺).

3419 (OH), 2866, 1964

and 1876 (CO), 1361, 1104, 1024, 660 cm

tetrahydrofuran (2 0 ml) and cooled to 78 C. BuLi (1 80 mol

1

l

in hexanes, 0 29 ml, 0 52 mmol) was added and the solu-

max

1

tion stirred for 10 min before MeI (0 06 ml, 0 96 mmol) was

added. After 1 h the mixture was warmed to room temperature.

Methanol (4 drops) was added and the solution diluted with

CH₂Cl₂. Workup returned starting material (98 mg).

.

1 42–1 47

H

(d, J 13 3 Hz, H 5eq); 1 83–1 96 (qd, J 12 5, 5 2 Hz, H 5ax);

2 25 (br s, OH); 3 63–3 76 (m, CH₂OH); 3 88–3 96 (td, J

12 0, 2 6 Hz, H 6ax); 3 96–4 04 (m, H 4ax); 4 24–4 29 (ddd,

J 11 4, 5 1, 1 0 Hz, H 6eq); 5 22 (s, H 2); 5 25–5 44 (m, Hm,

(^D) Alcohol (5) (95 mg, 0 49 mmol) was dissolved in Et₂O

(0 5 ml). Tetrabutylammonium iodide (2 mg, 0 005 mmol)

was added followed by a solution of NaOH (79 mg, 2 0 mmol)

in water (0 1 ml). The mixture was stirred for 20 min and

the ask was then cooled in ice–water. Me₂SO₄(0 10 ml,

1 1 mmol; ltered through K₂CO₃) was added carefully. After

6 h, concentrated aqueous ammonia (2 drops) was added; more

water and Et₂O were added after a further 30 min. Workup

and ash chromatography (hexanes/Et₂O, 4 : 1) gave (i) (19)

(33 mg, 32%); and (ii) starting material (20 mg, 21%).

(^E) The oil was removed from KH (24% dispersion; 0 81 g,

4 9 mmol) with hexanes, then tetrahydrofuran (3 0 ml) was

added, followed by alcohol (5) (59 mg, 0 30 mmol). The

mixture was stirred at room temperature for 2 h before MeI

(0 20 ml, 3 2 mmol) was added. After the mixture was stirred

overnight methanol (5 drops) was added, followed by CH₂Cl₂.

Workup gave (19) (36 mg, 57%).

Hp); 5 45–5 68 (m, Ho).

26 4 (C 5); 65 5 (CH₂OH); 66 6

C

(C 6); 77 7 (C 4); 91 3 (Co or Cm); 91 4 (Co or Cm); 92 7

(Cp); 98 3 (C 2); 107 6 (Cipso); 232 7 (Cr(CO)₃).

(^B) A solution (1 0 ml) of trimethylsilyl tri uoromethane-

sulfonate (0 05 ml, 0 26 mmol) in dry CH₂Cl₂(10 0 ml)

was cooled to 42 C. (The dioxadisiladecane (15) (143 mg,

0 444 mmol) was added followed by a solution of [(1,2,3,4,5,6-

)benzaldehyde]tricarbonylchromium (17) (109 mg, 0 450

mmol) in CH₂Cl₂(1 0 ml). The solution was stirred for 3 5 h

and then the temperature was raised to 23 C for 3 h. Et₃N

(3 drops) was added and the mixture was warmed to room tem-

perature. Workup and ash chromatography (hexanes/Et₂O,

1 : 2) gave the following. (i) Starting complex (17) (19 mg,

17%) was obtained as an orange oil.

1

1966 and 1886 (CO),

1694 cm (C=O). (ii) The tricarbonylchromium complex (16)

was obtained as a yellow oil (74 mg, 51%).

max

Functionalization of Complexes of Tricarbonylchromium

1091

Methyl (2 S,4 S)-2-Phenyl-1,3-dioxan-4-ylmethyl Carbonate

(20)

(ddd, J 11 9, 4 9, 1 4 Hz, H 6eq); 5 52 (s, H 2); 7 31–7 38

(m, Hm, Hp); 7 45–7 53 (m, Ho).

0 1 (SiMe₂); 18 3

C

(SiCMe₃); 25 9 (SiCMe₃); 28 3 (C 5); 66 2 (C 6 or CH₂OSi);

66 9 (C 6 or CH₂OSi); 77 6 (C 4); 101 1 (C 2); 126 1 (Co or

Cm); 128 1 (Co or Cm); 128 7 (Cp); 138 6 (Cipso).

The alcohol (5) (54 mg, 0 28 mmol) was dissolved in dry

dimethylformamide (3 0 ml). MeI (0 07 ml, 1 1 mmol) was

added, followed by Ag₂O (unknown age; 0 204 g, 0 88 mmol).

The mixture was stirred at room temperature for 45 h. Chlo-

roform was added, and the solution was washed twice with

5% aqueous potassium cyanide, three times with water, then

brine, and dried. Flash chromatography (hexanes/Et₂O, 4 : 1)

gave the carbonate (20) (26 mg, 37%) (Found: M⁺, 252 0991.

Tricarbonyl[(2 S,4 S)-4-(methoxymethyl)-2-( ⁶-phenyl)-1,3-

dioxan]chromium (23)

The dioxan (19) (144 mg, 0 692 mmol) and Cr(CO)₆

(0 220 g, 1 00 mmol) were re uxed in Bu₂O (9 0 ml) and

tetrahydrofuran (1 0 ml) under a ow of N₂for 16 h. The

cooled solution was ltered and the solvents were removed.

Flash chromatography (hexanes/Et₂O, 2 : 1) gave the following

compounds. (i) Starting material (21 mg, 15%). (ii) The

tricarbonylchromium complex (23) was obtained as a yellow oil

(138 mg, 58%) (Found: M⁺, 344 0349. C₁₅H₁₆CrO₆requires

M⁺, 344 0352). m/z 344 (12%, M⁺); 288 (24, M 2CO);

260 (58, M 3CO); 202 (33); 158 (84); 126 (41); 96 (29); 52

C

₁₃H₁₆O₅requires M⁺, 252 0998). m/z 252 (32%, M⁺); 251

(25, M H); 221 (10, M OMe); 163 (26, M CH₂OCOOMe);

105 (100, PhCO⁺); 91 (31, PhCH₂⁺); 77 (41, Ph⁺); 71 (41).

2958, 28559, 1749 (C=O), 1444, 1273 (C–O), 1105, 995,

max

1

700 cm

.

1 49–1 61 (d, J 13 2 Hz, H 5eq); 1 78–2 02

H

(qd, J 12 1, 5 1 Hz, H 5ax); 3 79 (s, OMe); 3 91–4 06 (td, J

11 9, 2 6 Hz, H 6ax); 4 10–4 37 (m, H 4ax, H 6eq, 4-CH₂O);

5 53 (s, H 2); 7 32–7 39 (m, Hm, Hp); 7 45–7 53 (m, Ho).

(100, Cr⁺).

1032, 737, 660, 629, 530 cm

2929, 2869, 1964 and 1875 (CO), 1363, 1101,

max

27 3 (C 5); 54 9 (OMe); 66 4 (C 6 or 4-CH₂O); 69 8 (C 6

or 4-CH₂O); 74 5 (C 4); 101 1 (C 2); 126 1 (Co or Cm); 128 2

(Co or Cm); 128 8 (Cp); 138 1 (Cipso).

C

1

.

1 45–1 61 (d, J 12 0 Hz,

H

H 5eq); 1 69–1 95 (m, H 5ax); 3 35–3 65 (m including 3 41,

s, OMe, CH₂OMe); 3 82–4 15 (m, H 4ax, H 6ax); 4 15–4 37

(m, H 6eq); 5 12–5 45 (m, H 2, Hm, Hp); 5 47–5 65 (m, Ho).

