Titanium promotes the pinacol coupling and then deoxygenates the products: the McMurry reaction

Titanium can be used as the metal source of electrons in the pinacol reaction and, provided the reaction is kept cold and not left for too long, diols can be isolated from the reaction, as in the example above. However, unlike magnesium or aluminium, titanium reacts further with these diol products to give alkenes in a reaction known as the McMurry reaction, after its inventor.

Notice that the titanium (0), which is the source of electrons in the reaction, is produced during the reaction by reacting a Ti (III) salt, usually TiCl₃, with a reducing agent such as LiAlH₄ or Zn/Cu. The reaction does not work with, say, powdered titanium metal. The McMurry reaction is believed to be a two-stage process involving firstly a pinacol radical coupling.

The Ti(0) then proceeds to deoxygenate the diol by a mechanism not fully understood, but thought to involve binding of the diol to the surface of the Ti(0) particles produced in the reduction of TiCl₃.

We expect you to be mildly horrified by the inadequacy of the mechanism above. But unfortunately, we can’t do much better because no-one really knows quite what is happening. The McMurry reaction is very useful for making tetrasubstituted double bonds—there are few other really effective ways of doing this. However, the double bonds really need to be symmetrical (in other words, have the same substituents at each end) because McMurry reactions between two different ketones are rarely successful.

McMurry reactions also work very well intramolecularly, and turn out to be quite a good way of making cyclic alkenes, especially when the ring involved is medium or large (over about eight members). For example, the natural product flexibilene, with a 15-membered ring, can be made by cyclizing a 15-keto-aldehyde.

اخر الاخبار

اخبار العتبة العباسية المقدسة

بيان لمكتب المرجعية العليا حول نشر صور السيد السيستاني في الأماكن العامة

متحف الكفيل: إنجاز المرحلة الرابعة من مشروع متحف العتبة العسكرية المقدسة

تضمن عرضًا مسرحيًّا.. شعبةُ الخطابة النسويّة تقيم مجلس عزاء بذكرى شهادة الإمام الحسن (عليه السّلام)

الأمين العام للعتبة العبّاسية المقدّسة يتفقد مجموعة مواكب أمّ البنين (عليها السلام) لخدمة الزائرين

المزيد

الآخبار الصحية

تسارع الشيخوخة.. متى يبدأ وأي الأعضاء أكثر تأثرا؟

9 مسببات شائعة للالتهاب المزمن قد تهدد صحتك

باحثون يطورون علاجا لهشاشة العظام.. النتائج مذهلة

تحمي من أمراض عديدة.. 6 فوائد لتناول البطاطا الحلوة

المزيد

الآخبار التكنلوجية

عودة التعاون الفضائي بين روسيا وأميركا.. وبحث ملفات "هامة"

المعلمون في خطر.. خاصية جديدة في "تشات جي بي تي" تشرح الدروس

بشرى لمرضى الشلل.. شريحة في الدماغ قد تتيح التحكم بالأدوات

مدينة غارقة.. هل يخفي قاع البحر الكاريبي سرّ حضارة مفقودة؟

المزيد

مواضيع ذات صلة

The Hammett relationship

Systematic structural variation

Crossover experiments

Labelling experiments reveal the fate of individual atoms

Be sure of the structure of the product

Variation in the structure of the aldehyde

formation of an ester intermediate

formation of an intermediate dimeric adduct

Be sure of the structure of the product

Variation in the structure of the aldehyde

Proposed mechanism C: formation of an ester intermediate

Proposed mechanism B: formation of an intermediate dimeric adduct