alicyclics (1)

7/25/2019 Alicyclics (1)

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Alicyclics

Aliphatic compounds containing rings,

cycloalkanes, cycloalkyl halides,cycloalkyl alcohols, cyclic ethers,

cycloalkenes, cycloalkadienes, etc.


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Cycloalkanes

H2C

H2C

CH2H2C

H2C CH2

CH2 H2C

H2C CH2

CH2

H2C H2C

H2C CH2

CH2

CH2

H2C

cyclopropane cyclobutane cyclopentane cyclohexane


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CH3

BrBr Br Br

CH3

H3C

methylcyclopentane 1,1-dimethylcyclobutane

trans-1,2-dibromocyclohexane

Br

Br


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HO

HO

HO OHHO OH

cis-1,2-cyclohexanediol


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cyclopentene 3-methylcyclohexene 1,3-cyclobutadiene

1

2

3

4

5

cycloalkenes


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OH

O

CH2CH3

cyclohexanol ethyl cyclopentyl ether

cyclohexyl alcohol


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Cycloalkanes, syntheses!

A. "odi#ication o# a ring compound!

1. reduction o# cycloalkene

2. reduction o# cyclic halide

a$ hydrolysis o# %rignard reagent

b$ acti&e metal ' acid

3. Corey (ouse

). *ing closures


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A. "odi#ication o# a cyclic compound!

Br

Br

(2, +i

n, (Cl

"g then (2


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Br Li2

CuLi

/i Cu0

C(3C(2-)r C(2C(3

must be 1o

Corey-(ouse


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). ring closures

C(2C(2 C(2C, h&

)r-C(2C(2C(2C(2C(2-)r n

etc.


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cycloalkanes, reactions!

1. halogenation

2. combustion

3. cracking

4. exceptions

ClCl2, heat

(Cl


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exceptions!

(2, +i, o

C(3C(2C(3

Cl2, 6eCl3Cl-C(2C(2C(2-Cl

(2, (

C(3C(2C(2-(

conc. (24

C(3C(2C(2-3(

(0C(3C(2C(2-0


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exceptions 7cont.$

(2, +i, 2o C(3C(2C(2C(3

8888888888


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internal bond de&iation heat o#

angles #rom 19.5 combustion

o

-49.5o

1.

9o -19.5o 14.

1o

-1.5o

15.:


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Cyclopropane undergoes addition reactions that othercycloalkanes and alkanes do not. ;his is because o#

angle strainin the small ring. )ecause the bond angles

are less than the optimal 19.5o#or maximum o&erlap,

the bonds are


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internal bond de&iation heat o#

angles #rom 19.5 combustion

o -49.5o 1.

9o -19.5o 14.

1o -1.5o 15.:

12o 11.5o 15:.4

12.5o 19o 15.3

135o 25.5o 15.


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Cyclohexane does not ha&e

any angle strain> 0t isn?t a #lat

molecule. )y rotating about

the carbon-carbon bonds, it can

achie&e 19.5obond angles.


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chair t


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;he chaircon#ormation o# cyclohexane is #ree o#

both angle strain and torsional strain 7de&iation

#rom staggered$. ;his is the moststable

con#ormation.


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;he boat con#ormation is #ree o# angle strain, but has a

great deal o# torsional strain 7eclipsed$. ;o relie&e the

strain, it t


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a a

a

a

a

a

e

ee

ee

e

a axial positions in the chair con#ormation

e e@uatorial positions


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CH3

H3C

C(3in axialposition C(3in e@uatorialposition

is more stable


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O

H

HO

H

HO

H

OHOHH

H

OH

O

H

HO

H

HO

H

HOHH

OH

OH

CHO

OHH

HHO

OHH

OHH

CH2OH

beta-D-glucose alpha-D-glucose

all groups equatorial one group orced to be axial

!ore stable


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Cycloalkenes, syntheses!

A. "odi#ication o# a ring compound!

1$ dehydrohalogenation o# an alkyl halide

2$ dehydration o# an alcohol

3$ dehalogenation o# &icinal dihalides

7). *ing closures$


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OH

Br

Br

Cl (7alc$

(, B

n

cyclohexene


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Cycloalkenes, reactions!

1. addition o# (2 . hydroboration-oxid.

