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Synthetic Methodology > Westwood > Flashcards

Westwood Flashcards

1
Q

in a double bond, which side does a boron prefer to add to?

A

least substituted

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2
Q

name some alternative boron agents

A

thexylborane, 9-BBN, disiamylborane, dicuclohexylborane, catechol borane, pineocamphylborane

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3
Q

what is the benefit of catechol borane? How?

A

doesn’t reduce an alkyne to an alkane - stops at alkene due to O lone pairs donating into empty p orbital on B

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4
Q

what is a good activating solvent in an organoboron experiment?

A

THF

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5
Q

How would you go R-B to R-X-B?

A

R migration

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6
Q

in an R migration, how would the migrating and leaving group be orientated?

A

antiperiplanar

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7
Q

what nucleophile is used to go from R-B to B-OH?

A

peroxide (O-OH)-

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8
Q

what reagents used in a protonolysis?

A

diglyme

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9
Q

what charge does boron need to have to do a migration?

A

negative

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10
Q

how would you get evidence of mechanisms of reduction of alkynes/alkenes?

A

D/H

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11
Q

for alkenylborane reactions, does a halogenation or amination retain or inverse the configuration?

A 
halogenation = inversion
amination = retention
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12
Q

how would a NCl3 react with an alkenylborane

A

via radicals

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13
Q

in a carbonylation of alkenylboranes, what reagent gives an aldehyde?

A

i) LiAlH(OMe)3

ii) H2O2 in NaOH

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14
Q

in a carbonylation of alkenylboranes, what reagent gives a ketone?

A

i) H2O

ii) H2O2 in NaOH

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15
Q

in a carbonylation of alkenylboranes, what reagent gives a tertiary alcohol?

A

i) ethylene glycol

ii) H2O2 in NaOH

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16
Q

in the cyanidation of alkylboranes, what type of compound do you get if you use 2 equiv OTf2?

A

tertiary alcohol

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17
Q

in the cyanidation of alkylboranes, what type of compound do you get if you use 1 equip OTf2 followed by H2O2 in base?

A

ketone

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18
Q

what would you use to aminate an alkenylborane?

A

Cl-NH2 or HSO3O-NH2 (NH2 with good leaving group)

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19
Q

what products would you get if you react BR3 with an a-halocarbonyl? And what intermediate?

A

3 x a-R-carbonyl

intermediate = enolate

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20
Q

If you have an alkyne (R—H), what reagents would you use to get a cis alkene product?

A

i) R2BH

ii) I2 in NaOH

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21
Q

If you have an alkyne (R—X), what reagents would you use to get a trans alkene product?

A

i) R2BH
ii) NaOMe
iii) AcOH

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22
Q

If you have an alkyne (R—H), what reagents would you use to substitute another R group?

A

i) nBuLi
ii) R3B
iii) I2

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23
Q

what happens when you react disiamylborane with alkynes?

A

can combine 2 alkynes to forma dialkyne product (with the help of I2)

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24
Q

how do you make a trans dialkene from a dialkyne

A

i) 2x sia2BH

ii) RCO2H

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25
Q

how would you retroborate? Do you get the same alkene out that you put in?

A

apply heat to remove a proton - alkene generated depends on which proton is removed in the retroboration.

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26
Q

Which is unstable to rearrangement of allylboranes: B(OR)2 or BR2 (AKA which undergoes the rearrangement?)

A

BR2

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27
Q

what structure does an allylborane reaction with carbonyls look like?

A

a chair conformation of a cyclohexane

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28
Q

what is a thiirane?

A

an epoxide (ring) with an S in it

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29
Q

what is a sulfide?

A

an ether with an S instead

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30
Q

which bond is stronger OH or SH?

A

OH (orbital overlap)

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31
Q

What type of addition does PhCH2SH do?

A

1,4 (as it is very nucleophilic)

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32
Q

what reagents could you use to synthesise thiols?

A

Ph—X with S=C(NH2)2 + NaHCO3 // Na2S2O3 + H3O+ // KSCsOEt + LiAlH4 //Na2S2 (non Ph R group) + Na/liqNH3 + H3O+

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33
Q

how would you synthesise aromatic thiols?

A

ClSO3H (chlorosulfonylation) + Zn, H3O+ // S8 with PhLi

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34
Q

what bonds are changing in the oxidation of thiols?

A

2xSH to SS

35
Q

what reagents are used to break up a thioacetal ring?

A

Hg2+, HgCl2 in H2O

36
Q

How would you substitute H for R on a thioacetal?

A

i) nBuLi + ii) RX

37
Q

2 methods of sulphide synthesis?

A

di-Cl alkane treated with Na2S to substitute 1xCl then nucleophilic attack to remove the Cl.
Attack of nucleophilic carbon atom at electrophilic sulfur

38
Q

What is an ylide?

A

a molecule with a permanent positive and negative charge.

39
Q

is a stabilised ylide hard or soft?

A

hard

40
Q

does sulfonium prefer axial or equatorial attack at a C=O on a cyclohexane ring?

A

axial

41
Q

When attacking a C=O-C=C, depending on if the ylide is soft or hard, an epoxide and a cyclopropane are formed. Which forms which?

A

unstabilised, soft, forms epoxide

stabilised, hard, forms cyclopropane

42
Q

what type of elimination does a sulfoxide do?

A

syn

43
Q

what reagents do you need to use for an elimination by a sulfoxide?

A

i) LDA
ii) (PhS)2
iii) NaIO4 + Heat

44
Q

what can dimsyl sodium do?