(2 S,4 S)-4-(Methoxymethoxymethyl)-2-phenyl-1,3-dioxan

(21)

27 5 (C 5); 59 5 (OMe); 66 8 (C 6); 75 1 (C 4); 76 3

C

(CH₂OMe); 91 0 (Ph); 91 3 (Ph); 91 5 (Ph); 91 6 (Ph); 92 2

(Ph); 98 2 (C 2); 106 5 (Cipso); 232 5 (Cr(CO)₃).

(^A) A solution of the alcohol (5) (80 mg, 0 41 mmol) in

Prⁱ₂NEt (1 0 ml, 5 8 mmol) was stirred at 0 C for 1 5 h.

BrCH₂OCH₃(0 05 ml, 0 61 mmol) was added dropwise, and

the ice bath was removed after 1 h. After stirring at room

temperature for 16 h, the mixture was poured onto ice–water

and extracted into Et₂O. Workup and ash chromatography

(hexanes/Et₂O, 1 : 1) gave the following compounds. (i) Ben-

zaldehyde (13 mg, 30%). (ii) Starting material (18 mg, 23%).

Tricarbonyl{(2 S,4 S)-4-[(t-butyldimethylsilyl)oxy]methyl-2-

(

⁶-phenyl)-1,3-dioxan}chromium (24)

The dioxan (22) (47 mg, 0 15 mmol) and Cr(CO)₆(53 mg,

0 24 mmol) were re uxed in Bu₂O (9 0 ml) and tetrahydro-

furan (1 0 ml) under a ow of N₂for 23 h. The cooled

mixture was ltered through Celite and the solvents were

removed. Flash chromatography (hexanes/Et₂O, 1 : 1) gave

the tricarbonylchromium complex (24) as a yellow oil (39 mg,

(iii) The ether (21) (15 mg, 15%).

1

2927, 1455, 1142, 1109,

1 47–1 65 (d, J 13 2 Hz, H 5eq);

H

max

1043, 755, 699 cm

.

1 79–2 03 (qd, J 12 2, 5 2 Hz, H 5ax); 3 38 (s, OMe); 3 53–

3 80 (m, 4-CH₂O); 3 91–4 07 (td, J 11 9, 2 4 Hz, H 6ax);

4 07–4 18 (m, H 4ax); 4 23–4 39 (ddd, J 11 4, 5 2, 1 4 Hz,

H 6eq); 4 68 (s, OCH₂OMe); 5 54 (s, H 2); 7 25–7 41 (m,

Hm, Hp); 7 45–7 54 (m, Ho).

(^B) Oven-dried K₂CO₃(82 mg, 0 59 mmol) was added to a

solution of the alcohol (5) (98 mg, 0 51 mmol) and 18-crown-6

(3 mg, 0 01 mmol) in dry toluene (0 50 ml). BrCH₂OCH₃

(0 05 ml, 0 61 mmol) was added to the stirred solution, which

was re uxed for 2 h. A large amount of benzaldehyde had

formed (t.l.c.).

58%) (Found: M⁺, 444 1071. C₂₀H₂₈CrO₆Si requires M⁺

444 1060). m/z 444 (12%, M⁺), 360 (100, M 3CO), 317

(39), 275 (49), 169 (59), 126 (31), 52 (51, Cr⁺).

2929,

2857, 1971 and 1888 (CO), 1472, 1362, 1254 (Si–C), 1110,

,

max

1

838 (Si–C), 778, 659, 629 cm

.

0 08 (s, SiMe₂); 0 90 (s,

H

Bu^tSi); 1 52–1 94 (m, H 5eq, H 5ax); 3 54–4 00 (m, CH₂OSi,

H 4ax, H 6ax); 4 19–4 33 (dd, J 11 1, 4 4 Hz, H 6eq); 5 24 (s,

H 2); 5 26–5 38 (m, Hm, Hp); 5 47–5 59 (d, J 5 8 Hz, Ho).

2 6 (SiMe₂); 18 3 (SiCMe₃); 25 9 (SiCMe₃); 27 8 (C 5);

C

65 9 (CH₂OSi or C 6); 66 9 (CH₂OSi or C 6); 77 7 (C 4); 90 8

(Co or Cm); 91 8 (Co or Cm); 91 9 (Cp); 98 2 (C 2); 108 0

(Cipso); 232 5 (Cr(CO)₃).

(^C) Alcohol (5) (105 mg, 0 541 mmol) and p-TsOH (3 mg,

0 015 mmol) were dissolved in CH₂(OMe)₂(2 0 ml, 23 mmol)

and the solution was stirred overnight. A large amount of

benzaldehyde had formed (t.l.c.).

Deprotonation and D₂O Quench of Tricarbonyl[(2 S,4 S)-2-

(

⁶-phenyl)-1,3-dioxan-4-methanol]chromium (16)

(2 S,4 S)-4-[(t-Butyldimethylsilyl)oxy]methyl-2-phenyl-1,3-

dioxan (22)

(^A) The tricarbonylchromium complex (16) (44 mg, 0 13

mmol) was dissolved in dry tetrahydrofuran (1 0 ml) in a

The alcohol (5) (98 mg, 0 51 mmol) was dissolved in dry

ame-dried and nitrogen- ushed ask, and the solution was

1

CH₂Cl₂(1 0 ml), and

a

solution of Bu^tMe₂SiCl (96 mg,

cooled to 78 C. Bu^tLi (1 45 mol l

in hexanes; 0 33 ml,

0 64 mmol) and 1,8-diazabicyclo[5.4.0]undec-7-ene (0 09 ml,

0 60 mmol) in dry CH₂Cl₂(1 0 ml) was added. The mixture

was stirred for 18 h before it was diluted with CH₂Cl₂and

0 48 mmol) was added, followed 10 min later by D₂O (0 10 ml,

5 5 mmol). The solution was warmed to room temperature

over 3 h. The solution was dried, ltered through Celite and

the solvent removed to leave an oil which was dissolved in

Et₂O and exposed to air and sunlight for 1 h. The mixture

was ltered and the solvent removed to leave a pale yellow oil

(27 mg, 100%). m/z 250 (2%), 198 (2), 197 (10), 196 (30), 195

(58), 194 (54), 193 (186), 167 (3), 166 (14), 165 (42), 164 (64),

163 (19), 110 (9), 109 (29), 108 (59), 107 (66), 106 (77), 105

washed quickly with small portions of ice-cold water, 0 25 mol

1

l

HCl and saturated aqueous NaHCO₃. Solvent removal and

ash chromatography (hexanes/Et₂O, 1 : 1) gave the following

compounds. (i) Starting material (18 mg, 18%). (ii) The

silyl ether (22) (70 mg, 45%) was also isolated (Found: M⁺

308 1792.

₁₇H₂₈O₃Si requires M⁺, 308 1808). m/z 251

(27%, M Bu^t); 145 (100, ⁺CH₂OSiMe₂Bu^t); 117 (49); 105

(28, PhCO⁺); 91 (94, PhCH₂⁺); 75 (56); 59 (29).

2929,

2856, 1462, 1255 (Si–C), 1111, 1027, 837 (Si–C), 778, 697 cm

0 07 (s, SiMe₂); 0 91 (s, Bu^tSi); 1 57–1 69 (d, J 11 7 Hz,

,

C

(27), 92 (46), 80 (61), 71 (100), 57 (55).

1

3416 (OH), 2958,

1 22–2 15 (m, H 5eq,

H

max

2865, 1364, 1104, 1024, 634 cm

.

max

1

.

H 5ax); 3 60–4 23 (m, CH₂OH, H 4ax, H 6ax); 4 23–4 39 (m,

H 6eq); 5 55 (s, 0 6H, H 2); 7 27–7 58 (m, Ph–H).