2. addition o# 2 9. addition o# #ree radicals

3. addition o# ( 1. addition o# carbenes

4. addition o# (24 11. epoxidation

5. addition o# (2,( 12. hydroxylation

. addition o# 2 (2 13. allylic halogenation

:. oxymerc-demerc. 14. oDonolysis

15. &igorous oxidation


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Br

Br

trans-1,2-dibromocyclohexane

(2, Et

)r2, CCl4


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H2C

H2C

CH2

CH

C

H2C CH3

" HBr

H2C

H2CCH2

CH2

C

H2

C CH33ocarbocation

Br H2C

H2CCH2

CH2

C

H2C

Br

CH3


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Br

O#O3H

OH

()r

(24

(2, (

"arko&niko& orientation


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)r2

7a@.$


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OH

OH

H2O, Hg$O%c&2 'aBH(

$BH3&2 H2O2, 'aOH

)ar*o+ni*o+

anti )ar*o+ni*o+


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()r, peroxides

C(2C, hF

EeroxybenDoic acid


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OH

OH

OH

OH

Br

cis-1,2-cyclohexanediol

trans-1,2-cyclohexanediol

"n4

(C3(

)r2, heat


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OCHCH2CH2CH2CH2CHO

HO2CCH2CH2CH2CH2CO2H

O3 H2O,-n

.)nO(, heat


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Br2 .)nO( HCO3H

Br HO OH HOBr OH

anti syn anti

stereoselecti&e


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cyclic alcohols, halides, ethers as expected!

OH

OH

OH

HO

O'a

Br

O

H3CC

O

O

E)r3

+a

C(3C( (

+aCl


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+a(2oalkyl halide G H2

"g (2


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Alicyclic compounds are chemically

like their open chain analogs. ;he

exceptions are #or small ring

compounds


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Hpoxides!

CH2H2C

OCHH2C

O

CH3 O

O

ethylene oxide propylene oxide cyclopentene oxide

7oxirane$ 7methyloxirane$

C(5C3(

ynthesis!

I-butylene oxidecis-2-butene


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epoxides, reactions!

1$ acid catalyDed addition

CH2H2C

O

CH2H2C

O

CH2H2C

O

(2, (

C(3C(2(, (

()r

(

C(2C(2(

(C(3C(2--C(2C(2

(

C(2C(2)r


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CH2

H2C

O

CH2H2C

O

CH2H2C

O

CH2H2C

O

'aOH, H2O

'aOCH2CH3

CH3CH2OH

'H3

1/ CH3CH2)gBr

2/ H2O

(

C(2C(2(

C(3C(2--C(2C(2-(

(2+-C(2C(2-(

C(3C(2C(2C(2-(

2. )ase catalyDed addition


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CCO

" H CCOH

CC

OH

" 0H D# C C

H

OH

C C

H

OH

C C

OH

" H

1&

2&

3&

mechanism #or acid catalyDed addition to an epoxide


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mechanism #or base-catalyDed addition to an epoxide!

CC

O

C C

OH

1&

2&

" C C

O

D#

C C

O

" H "


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acid catalyDed addition to unsymmetric epoxides8

CH2CHO

H3C

CH2CH

O

H3C

( (2, (

C(3C(C(2 (


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CH2CHO

H3C

CH2CHO

H3C

C(3

C(3(,( C(3C(C(2

(

)r

()r C(3C(C(2 (


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CH2CHO

H3C

CH2CHO

H3C

CH2CHO

H3C

)ase8

1( +a1(, (2

1 C(3C(C(2 (

+(2 +(3 C(3C(C(2 (

C(3 C(

3(, C(

3+a C(3C(C(2

(


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CH2CHO

H3C

CH2CHO

H3C

Acid!

)ase!

( C(3C(C(2 (

-, ( C(3C(C(2 (


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J&ariable transition stateK

acid! L C L C L

(

M

M

N

base!

L C L C L

M-

N

)ond breaking is

occurring #aster thanbond making, making the

carbon slightly positi&e.

C M! 3oG 2oG 1o

)ond breaking is occurring

at the same time as bond

making, there is no chargeon the carbon. teric

#actors are most important!

1oG 2oG 3o


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CH2CHO

H3C

CH2CHO

H3C

Acid!

)ase!

( C(3C(C(2 (

-, ( C(3C(C(2 (

CM! to 2ocarbon

steric #actors! to 1ocarbon

alicyclics (1)

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