Oxidation of aldehyde to acid or ester

1. Jones reagent
acidic condition, strong oxidant.

2. I2/MeOH/KOH
forms methylester. mild condition, alkene is untouched.
can't make t-buylester by this way.
tert-aldehyde is more reactive than sec-aldehyde.

3. KMnO4/PH buffer/t-BuOH/water
mild condition, benzyl ether untouched.

4. NaClO2, t-BuOH, PH buffer
mild condition, works for very hindered aldehydes.
t-amlyne used to prevent alkenes from oxidation.

aldehyde to terminal alkyne

1. OhiraReagent and derivatives
diazoketophosphonium ester.

2. Corey-Fuchs Reaction
tetrabromomethane/pph3, then base.
or
trichloroacetic acid /base

one carbon elongation

1. aldehyde to aldehyde
step 1. aldehyde + PPh3Cl-CH2OMe/t-BuOK
step 2. Formic acid.

Wiki is a good source of infomation:

Examples of homologation reactions include:

• Seyferth-Gilbert homologation
• Displacement of a halide by a cyanide group, which can be reduced to an amine, see: Kolbe nitrile synthesis
• Kiliani-Fischer synthesis, where an aldose molecule is elongated through a three-step process consisting of:
  1. Nucleophillic addition of cyanide to the carbonyl to form a cyanohydrin
  2. Hydrolysis to form a lactone
  3. Reduction to form the homologous aldose
• Wittig reaction of an aldehyde with methoxymethylenetriphenylphosphine, which produces a homologous aldehyde.
• Arndt-Eistert synthesis is a series of chemical reactions designed to convert a carboxylic acid to a higher carboxylic acid homologue (ie. contains one additional carbon atom)
• Kowalski ester homologation, an alternative to the Arndt-Eistert synthesis. Has been used to convert β-amino esters from α-amino esters through an ynolate intermediate.^[2]

Some reactions increase the chain length by more than one unit. For example, the following are considered two-carbon homologation reactions:

• Nucleophilic addition to ethylene oxide, resulting in a ring-opening and producing a primary alcohol with two extra carbons.
• Malonic ester synthesis, which produces a carboxylic acid with two extra carbons.