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Organic > Grainger - Functional group transformation > Flashcards

Grainger - Functional group transformation Flashcards

1
Q

What are the key features of the matterson rearrangement?

A

Boronic rearrangement

Stereospecific migration of Me from reagent

Halo Boronic dimer + RMgBr -> R Boronic Dimer + halo MgBr

R = alkyl group

Inversion of configuration

Sn2-like o

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2
Q

Explain the structure of boron

A

sp2 hybridisation 1s2 (2s2)3 2Pz0

3 valence electrons and can therefore form 3 covalent bonds (after hybridisation)

total of 6 electrons

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3
Q

How does boron achieve an octet?

A

Dimerisation - each atom within the dimer is still electron deficient

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4
Q

Boron is a _______ acid because boron is an _______________________________

A

A Lewis acid

Electron pair acceptor

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5
Q

What factors affect Lewis acidity of Boron?

A

1) degree of positive charge on the boron
2) degree of pi-pi bonding
3) effect of pi-pi bonding based on orbital sizes and orbital energy

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6
Q

Electronegativity of Boron

A

2.01

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7
Q

Electronegativity of carbon

A

2.55

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8
Q

Electronegativity of hydrogen

A

2.2

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9
Q

Based on Boron’s electronegativity - how is the atom’s nature described?

A

Metallic

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10
Q

What is an olefin?

A

Double bond - ALKENE

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11
Q

How do you make an alcohol from borane and an olefin?

A

i) BH3•THF

ii) NaOH and H2O2

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12
Q

What are i) inductive effects ii) mesomeric effects?

Which ones win?

A

i) polarisation of the sigma bond due to the electron withdrawing or donating effects
ii) polarisation due to pi bonding - conjugation

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13
Q

Electronegativity of silicon

A

1.90

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14
Q

Structure of silicon

A

4 valence electrons and can form 4 bonds after hybridisation

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15
Q

What happens to the stereochemistry of an SN2 reaction?

A

Inversion of configuration

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16
Q

What is the best description of substitution at a silicon centre? What are the key features?

A

Addition-elimination reaction

Backside attack at the tertiary silicone centre

Passed through an intermediate

Inversion of symmetry

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17
Q

Explain the beta-effect

A

A trigonal planar carbocations where the p atomic orbital is orthogonal to the 3 sigma bonds

Silicon

Hyper-conjugative stabilisation

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18
Q

How are alpha-carbon metal bonds stabilised

A

1) low energy empty 3AO’s allowing d pi - sp3 pi bonding
2) overlap between filled sigma orbital of metal to carbon and unfixed sigma star of carbon to silicon
3) Si is large therefore is relatively polarised therefore induced dipoles also help stabilise proximal negative charge

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19
Q

Explain the use of silyl ethers

A

Good protecting group for -OH which is good with stability.

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20
Q

What is the driving force for a brook rearrangement?

A

Si-O Bond strength&raquo_space;» Si-C bond strength

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21
Q

Explain the steps of a brook rearrangement

A

ROHSiMe3 mixed with Et2NH

Equilibrium reaction throughout

Passing through a 5 coordinate intermediate (3 membered ring)

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22
Q

Define regiosectivity

A

Preference of making one direction of chemical bond making/breaking over all other possible directions

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23
Q

Define chemoselectivity wrt olefination

A

The type of carbonyl groups that are reactive relative to one another

24
Q

Define stereoselectivity wrt olefins

A

Can exist as E or Z - olefination in a predictable fashion

25
Q

What does “base induced” olefination form?

A

Z ALKENE

26
Q

What’s the best bases for base induced olefination?

A

KF/THF and room temp

27
Q

What is an alternative name for the base induced olefination reaction?

A

Peterson reaction

28
Q

What is the product of the acid-mediated olefination?

A

an E ALKENE

29
Q

mCPBA structure

A

Benzene ring
Position 2 COOOH
Chlorine on position 4

30
Q

Reaction conditions for a stereospecific epoxidatoion of a silyl ALKENE?