H

H 5eq); 1 71–1 88 (qd, J 13 2, 5 0 Hz, H 5ax); 3 76–3 81 (d,

J 5 3 Hz, CH₂OSi); 3 86–4 04 (m, H 4ax, H 6ax); 4 25–4 36

(^B) The complex (16) (42 mg, 0 13 mmol) was dissolved in

tetrahydrofuran (1 0 ml) in a ame-dried and nitrogen- ushed

1092

J. D. Kendall and P. D. Woodgate

1

ask and cooled to 78 C. BuLi (1 18 mol l

;

0 38 ml,

1 3 Hz, 0 4H); 4 04–4 12 (ddd, J 11 4, 5 1, 1 3 Hz, 0 8H);

4 39–4 43 (td, J 6 3, 1 1 Hz, 0 2H); 4 52–4 56 (t, J 6 4 Hz,

0 05H); 4 85–4 93 (td, J 6 5, 1 2 Hz, 0 3H); 5 05–5 13 (dd,

J 6 4, 1 1 Hz, 0 3H); 5 41 (s, 0 2H); 5 49 (s, 0 1H); 5 55 (s),

5 56 (s, total 0 1H); 5 64–5 68 (dd, J 6 8, 1 0 Hz, 0 2H); 5 81

(s, 0 3H); 7 20–7 32 (m including C₆H₆, 1 9H); 7 32–7 47

(td, J 7 5, 1 4 Hz, 0 4H); 7 53–7 56 (dt, J 7 3, 1 3 Hz);

7 62–7 67 (dd, J 7 4, 0 9 Hz, 0 4H); 7 78–7 87 (m, 0 3H);

0 45 mmol) was added, followed 20 min later by D₂O (0 05 ml,

2 8 mmol). The mixture was warmed to room temperature

over 2 h, dried, ltered through Celite and the solvent removed

to leave an orange oil (44 mg). This was dissolved in Et₂O

and exposed to sunlight. Filtration and removal of the solvent

a orded a colourless oil (21 mg, 85%). m/z 198 (1%), 197 (5),

196 (24), 195 (68), 194 (65), 193 (17), 167 (1), 166 (7), 165

(35), 164 (88), 163 (16), 110 (3), 109 (20), 108 (61), 107 (56),

8 18–8 22 (dd, J 7 8, 1 3 Hz, 0 2H).

(C₆D₆) 0 54;

C

106 (100), 105 (25), 92 (59), 80 (71), 78 (65), 71 (98), 57 (59).

0 35; 0 73; 0 83; 2 04; 27 56; 28 19; 65 44; 66 01; 66 17;

66 50; 66 63; 66 71; 66 77; 77 78; 77 90; 78 03; 89 20; 90 46;

94 55; 98 52; 99 78; 101 42; 126 74; 127 00; 129 34; 131 61;

134 45; 137 61; 144 96; 233 34; 233 60.

A solution of fraction (iii) in CH₂Cl₂was exposed to sunlight

for 4 h. Filtration through Celite and removal of the solvent

gave the alcohol (28) and the disilyl compound (30) (14 mg).

1

3417 (OH), 2956, 2861, 1363 8, 1104, 1023, 633 cm

.

max

1 39–1 50 (d, J 13 2 Hz, H 5eq); 1 85–2 03 (qd, J 11 7,

H

5 4 Hz, H 5ax); 3 68 (br s, CH₂OH); 3 87–4 05 (m, H 4ax,

H 6ax); 4 26–4 39 (ddd, J 11 4, 5 2, 1 2 Hz, H 6eq); 5 55 (s,

0 8H, H 2); 7 30–7 42 (m, Hm, Hp); 7 42–7 51 (m, 1 3H,

Ho).

(^C) The complex (16) (28 mg, 0 085 mmol) was dissolved in

dry Et₂O (1 5 ml) in a ame-dried and nitrogen- ushed ask,

and cooled to 42 C; BuLi (2 09 mol l ¹; 0 15 ml, 0 31 mmol)

was added. After 30 min D₂O (0 015 ml, 0 83 mmol) was

added to the yellow solution/precipitate. After 1 h, the mixture

was stirred at room temperature for 1 h before it was dried,

ltered through Celite, and the solvent removed to leave a

yellow-orange oil (27 mg). m/z 332 (3%), 331 (9), 330 (11),

275 (10), 274 (13), 247 (25), 246 (34), 175 (34), 174 (37), 159

3453 (OH), 2956, 1364, 1250 (Si–C), 1105, 839 (Si–C),

max

1

757 cm

.

(CDCl₃) 0 11 (s, 2 3H, OSiMe₃); 0 35 (s,

H

CSiMe₃); 1 41–1 53 (d, J 13 2 Hz, H 5eq); 1 86–2 08 (m,

H 5ax); 3 63–4 06 (m, CH₂OH, H 4ax, H 6ax); 4 25–4 35 (ddd,

J 11 3, 5 1, 1 4 Hz, 1H, H 6eq); 5 72, (s, H 2); 7 28–7 55 (m,

3H, Ph–H); 7 68–7 75 (d, J 7 6 Hz, Ph–H).

(CDCl₃) 0 6

C

(SiMe₃); 26 7 (C 5); 65 7 (CH₂OH and CH₂OSi, or C 6); 66 5

(CH₂OH and CH₂OSi, or C 6); 77 6 (C 4); 101 0 (C 2); 126 2

(Ph); 128 3 (Ph); 129 4 (Ph); 134 2 (Ph).

(^B) The complex (16) (110 mg, 0 333 mmol) was dissolved in

dry Et₂O (2 0 ml) in a ame-dried and nitrogen- ushed ask,

and cooled to 78 C. BuLi (1 18 mol l ¹; 1 00 ml, 1 18 mmol)

was added slowly. After 1 h Me₃SiCl (0 20 ml, 1 57 mmol)

was added, and the mixture was stirred for 1 h before warming

to room temperature. Saturated aqueous NaHCO₃(10 drops)

was added. Workup and ash chromatography (hexanes/Et₂O,

(16), 158 (29), 157 (17), 112 (24), 52 (100, Cr⁺).

(OH), 2928, 1965 and 1866 (CO), 1361, 1105, 1026, 666, 631,

3396

max

1

534 cm

.

1 20–1 69 (d, J 13 1 Hz, H 5eq); 1 75–2 08

H

(m, H 5ax); 2 23 (br s, OH); 3 58–4 09 (m, CH₂OH, H 4ax,

H 6ax); 4 19–4 35 (m, H 6eq); 5 22 (s, 0 9H, H 2); 5 24–5 43

(m, Hm, Hp); 5 45–5 68 (m, 1 6H, Ho).

4 : 1) gave compounds (27)–(30) as a yellow oil (32 mg).

max

Deprotonation and Me₃SiCl Quench of Tricarbonyl[(2 S,4S)-2-

(

1

1966 and 1888 (CO), 1251 (Si–C), 1109, 841 cm

(Si–C).

⁶-phenyl)-1,3-dioxan-4-methanol]chromium (16)

H

0 10 (s, 17H); 0 38 (s, 13H); 1 13–1 28 (t, J 7 0 Hz, 1 6H);

1 50–1 95 (m, 3 5H); 3 40–4 08 (m, 7 6H); 4 21–4 39 (m,

1 1H); 5 08–5 19 (m, 0 5H); 5 33 (s, 0 7H); 5 37–5 48 (m,

(^A) The complex (16) (82 mg, 0 25 mmol) was dissolved in

dry tetrahydrofuran (2 0 ml) in a ame-dried and nitrogen-

1

ushed ask, and cooled to 78 C. BuLi (1 18 mol l

;

0 8H); 5 50–5 70 (m, 2 0H); 7 30–7 50 (m, 2 0H).

0 57;

C

0 74 ml, 0 87 mmol) was added, and the yellow solution

stirred for 1 h before Me₃SiCl (0 14 ml, 1 1 mmol) was added.