A

a) form a 1-alkene on long chain alkane
b) substitute with OH in COOH to form a ketone
c) add to a ketone to form an alcohol

45
Q

what are the three sulfur compounds that are oxidised and reduced to each other - similar to alcohol to aldehyde to carboxylic acid?

A

sulfure –> sulfoxide –> sulfone

—> oxidation

46
Q

how does the stern oxidation work?

A

DMSO+(COCl)2 makes Cl-S-Me2 which is attacked by a terminal alcohol —-> oxidised to an aldehyde

47
Q

what are the different fates of alkoxysulfonium salts?

A

elimination, substitution at S, substitution at C, Pumerer reaction

48
Q

what does the Pummerer reaction do?

A

acylation of sulfoxide –> elimination to sulfonium ion –> acetation of sulfonium ion –> a-acyloxy-thioether

49
Q

What are some ways of synthesising sulphones?

A

oxidation of sulfides and sulfoxides // alkylation of sulfinate salts // rearrangement of sulfinate esters // friedel-crafts alkylation of sulfonyl halides // addition of sulfonyl halides to alkene or alkynes // cycloaddition reactions of SO2

50
Q

What is Bredt’s rule?

A

states that: a double bond cannot be placed at the bridgehead of a bridged ring system

51
Q

What is the Ramberg-backlund reaction

A

effectively removes an SO2 from the middle of a chain to form an alkene. with KOHH, tBuOH in CCl4, H2O

52
Q

Which isomer is produced during the Julia reaction? and what is it?

A

E (trans)

reductive elimination

53
Q

What are some methods for losing sulfone group?

A

Ramberg-Backlund // sulfinic acid elimination // reductive desulfonation // reductive elimination

54
Q

what reagents are used in the Eschenmosser fragmentation?

A

i) H2O2 in NaOH

ii) TsNHNH2

55
Q

What does Tschugaev elimination do?

A

removes two trans alcohols on an 8-membered ring to twist the ring and form a double bond (using P(OR)3 and a sulfur thing

basic: removes an OH to form an alkene using O-C=S bonds.

56
Q

What is the shapiro reaction?

A

removes a ketone to replace with a double bond next to it. [arylsulfonylhydrazones]

57
Q

how would you synthesise a sulfonamide/sulfonate ester?

A

Sn2 substitution with a Cl for an NH2R/ROH

58
Q

In which of Si-O vs C-O, Si-F vs C-F and Si-H vs C-H does the silicon version have a weaker bond?

A

Si-H

59
Q

How does silicon stabilise the B-cation?

A

donates e density into empty p orbital on the cation

60
Q

How does Si stabilise an a-C-M bond?

A

overlap of the bond with a d orbital on silicon

61
Q

What is a Brook rearrangement?

A

inserts O from C-OH to C-O-Si

62
Q

How do you synthesise a silyl enol ether?

A

trapping of enolate ethers // conjugate addition/silylation // hydrosilation

63
Q

what is an exceptional use of silyl enol ether?

A

formation of a quarternary center on a cyclohexane

64
Q

What reagent is useful for reactions of silyl enol ether with strong electrophiles

A

TiCl4

65
Q

what is siloxybuta-1,3-diene used in?

A

diels alder

66
Q

How do you synthesise B-hydroxysilanes?

A

reaction of a-metallated silanes with carbonyl compounds (Li or Mg good)
or ring-open with epoxysilanes

67
Q

what Si compound can act as a ‘masked’ carbonyl group?

A

vinyl silanes (Me3Si-=-R)

68
Q

Where does a compound substitute if its ipso?

A

on the same carbon in an aromatic ring

69
Q

What is hydrosilylation?

A

reduction of alkyne into an alkene using a Si compound

70
Q

What compound can be used to stop hydrosilylation reduction from going too far?

A

Pd-CaO3-PbO

71
Q

What intermediate does an electrophilic substitution reaction of a vinyl silane go through?

A

a stabilised B-carbocation

72
Q

In the Peterson Olefination (step 2) what reagent is used to produce an E alkene product?

A

NaH (causes a twist to coordinate the O to the Si which leaves)

73
Q

In the Peterson Olefination (step 2) what reagent is used to produce a Z alkene product?

A

AcOH (Si kicks off the app OH group)

74
Q

What reagent could be used to turn an OH into an X

A

Ph3P, CCl4 // POCl3, DMF

75
Q

What reagents would be used to form RCO2R (using a P reagent)

A

i) X2 + P(OEt)3 + pyridine
ii) RCO2H
iii) ROH

76
Q

reagents in the Mitsonobu reaction

A

DEAD and PH3P (takes PCO2H + alcohol –> ester)

77
Q

What ionic nitrogen intermediate compound can POCl3 make?

A

imine

78
Q

What phosphorus reagent splits up an ozonide ring?

A

PR3

79
Q

Julia Peterson reaction: what are the reagents used and what isomer is generated?

A

PPh3 is the nucleophile needs a base, an ylide is formed and reacted with a C=O, oxygen and phosphorus form an oxasphosphetane ring, either E/Z isomers are generated.

80
Q

In the Wittig reaction, using a stabilised ylide, which isomer is formed?

A

E only

81
Q

In the Wittig reaction, using an ustabilised ylide, which isomer is formed?

A

Z only

82
Q

What does the Wittig Reaction do?

A

complexes an ylide with a C=O to produce an alkene

83
Q

What does the HWE reaction do? Which isomer, why?

A

forms an E alkene from CHO - E alkene is faster for thermodynamic reasons

84
Q

What is the arbusov reaction?

A

Goes from (RO)3P + R-Cl to (RO)2RP=O

Synthetic Methodology (2 decks)

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