A

mCPBA CH2CL2 (65%)

31
Q

What reaction pathway would be taken to obtain a diastereoisomerically pure Z-alkene product? Silyl chemistry

A

Step 1) Z alkene to be reacted with mCPB, CH2Cl2 affording an epoxide which has the initial stereochemistry of the alkene
Step 2) RPr2CuLi to afford an alkane where stereochemistry is still retained
Step 3) React with Et2O.BF3

32
Q

What reaction pathway would be taken to obtain a diastereoisomerically pure E-alkene product? Silyl chemistry

A

Step 1) Z alkene to be reacted with mCPB, CH2Cl2 affording an epoxide which has the initial stereochemistry of the alkene
Step 2) RPr2CuLi to afford an alkane where stereochemistry is still retained
Step 3) React with KH

33
Q

When labelling the Newmann Projection of the Felki-Ahn model - which group goes perpendicular to the plane of the carbonyl?

A

The LARGE group

34
Q

What is the Wittig reaction?

A

Aldehyde/Ketone + Phosphonium Ylide –> Alkene + O=P(R5)3

35
Q

How do you form a Phosphinium Ylide reagent?

A

Phosphonium salt plus appropriate base

36
Q

How is a phosphonium salt formed? What reaction pathway is this?

A

alkyl halide + phosphine (Ph3P)

SN2-substitution

37
Q

When forming a phosphonium salt which reaction conditions are needed for an activated RX? Where the compound is primary, benzylic and X=Br or I?

A

CHCl3 OR THF at 50 degrees C

38
Q

When forming a phosphonium salt which reaction conditions are needed for branched alkyl halides and if X=Cl?

A

elevated temperatures EG toluene (111 degrees C) or xylene (140 degrees C).

39
Q

What are the three classifications of a phosphorus Ylide and what do they form?

A

1) ‘Non-stabilising’ ylides provide Z-olefins
2) Semi-Stabilising Ylides provide a mixture of E and Z
3) Stabilised Ylides provide E-olefins

40
Q

What makes a non-stabilising ylide?

A

R = alkyl group

41
Q

What makes a Semi-stabilised ylide?

A

Aromatic or conjugated ylide system

42
Q

What makes a stabilised ylide?

A

Electron withdrawing group (Such as O or S being present) (AKA Anion stabilising group_

43
Q

Under Salt free non-stabilising ylide conditions - why does the Z isomer form when it’s the most energetically unflavoured?

A

KINETICS

Formation of the Z ring system has a much faster rate than the E ring system leading the Z isomer to dominate

44
Q

What are the optimum conditions for forming a highly Z-selective yield with non-stabilised ylides?

A

1) salt free conditions (Ie use Na or K bases to prepare the ylide)
2) Use Ph3P=CHR
3) non-protic, polar solvents such as THF
4) Avoid statically encumbered substituents on the aldehyde and ylide
5) maintain a low temperature (<75 degrees C)

45
Q

Explain there Horner-Wadsworth-Emmons Reaction

A

Phosphonate reacting with NaH and THF to form a phosphonate carbonate.

React with aldehyde/ketons to form alkene plus water soluble phosphonate

46
Q

How are phosphonates formed? explain the reaction

A

Arbusov Reaction

Driving force is the new P=O bond
Needs an alpha anion stabilising substituent
Solvents include PhH, toluene, THF and DMSO
Bases include NaH or KH

47
Q

What is an allyl?

A

a terminal alkene

48
Q

What is an allyl alcohol?

A

HO-CH2-CH=CH2

49
Q

What is the allylation general reaction?

A

Aldehyde + allyl metal -> homoallylic alcohol

50
Q

What are the types of Allyl Metal Reagents?

A

Type 1 - allyl boranes, allyl boronates - HIGHLY STEREOSELECTIVE via a closed/cyclic transition state

Type 2 - Allyl metals (M=Si, Sn) with aldehydes and BF3 catalysis (Si Id less electropositive than Sn) and tends to require more forcing via an open or acyclic transition state

51
Q

What does ‘anti’ mean?

A

The groups are on opposed sides (basically E)

52
Q

What does ‘syn’ mean?

A

The groups are on the same side (basically Z)

53
Q

How are the reaction conditions altered to afford an anti or a syn product in allylation?

A

Start with the corresponding allyl metal

54
Q

How does the energy compare for the transition state of a syn and an anti allylation?

A

Energy are the same

55
Q

Explain the regio, stereospecific and stereoselective natures of the type 1 allegations

A

Regio - B add to less substituted end of the double bond
Stereoselective - Adds to the less statically hindered bottom face of alkene
Stereospecific - B and H add syn

56
Q

Lewis acid for type 2 allyl metals

A

BF3.OEt2

57
Q

Which mechanism is best to describe the basic reaction of a type 2 allyl metal?

A

SN2’

Organic (2 decks)

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