The mixture was warmed slowly to room temperature over

1 5 h. Saturated aqueous NaHCO₃(3 drops) was added to

the brown solution, which was dried, ltered, and the solvent

removed. Flash chromatography (hexanes/Et₂O, 4 : 1) gave the

following fractions. (i) Tricarbonyl{(2S,4S)-2-( ⁶-phenyl)-4-

[(trimethylsilyl)oxy]methyl-1,3-dioxan}chromium (25) and

(2S,4S)-2-phenyl-4-[(trimethylsilyl)oxy]methyl-1,3-dioxan (26)

0 64; 27 69; 28 11; 65 17; 65 64; 66 59; 66 79; 77 57; 77 98;

88 98; 90 39; 94 78; 98 19; 99 96; 100 95; 101 19; 126 10;

128 16; 128 72; 129 29; 134 17; 233 05 (Cr(CO)₃).

A solution of the yellow oil in CH₂Cl₂was exposed to the

sunlight for 3 h until the yellow colour had disappeared. Filtra-

tion through Celite and removal of the solvent gave a mixture

of (28) and (30) as a colourless oil (15 mg) (Found: MH⁺

,

339 1823.

MH⁺, 267 1427. C₁₄H₂₃O₃Si requires MH⁺, 267 1416).

m/z 339 (16%), 267 (100), 235 (18), 163 (84). 3486,

2957, 1372, 1250 (Si–C), 1107, 839 (Si–C), 757 cm

C

₁₇H₃₁O₃Si₂requires MH⁺, 339 1812. Found:

(15 mg, 15%).

0 13 (s, 9H, OSiMe₃); 1 20–1 85 (m,

H

max

1

H 5eq, H 5ax); 3 55–4 07 (m, CH₂OSi, H 4ax, H 6ax); 4 18–

4 36 (m, H 6eq); 5 20–5 38 (m, 2 8H, H 2, Hm, Hp);

.

H

0 11 (s), 0 12 (s), 0 14 (s, total 11H); 0 34 (s, 4 4H); 0 35

(s, 5 6H); 0 82–0 98 (m, 0 6H); 1 39–1 54 (d, J 13 2 Hz,

0 9H); 1 55–2 09 (m, 4 0H); 3 52–3 83 (m, 3 1H); 3 87–4 06

(m, 2 6H); 4 22–4 36 (m, 1 1H); 5 52 (s, 0 1H); 5 55 (s,

0 1H); 5 67 (s, 0 4H); 5 72 (s, 0 3H); 7 28–7 43 (m, 3 1H);

7 44–7 55 (m, 1 8H); 7 68–7 76 (d, J 7 7 Hz, 0 7H). G.c.

(180 C for 20 min, 10 C per min up to 250 C, 250 C for

15 min): 4 67 min {21%; due to dioxan (30)}; 11 76 min {79%;

due to dioxan (28)}.

5 48–5 61 (d,

J

5 9 Hz, 1 5H, Ph–H); 7 28–7 55 (m,

1 7H, Ph–H). (ii) Tricarbonyl{(2S,4S)-2-[2-(trimethylsilyl)-

⁶-phenyl]-1,3-dioxan-4-methanol}chromium (27) and (2S,4S)-

2-[2-(trimethylsilyl)phenyl]-1,3-dioxan-4-methanol (28) (10 mg,

10%).

0 35 (s) and 0 38 (s, SiMe₃); 1 10–2 05 (m, H 5ax,

H

H 5eq); 3 48–4 13 (m, CH₂OH, H 4ax, H 6ax); 4 13–4 41

(m, H 6eq); 5 15–5 75 (m, 2 6H, H 2, Cr–Ph–H); 7 28–7 53

(m, 2 4H, Ph–H). (iii) A mixture of tricarbonyl{(2S,4S)-4-

[(trimethylsilyl)oxy]methyl-2-[2-(trimethylsilyl)- ⁶-phenyl]-1,3-

dioxan}chromium (29) and (2S,4S)-4-[(trimethylsilyl)oxy]-

methyl-2-[2-(trimethylsilyl)phenyl]-1,3-dioxan (30) (47 mg)

Deprotonation and MeI Quench of Tricarbonyl[(2 S,4 S)-2-

(

⁶-phenyl)-1,3-dioxan-4-methanol]chromium (16)

(Found: M⁺

, ,

474 0986. C₂₀H₃₀CrO₆Si₂requires M⁺

474 0990. Found: M⁺, 402 0586. C₁₇H₂₂CrO₆Si requires

(^A) The complex (16) (76 mg, 0 23 mmol) was dissolved in

M⁺, 402 0591). m/z 474 (1), 402 (32), 318 (78), 214 (37),

163 (100), 126 (33), 73 (17, ⁺SiMe₃), 52 (83, Cr⁺).

dry Et₂O (2 0 ml) in a ame-dried and nitrogen- ushed ask,

and cooled to 78 C. BuLi (1 18 mol l ¹, 0 69 ml, 0 81 mmol)

was added, and the solution stirred for 1 h. MeI (0 065 ml,

1 04 mmol) was then added and the reaction mixture slowly

warmed to room temperature over 2 h. Saturated aqueous

NaHCO₃(3 drops) was added, and the solution dried, ltered

through Celite, and the solvent removed to leave starting

2955,

1

max

1966 and 1888 (CO), 1250 (Si–C), 1108, 841 (Si–C), 626 cm

.

(C₆D₆) 0 15 (s), 0 20 (s), 0 22 (s, total 9H); 0 32 (s),

H

0 43 (s), 0 46 (s, total 9H); 0 98–1 06 (d, J 13 2 Hz, 0 7H);

1 16–1 29 (m, 0 9H); 1 57–1 93 (m, 1 8H); 3 58–3 72 (m,

2 3H); 3 77–3 88 (m, 1 2H); 3 95–4 02 (ddd, J 11 6, 5 2,

Functionalization of Complexes of Tricarbonylchromium

1093

material (16) (87%) and decomplexed starting material (5)

(13%) as a yellow oil (77 mg).

(^C) The complex (16) (104 mg, 0 32 mmol) was dissolved in

dry Et₂O (2 0 ml) in a ame-dried and nitrogen- ushed ask,

and cooled to 78 C. BuLi (1 18 mol l ¹; 0 94 ml, 1 1 mmol)

was added, and after 10 min, the temperature was raised to

23 C for 1 h. MeOTf (0 16 ml, 1 4 mmol) was added, and

the mixture was slowly warmed to room temperature over 2 h.

Saturated aqueous NaHCO₃(3 drops) was added. Workup

and ash chromatography (hexanes/CH₂Cl₂, 1 : 2) gave the

following compounds. (i) The benzaldehyde (17) (38 mg, 49%).

(ii) Starting material (16) (4 mg, 4%). (iii) A mixture of

compound (17) and tricarbonyl{(2S,4S)-4-(methoxymethyl)-2-

(2-methyl- ⁶-phenyl)-1,3-dioxan}chromium (31) was obtained

(^B) The complex (16) (56 mg, 0 17 mmol) was dissolved

in dry Et₂O (1 0 ml) in a ame-dried and nitrogen- ushed

ask, and cooled to 78 C. BuLi (1 18 mol l ¹; 0 51 ml,

0 60 mmol) was added. The temperature was raised to 0 C

after 15 min. After a further 1 5 h, the yellow precipitate was

cooled again to 78 C. MeI (0 12 ml, 1 91 mmol) was added

and the reaction mixture warmed slowly to room temperature

over 2 h. Saturated aqueous NaHCO₃(3 drops) was added.

Workup gave starting material (16) (26%) and decomplexed

starting material (5) (74%) as a yellow oil (46 mg).

(^C) The complex (16) (55 mg, 0 17 mmol) was dissolved in

dry Et₂O (1 0 ml) in a ame-dried and nitrogen- ushed ask,

and cooled to 78 C. BuLi (1 18 mol l ¹; 0 49 ml, 0 58 mmol)

was added, producing a yellow precipitate which was stirred

for 30 min before CuBr.SMe₂(121 mg, 0 59 mmol) was added.

