Sharpless asymmetric epoxidation template

The tartrate replaces two isopropoxides on titanium; the allylic alcohol and tert-butyl hydroperoxide then bind as alkoxides. The peroxide oxygen is delivered to one face of the C=C, fixed by the chiral tartrate, and exchange with fresh substrate releases the epoxy alcohol. L-(+)-DET turns (E)-hex-2-en-1-ol into the (2S,3S)-epoxide.

Mechanism step by step

Ti(OiPr)₄, diethyl tartrate and TBHP epoxidise allylic alcohols with high ee

1. Chiral catalyst – L-(+)-DET replaces two OiPr groups (drawn as a monomer; the real catalyst is a dimer)
2. Loading – The allylic alcohol and TBHP replace the last two OiPr groups
3. Oxygen transfer – The C=C takes the Ti-bound peroxide O from one face; the O–O bond breaks (peroxide drawn η¹)
4. Turnover – Fresh allylic alcohol and TBHP displace the epoxy alcohol and t-BuOH

Key points

• Only allylic alcohols react: the OH binds to Ti and holds the C=C next to the peroxide; other C=C bonds (as in geraniol) are left alone.
• Mnemonic: draw the C=C upright with CH₂OH at the lower right; L-(+)-DET delivers O from the bottom face, D-(−)-DET from the top.
• Catalytic Ti (5–10 mol%) with 4 Å molecular sieves; ee usually > 90%. Secondary allylic alcohols undergo kinetic resolution.
• Sharpless shared the 2001 Nobel Prize in Chemistry for asymmetric oxidations.

Drawn with 271 atoms, 8 arrows, 6 shapes – every one editable in MolDraw.

Sources

• Kürti & Czakó, Strategic Applications of Named Reactions in Organic Synthesis, Elsevier 2005, Sharpless asymmetric epoxidation Textbook
• Clayden, Greeves & Warren, Organic Chemistry, 2nd ed., OUP 2012, ch. 41 Textbook
• Smith, March's Advanced Organic Chemistry, 8th ed., Wiley 2020, ch. 15 Textbook