After a further 30 min, MeI (0 10 ml, 1 6 mmol) was added.

The precipitate became brown and the mixture was warmed

to room temperature over 4 h. Saturated aqueous NaHCO₃

(3 drops) was added. Workup gave the starting material (16)

(83%) and decomplexed starting material (5) (17%) as a yellow

oil (75 mg).

(^D) The complex (16) (100 mg, 0 30 mmol) was dissolved

in dry Et₂O (2 0 ml) in a ame-dried and nitrogen- ushed

ask, and cooled to 78 C. Bu^tLi (1 45 mol l ¹; 0 73 ml,

1 1 mmol) was added. After 5 min, MeI (0 20 ml, 3 2 mmol)

was added and the reaction mixture was warmed to room

temperature over 3 h. Saturated aqueous NaHCO₃(3 drops)

was added. Workup gave the starting material (16) (73%) and

decomplexed starting material (5) (27%) as a dark brown oil

(88 mg).

as an oil (39 mg).

1 48–1 60 (d, J 13 3 Hz, H 5eq); 1 77–

H

1 98 (qd, J 12 3, 5 1 Hz, H 5ax); 2 24 (s, 0 1H, Cr–PhMe);

2 39 (s, 0 3H, PhMe); 3 33–3 64 (m including 3 41, s, OMe,

CH₂OMe); 3 91–4 15 (m, H 4ax, H 6ax); 4 24–4 37 (ddd, J

11 4, 5 2, 1 3 Hz, H 6eq); 5 22–5 33 (m, Cr–Ph–H); 5 52–5 63

(m, Cr–Ph–H); 7 12–7 22 (m, 0 3H, Ph–H); 7 29–7 40 (m,

1 7H, Ph–H); 7 46–7 52 (m, 0 1H, Ph–H).

Deprotonation and Me₃SiCl Quench of Tricarbonyl[(2 S,4 S)-

4-(methoxymethyl)-2-( ⁶-phenyl)-1,3-dioxan]chromium (23)

The tricarbonylchromium complex (23) (103 mg, 0 299

mmol) was dissolved in dry Et₂O (2 0 ml) in a ame-dried and

nitrogen- ushed ask, and cooled to 78 C. BuLi (1 18 mol

l

¹; 0 64 ml, 0 755 mmol) was added and the solution stirred

for 1 h. Me₃SiCl (0 14 ml, 1 1 mmol) was added, the reaction

mixture was warmed to room temperature over 2 h, and sat-

urated aqueous NaHCO₃(8 drops) was added. Workup and

ash chromatography (hexanes/Et₂O, 2 : 1) gave (i) decom-

plexed starting material (19) (16 mg, 26%); and (ii) starting

material (23) (13 mg, 13%).

Deprotonation and D₂O Quench of Tricarbonyl {(2 S,4 S)-4-

[(t-butyldimethylsilyl)oxy]methyl-2-( ⁶-phenyl)-1,3-dioxan}-

chromium (24)

Deprotonation and MeOTf Quench of Tricarbonyl[(2 S,4 S)-

2-( ⁶-phenyl)-1,3-dioxan-4-methanol]chromium (16)

The tricarbonylchromium complex (24) (12 mg, 0 027 mmol)

was dissolved in dry Et₂O (1 0 ml) in a ame-dried and

nitrogen- ushed ask, and cooled to 42 C. BuLi (2 09 mol

(^A) The complex (16) (99 mg, 0 30 mmol) was dissolved

in dry Et₂O (2 0 ml) in a ame-dried and nitrogen- ushed

ask, and cooled to 78 C. BuLi (1 18 mol l ¹; 0 89 ml,

1 05 mmol) was added, and the solution stirred for 1 h. MeOTf

(0 16 ml, 1 4 mmol) was added and the reaction mixture was

warmed to room temperature over 4 h before saturated aqueous

NaHCO₃(3 drops) was added. The solution was dried, ltered

through Celite and the solvent removed. Flash chromatography

(hexanes/CH₂Cl₂, 1 : 2) gave the following compounds. (i) The

tricarbonylchromium complex (17) (19 mg, 26%) was obtained

l

¹, 0 038 ml, 0 079 mmol) was added and the yellow solution

stirred for 30 min before D₂O (0 015 ml, 0 83 mmol) was

added. After 1 5 h, the reaction mixture was warmed to room

temperature for 1 h. Workup gave a yellow oil (11 mg). m/z

446 (5%), 445 (12), 444 (8), 361 (100), 360 (71), 318 (40), 317

(26), 276 (50), 275 (37), 169 (88), 127 (38), 126 (45), 52 (82,

Cr⁺).

838 (Si–C), 628 cm

2929, 1971 and 1893 (CO), 1255 (Si–C), 1110,

max

1

.

0 08 (s, SiMe₂); 0 90 (s, Bu^tSi);

H

as an orange oil.

1

2964, 1980 and 1908 (CO), 1698 (C=O),

5 21–5 32 (t, J 6 2 Hz, Hm); 5 63–5 70 (t, J

H

max

1 51–2 00 (m, H 5eq, H 5ax); 3 55–4 05 (m, CH₂OSi, H 4ax,

H 6ax); 4 21–4 39 (m, H 6eq); 5 24 (s, H 2); 5 26–5 37 (m,

Hm, Hp); 5 51–5 57 (m, 1 5H, Ho).

1337 cm

.

6 2 Hz, Hp); 5 89–5 95 (d, J 6 4 Hz, Ho); 9 46 (s, PhCHO).

(ii) The tricarbonyl chromium complex (23) was obtained as

a yellow oil (50 mg, 48%). (iii) Starting material (16) (12 mg,

12%).

(1,1-Dimethoxyethyl)benzene (32)

Acetophenone (1 325 g, 11 0 mmol), trimethyl orthofor-

mate (1 50 ml, 13 7 mmol) and p-TsOH (17 mg, 0 090 mmol)

were dissolved in methanol (30 ml) in a ask equipped with a

Vigreaux column. The solution was stirred and heated with

a Bunsen burner, and a colourless liquid distilled across at

60–65 C. K₂CO₃was added, and the solution was diluted

with CH₂Cl_2.Workup gave (1,1-dimethoxyethyl)benzene (32)

(^B) The complex (16) (60 mg, 0 17 mmol) was dissolved in

dry Et₂O (1 5 ml) in a ame-dried and nitrogen- ushed ask,

and cooled to 78 C. BuLi (1 18 mol l ¹; 0 37 ml, 0 44 mmol)

was added, producing a yellow precipitate. The temperature

was raised to 0 C after 5 min and the precipitate became brown.

After 1 h the mixture was cooled again to 78 C, then MeOTf

(0 10 ml, 0 85 mmol) was added. After the mixture was warmed

to room temperature over 3 h, saturated aqueous NaHCO₃

(3 drops) was added. Workup and ash chromatography

(hexanes/CH₂Cl₂, 2 : 1) gave the (methoxymethyl)dioxan (19)

and (2S,4S)-4-(methoxymethyl)-2-(2-methylphenyl)-1,3-dioxan

as a yellow liquid (1 825 g, 100%).

1448, 1276, 1147, 1092, 1042, 877, 765, 701 cm

C–CH₃); 3 19 (s, OMe); 7 26–7 39 (m, Hm, Hp); 7 46–7 53

(m, Ho). 26 0 (Me); 48 9 (OMe); 101 6 (Ph–C); 126 2

2991, 2942, 2830,

max

1

.

1 54 (s,

H

C

(Ho or Hm); 127 5 (Hp); 128 0 (Ho or Hm); 142 8 (Hipso).

[decomplexed (31)] as a pale yellow oil (13 mg).

1 48–1 60

H

(d, J 13 3 Hz, H 5eq); 1 77–1 98 (qd, J 12 3, 5 1 Hz, H 5ax);

2 39 (s, 0 7H, Ph–Me); 3 33–3 64 (m including 3 41, s, OMe,

CH₂OMe); 3 90–4 15 (m, H 4ax, H 6ax); 4 24–4 36 (ddd, J

11 4, 5 1, 1 3 Hz, H 6eq); 5 53 (s, H 2); 7 11–7 23 (m, Ph–H);

7 31–7 37 (m, Ph–H); 7 46–7 53 (m, 1 5H, Ph–H).

(2 S,4 S)-2-Methyl-2-phenyl-1,3-dioxan-4-methanol (33) and

Isomers (34)–(38)

(^A) (1,1-Dimethoxyethyl)benzene (32) (5 43 g, 32 7 mmol),

(S)-butane-1,2,4-triol (2) (3 00 ml, 33 7 mmol) and pyridinium

1094

J. D. Kendall and P. D. Woodgate

p-toluenesulfonate (1 spatula) were mixed in hexanes (50 ml)

and re uxed under a Dean–Stark separator for 5 h, until

1 2 ml of methanol had collected. The cooled solution was

diluted with CH₂Cl₂. Workup and ash chromatography

(hexanes/Et₂O, 1 : 1) gave a mixture of the dioxan (33) and

isomers (34)–(38) (3 315 g, 49%). (Found: MH⁺, 209 1176.

1 54 (s), 1 64 (s) and 1 67 (s), 7 4H); 2 30 (br s, 0 6H);

3 13–4 45 (m including 3 67–3 72 (dd, J 7 8, 6 3 Hz) and

4 18–4 22 (dd, J 8 3, 5 9 Hz), 6 3H); 7 26–7 51 (m, 5 0H).

Major product, 34%, one diastereoisomer of the dioxan (33)

or (34)

26 41 (C 5); 32 70 (2-Me); 60 65 (C 6 or CH₂OH);

C

65 98 (C 6 or CH₂OH); 70 67 (C 4); 100 96 (C 2); 126 74 (Co

or Cm); 127 64 (Cp); 128 75 (Co or Cm); 140 97 (Cipso).

Second major product, 33%, one diastereoisomer of the dioxolan

C

₁₂H₁₇O₃requires MH⁺, 209 1178). m/z 209 (26%, MH⁺),

193 (100, M Me), 131 (21), 121 (42), 105 (63, ⁺PhCO), 77

(18, Ph), 71 (53, C₄H₇O⁺).

3420 (OH), 2935, 1447,

1372, 1247, 1179, 1069, 1026, 765, 702 cm

(35) or (36)

28 27 (2-Me); 35 90 (4-CH₂); 60 38 (C 5 or

max

C

1

.

1 18–1 24

CH₂OH); 69 34 (C 5 or CH₂OH); 74 80 (C 4); 109 19 (C 2);

125 14 (Co or Cm); 127 82 (Cp); 128 18 (Co or Cm); 143 28

(Cipso). Third major product, 14%, other diastereoisomer of

H

(dtd, J 13 0, 2 4, 1 6 Hz, 0 2H); 1 50 (s), 1 52 (s), 1 53

(s, total 0 9H); 1 58–1 96 (m including 1 63 (s) and 1 66

(s), 5 0H); 2 28 (br s, 0 1H); 2 60 (br s, 0 4H); 2 70 (br s,

0 6H); 3 39–3 51 (t, J 8 3 Hz, 0 5H); 3 55–4 00 (m including

3 65–3 70 (dd, J 7 8, 6 4 Hz), 3 71–3 77 (t, J 5 8 Hz),

3 77–3 81 (t, J 5 4 Hz) and 3 86–3 90 (dd, J 7 8, 6 9 Hz),

4 0H); 4 06–4 13 (m, 0 4H); 4 15–4 21 (dd, J 8 2, 6 0 Hz,

0 5H); 4 33–4 42 (tdd, J 8 2, 5 8, 5 0 Hz, 0 4H); 7 23–7 51

(m, 5 0H). Major product, 41%, one diastereoisomer of (4S)-

the dioxolan (35) or (36)

28 16 (2-Me); 35 50 (4-CH₂);

C

60 50 (C 5 or CH₂OH); 69 86 (C 5 or CH₂OH); 75 72 (C 4);

109 23 (C 2); 125 00 (Co or Cm); 127 75 (Cp); 128 10 (Co

or Cm); 144 25 (Cipso). Other isomers

27 52 (Me); 28 34

C

(Me); 36 34 (CH₂); 36 76 (CH₂); 59 20 (CH₂); 59 38 (CH₂);

61 00 (CH₂); 69 54 (CH₂); 70 01 (CH); 70 87 (CH); 73 47

(CH); 125 20 (CH); 127 49 (CH); 127 99 (CH); 128 28 (CH);

128 54 (CH); 128 63 (CH); 128 95 (CH). G.c.–m.s. (150 C for

13 min, 5 C per min up to 250 C, 250 C for 15 min): 9 14 min

[34%; m/z 193 (65%), 131 (38), 105 (80), 77 (34), 71 (86), 43

(100); due to one diastereoisomer of the dioxan (33) or (34)];

10 02 min [33%; m/z 193 (82%), 105 (85), 77 (36), 71 (100),

43 (84); due to one diastereoisomer of the dioxolan (35) or

(36)]; 10 46 min [14%; m/z 193 (87%), 105 (95), 77 (40), 71

(100), 43 (76); due to other diastereoisomer of the dioxolan

(35) or (36)].

2-methyl-2-phenyl-1,3-dioxolan-4-ethanol (35) or (36)

28 05

C

(2-Me); 35 53 (4–CH₂); 60 03 (C 5 or CH₂OH); 69 76 (C 5

or CH₂OH); 75 35 (C 4); 109 09 (C 2); 124 91 (Co or Cm);

127 65 (Cp); 127 99 (Co or Cm); 144 18 (Cipso). Second

major product, 39%, other diastereoisomer of the dioxolan

(35) or (36)

28 17 (2-Me); 35 91 (4-CH₂); 59 97 (C 5 or

C

CH₂OH); 69 24 (C 5 or CH₂OH); 74 44 (C 4); 109 05 (C 2);

125 04 (Co or Cm); 127 71 (Cp); 128 08 (Co or Cm); 143 22

(Cipso). Third major product, 16 0%, one diastereoisomer of

(4S)-2-methyl-2-phenyl-1,3-dioxan-4-methanol (33) or (34)

C

26 41 (C 5); 32 60 (2-Me); 60 59 (C 6 or CH₂OH); 65 78 (C 6

or CH₂OH); 70 72 (C 4); 100 87 (C 2); 126 64 (Co or Cm);

127 55 (Cp); 128 66 (Co or Cm); 140 86 (Cipso). Minor

(2 S,4 S)-4-(Methoxymethyl)-2-methyl-2-phenyl-1,3-dioxan

(39) and Isomers (40)–(44)

isomers

26 97 (Me); 27 20 (Me); 37 37 (CH₂); 37 72

C

The oil was removed from NaH (50% dispersion; 55 mg,

1 1 mmol) with hexanes, then dry tetrahydrofuran (10 0 ml)

was added. A solution of the acetal mixture (33)–(38) (from

thermodynamic control; 111 mg, 0 534 mmol) and imidazole

(1 spatula) in dry tetrahydrofuran (5 0 ml) was added. The

mixture was re uxed for 1 h, cooled to room temperature, and

MeI (0 10 ml, 1 6 mmol) was added. After the mixture was

stirred overnight, methanol (1 ml) was added. Workup and

ash chromatography (hexanes/Et₂O, 1 : 1) gave compounds

(CH₂); 57 52 (CH₂); 58 68 (CH₂); 59 31 (CH₂); 65 27 (CH₂);

66 43 (CH₂); 67 77 (CH); 67 90 (CH); 69 69 (CH₂); 124 61

(CH); 125 53 (CH); 125 64 (CH); 127 50 (CH); 127 58 (CH);

127 89 (CH); 127 95 (CH). G.c.–m.s. (150 C for 10 min, 5 C

per min up to 250 C, 250 C for 15 min): 8 73 min [16%; m/z

193 (66%), 131 (41), 105 (82), 77 (34), 71 (88), 43 (100); due

to one diastereoisomer of the dioxan (33) or (34)]; 9 18 min

[3%; m/z 193 (65%), 121 (86), 105 (93), 77 (37), 71 (29), 43

(100); due to one diastereoisomer of (5S)-2-methyl-2-phenyl-

1,3-dioxepan-5-ol (37) or (38)]; 9 63 min [39%; m/z 193 (76%),

105 (81), 77 (32), 71 (100), 43 (82); due to one diastereoisomer

of (4S)-2-methyl-2-phenyl-1,3-dioxolan-4-ethanol (35) or (36)];

10 09 min [41%; m/z 193 (85%), 105 (99), 77 (35), 71 (100),

43 (73); due to other diastereoisomer of the dioxolan (35) or

(36)]; 10 78 min [1%; m/z 193 (70%), 121 (14), 105 (100),

77 (35), 71 (59), 43 (73); due to other diastereoisomer of the

dioxepan (37) or (38)].

(39)–(44) (61 mg, 52%).

1185, 1118, 1027, 882, 765, 702 cm

3060, 2987, 2875, 1448, 1371,

1

max

.

1 18–1 37 (m,

H

1 0H); 1 48–2 05 (m including 1 54 (s), 1 62 (s), 1 65 (s)

and 1 72 (s), 6 2H); 3 28–4 40 (m including 3 29 (s), 3 32

(s), 3 41 (s), 3 61–3 69 (dd, J 7 6, 6 5 Hz), 3 82–3 90 (dd, J

7 5, 6 6 Hz), 3 98–4 06 (t, J 6 3 Hz) and 4 12–4 20 (dd, J

8 2, 6 0 Hz), 7 6H); 7 24–7 50 (m, 5 0H).

27 44; 28 29;

C

28 30; 32 76; 33 54; 33 92; 58 67; 59 36; 60 90; 69 37; 69 46;

69 96; 73 61; 74 77; 76 00; 125 08; 125 18; 125 80; 126 80;

127 52; 127 62; 127 99; 128 09; 128 69. G.c.–m.s. (130 C for

20 min, 5 C per min up to 250 C, 250 C for 15 min): 7 75

min [19 0%; m/z 207 (77%), 177 (51), 145 (45), 105 (93), 85

(100), 71 (75), 45 (44), 43 (90); due to one diastereoisomer of

(4S)-4-(methoxymethyl)-2-methyl-2-phenyl-1,3-dioxan (39) or

(40)]; 7 85 min [33%; m/z 207 (89%), 145 (28), 105 (84),

77 (24), 45 (100), 43 (43); due to one diastereoisomer of

(4S)-4-(methoxyethyl)-2-methyl-2-phenyl-1,3-dioxolan (41) or

(42)]; 8 05 min [38%; m/z 207 (94), 145 (12), 105 (100), 77

(25), 45 (96), 43 (34); due to other diastereoisomer of (4S)-4-

(2-methoxyethyl)-2-methyl-2-phenyl-1,3-dioxolan (41) or (42)];

9 48 min [4%; m/z 207 (9%), 121 (21), 105 (24), 72 (100), 43

(23); due to one diastereoisomer of (5S)-5-methoxy-2-methyl-

2-phenyl-1,3-dioxepan (43) or (44)]; 9 56 min [4%; m/z 207

(8%), 121 (21), 105 (25), 72 (100), 43 (25); due to other

diastereoisomer of the dioxepan (43) or (44)]; 9 79 min [1%;

m/z 207 (65%), 177 (37), 105 (100), 85 (70), 71 (47), 45 (25),

43 (59); due to other diastereoisomer of the dioxan (39) or

(40)].

(^B) A solution (1 0 ml) of trimethylsilyl tri uoromethanesul-

fonate (0 01 ml, 0 052 mmol) in dry CH₂Cl₂(10 ml) was cooled

to 78 C. The dioxadisiladecane (15) (182 mg, 0 565 mmol)

was added followed by acetophenone (0 07 ml, 0 60 mmol).

After 7 h, pyridine (3 drops) was added and the solution warmed

to room temperature. Workup gave acetophenone (179 mg).

Repetition of this reaction at 42 C, or 42 to 20 to

10 C, gave acetophenone and a small amount of a mixture

of the dioxans/dioxolans/dioxepans (33)–(38).

(^C) A solution (1 0 ml) of trimethylsilyl tri uoromethanesul-

fonate (0 05 ml, 0 26 mmol) in dry CH₂Cl₂(10 0 ml) was cooled

to 42 C. The dioxadisiladecane (15) (156 mg, 0 484 mmol)

was added followed by (1,1-dimethoxyethyl)benzene (32) (87 mg,

0 524 mmol). After 5 h, the temperature was raised to 23 C

for 3 h. Pyridine (3 drops) was added and the reaction mixture

warmed to room temperature. Workup and ash chromato-

graphy (hexanes/Et₂O, 1 : 1) gave the dioxan (33) and isomers

(34)–(38) as a pale yellow oil (46 mg, 46%).

2954, 1447, 1372, 1251, 1184, 1070, 1029, 764, 703 cm

1 19–1 25 (d, J 12 9 Hz, 0 7H); 1 46–1 99 (m including

3453 (OH),

max

1

.

H

Functionalization of Complexes of Tricarbonylchromium

1095

Attempted Synthesis of (2 S,4 S)-4-(Methoxymethoxymethyl)-

2-methyl-2-phenyl-1,3-dioxan and Isomers

and the mixture was stirred for 20 h at room temperature.

Workup and ash chromatography (hexanes/Et₂O, 1 : 1) gave

the tricarbonylchromium complex and its isomers as a yellow

The oil was removed from NaH (50% dispersion; 58 mg,

1 2 mmol) with hexanes, and dry tetrahydrofuran (10 0 ml)

was added. A solution of the acetal mixture (33)–(38) (from

thermodynamic control; 118 mg, 0 567 mmol) and imidazole

(1 spatula) in dry tetrahydrofuran (5 0 ml) was added slowly.

The mixture was re uxed for 1 h and BrCH₂OCH₃(0 14 ml,

1 7 mmol) was added. After the mixture was stirred overnight,

methanol (1 ml) was added. Workup and ash chromatography

(hexanes/Et₂O, 9 : 1) gave (i) acetophenone (35 mg, 51%); and

(ii) starting material (48 mg, 41%).

oil (26 mg, 36%).

1256 (Si–C), 1094, 837 (Si–C), 658 cm

SiMe₂); 0 89 (s, 9H, Bu^tSi); 1 59 (s) and 1 62 (s, total 3H,

2-Me); 1 75–1 96 (m, 2H); 3 58–3 83 (m, 4H); 4 11–4 40 (m,

2H); 5 09–5 23 (t, J 6 1 Hz, 2H, Hm); 5 38–5 50 (t, J 6 0 Hz,

2954, 2857 4, 1970 and 1889 (CO),

1

max

.

0 05 (s, 6H,

H

1H, Hp); 5 74–5 78 (d, J 6 3 Hz, 2H, Ho).

2 3 (SiMe₂);

C

18 2 (SiCMe₃); 25 9 (SiMe₂); 28 2 (Me); 28 3 (Me); 29 7

(Me); 35 0 (CH₂); 36 4 (CH₂); 36 9 (CH₂); 59 8 (CH₂); 69 8

(CH₂); 70 5 (CH₂); 70 7 (CH₂); 73 7 (CH); 75 0 (CH); 75 3

(CH); 88 3 (CH); 88 4 (CH); 88 6 (CH); 88 8 (CH); 92 8

(CH); 92 9 (CH); 93 1 (CH); 94 9 (CH); 99 3 (C); 100 5 (C);

106 5 (C); 113 6 (C); 113 8 (C); 119 9 (C); 232 7 (Cr(CO)₃).

Tricarbonyl[(2 S,4 S)-2-methyl-2-( ⁶-phenyl)-1,3-dioxan-4-

methanol]chromium (48) and Isomers (49)–(53)

Tricarbonyl[(1,1-dimethoxyethyl)- ⁶-benzene]chromium (46)

(^A) The acetal mixture (33)–(38) (from thermodynamic con-

trol; 0 521 g, 2 50 mmol) and Cr(CO)₆(0 801 g, 3 64 mmol)

were re uxed in Bu₂O (18 0 ml) and tetrahydrofuran (2 0 ml)

under a ow of nitrogen until a green tinge appeared. Workup

and ash chromatography (hexanes/Et₂O, 3 : 7) gave a mixture

of the isomers (48)–(53) as a yellow oil (0 304 g, 35%) (Found:

M⁺, 344 0348. C₁₅H₁₆CrO₆requires M⁺, 344 0352). m/z

344 (17%, M⁺), 260 (53, M 3CO), 188 (47), 172 (37), 126

(1,1-Dimethoxyethyl)benzene (32) (0 996 g, 6 00 mmol) and

Cr(CO)₆(1 986 g, 9 03 mmol) were re uxed in Bu₂O (36 0 ml)

and tetrahydrofuran (4 0 ml) under a ow of N₂for 39 h.

Workup and ash chromatography (hexanes/Et₂O, 9 : 1) gave

the following compounds. (i) Tricarbonyl[(1-methoxyethenyl)-

⁶-benzene]chromium (47) was obtained as a yellow solid

(114 mg, 7%), m.p. 63–65 C.

1616 (C=C), 1313, 1258, 1124, 1038, 658, 629 cm

(s, OMe); 4 26 (s, one of =CH₂); 4 59 (s, one of =CH₂);

5 12–5 55 (m, Ph–H); 5 55–5 90 (m, Ph–H). 55 6 (OMe);

2938, 1963 and 1879 (CO),

(29), 105 (25, PhCO⁺), 52 (100, Cr⁺).

2948, 2887, 1963 and 1866 (CO), 1413, 1177, 1052, 660, 631,

3389 (OH),

max

1

.

3 71

H

1

538 cm

.

1 50–2 03 (m including 1 60, (s) and 1 63

H

C

(s), 5 0H); 3 62–3 93 (m including 3 64–3 72 (t, J 7 9 Hz),

1 8H); 4 14–4 31 (ddd, J 16 4, 7 9, 5 7 Hz, 1 2H); 4 32–4 55

(m, 0 1H); 5 09–5 19 (t, J 6 2 Hz, 2H, Hm); 5 41–5 52 (m,

83 1 (=CH₂); 89 8 (Co or Cm); 91 8 (Co or Cm); 94 2

(Cp); 98 9 (Cipso); 163 9 (C=); 232 7 (Cr(CO)₃). (ii) The

tricarbonylchromium complex (46) was obtained as a yellow

1H, Hp); 5 67–5 74 (d, J 6 1 Hz, 2H, Ho).

27 8; 29 7;

C

crystalline solid (0 96 g, 53%), m.p. 96–98 C (Found: M⁺

,

34 5; 35 4; 60 0; 70 2; 75 5; 75 8; 88 8; 93 0; 95 0; 95 4;

107 0; 232 7 (Cr(CO)₃).

302 0250.

(12%, M⁺), 271 (22, M OMe), 218 (27, M 3CO), 186 (49),

135 (44), 114 (55), 52 (100, Cr⁺).

3093, 2968, 1976

and 1887 (CO), 1456, 1038, 635, 537 cm

3 20 (2 OMe); 5 13–5 23 (t, J 6 5 Hz, Hm); 5 41–5 48 (t,

J 6 3 Hz, 1H, Hp); 5 75–5 80 (d, J 6 0 Hz, Ho). 25 9

C

₁₃H₁₄CrO₅requires M⁺, 302 0246). m/z 302

(^B) A solution (1 0 ml) of trimethylsilyl tri uoromethane-

sulfonate (0 05 ml, 0 26 mmol) in dry CH₂Cl₂(10 ml)

was cooled to 23 C. The dioxadisiladecane (15) (141 mg,

0 438 mmol) was added followed by a solution of tricarbonyl[1-

max

1

.

1 61 (Me);

H

(

⁶-phenyl)ethanone]chromium (45) (105 mg, 0 410 mmol) in

C

(Me); 49 0 (OMe); 89 1 (Co or Cm); 93 9 (Co or Cm); 94 6

(Cp); 99 5 (Ph–C); 111 7 (Cipso); 232 7 (Cr(CO)₃). (iii)

CH₂Cl₂(1 0 ml). The solution was stirred for 5 5 h before

Et₃N (3 drops) was added and the mixture warmed to room tem-

perature. Workup and ash chromatography (hexanes/Et₂O,

1 : 1) gave (i) the tricarbonylchromium complex (45) (74 mg,

70%) as an orange oil; and (ii) the isomers (48)–(53) (10 mg)

as a yellow oil.

The tricarbonylchromium complex (45) (15 mg, 1%).

max

1

1970 and 1900 (CO), 1687 cm

(C=O).

2 46 (COMe);

H

5 23–5 31 (t, J 6 5 Hz, Hm); 5 60–5 68 (t, J 6 3 Hz, Hp);

6 03–6 08 (d, J 6 0 Hz, Ho).

(^C) A solution (1 0 ml) of trimethylsilyl tri uoromethanesul-

fonate (0 05 ml, 0 26 mmol) in dry CH₂Cl₂(10 0 ml) was cooled

to 23 C. The dioxadisiladecane (15) (159 mg, 0 494 mmol)

then a solution of tricarbonyl[(1,1-dimethoxyethyl)- ⁶-benzene]-

chromium (46) (141 mg, 0 467 mmol) in CH₂Cl₂(1 0 ml) were

added. The solution was stirred for 8 h before Et₃N (4 drops)

was added and the reaction mixture warmed to room tempera-

ture. Workup and ash chromatography (hexanes/Et₂O, 1 : 1)

gave the following compounds. (i) The tricarbonylchromium

complex (45) (19 mg, 16%). (ii) The isomers (48)–(53) as a

References

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yellow oil (54 mg, 34%).

and 1875 (CO), 1413, 1176, 1052, 660 631, 536 cm

3392 (OH), 2950, 2887, 1963

1

max

4

.

H

1 58–1 74 (m including 1 61 (s) and 1 64 (s), 4 7H); 1 74–2 12

(m including 1 84–1 94 (q, J 5 9 Hz), 4 4H); 3 63–3 75 (t,

J 7 7 Hz, 1 3H); 3 84 (br s, 2 7H); 4 15–4 32 (ddd, J 16 0,

7 9, 5 8 Hz, 1 2H); 4 32–4 58 (m, 0 7H); 5 11–5 21 (t, J

6 3 Hz, 2 1H, Hm); 5 43–5 53 (m, 0 9H, Hp); 5 67–5 78 (dd,

5

6

7

J 6 8, 0 8 Hz, 2 0H, Ho).

28 0; 29 9; 34 5; 35 4; 60 2;

C

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232 7 (Cr(CO)₃).

8

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14

15

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21

22

23

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36

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25

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Article Doi

Towards the diastereoselective functionalization of non-racemic acetal derivatives of η6-arylcarbonyl complexes of tricarbonylchromium

DOI: 10.1071/C98054

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Article abstract of DOI:10.1071/C98054

Full text of DOI:10.1071/C98054

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