In the synthesis of daminozide an anhydride is used out of necessity rather than out of choice, but it often turns out that there are several alternative reagents all corresponding to the same disconnection. Paracetamol, for example, is an amide that can be disconnected either to amine + acyl chloride or to amine + anhydride.

Which reagent is best can often only be determined by experimentation—commercially, paracetamol is made from para-aminophenol and acetic anhydride largely because the by product, acetic acid, is easier to handle than HCl. In a retrosynthetic analysis, we don’t really want to be bothered by this sort of decision, which is best made later, so it’s useful to have a single way of representing the key attributes of alternative reagents. We can depict both anhydride and acyl chloride in this scheme as an ‘idealized reagent’—an electrophilic acetyl group MeCO+. We call such idealized reagents synthons. Synthons are fragments of molecules with an associated polarity (represented by a ‘ + ‘ or ‘–’) which stand for the reagents we are going to use in the forward synthesis. They are not themselves reagents, although they may occasion ally turn out to be intermediates along the reaction pathway. By disconnecting bonds to synthons rather than to actual reagents we can indicate the polarity of the bond-forming reaction we are going to use without having to specify details of the reagents.

We can apply these ideas to the synthesis of the herbicide 2,4-D (2,4-dichlorophenoxyacetic acid). The most reasonable disconnection of an ether is the C–O bond because we know that ethers can be made from alkyl halides by substitution with an alkoxide anion. We don’t at this stage need to decide exactly which alkyl halide or alkoxide to use, so we just write the synthons. Once the retrosynthetic analysis is done, we can go back and use our knowledge of chemistry to think of reagents corresponding to these synthons. Here, for example, we should certainly choose the anion of the phenol as the nucleophile and some functionalized acetic acid molecule with a leaving group in the α position.

We can then write out a suggested synthesis in full from start to finish. It isn’t reasonable to try to predict exact conditions for a reaction: to do that you would need to conduct a thorough search of the chemical literature and do some experiments. However, all of the syntheses in this chapter are real examples and we shall often give full details of conditions to help you become familiar with them.

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم العلاقات العامة يختتم فعاليات محطات فتية الكفيل الثقافية في محافظة نينوى

ما الخدمات التي قدّمها موكب أشبال الطفّ لزائري عاشوراء؟

العتبة العباسية المقدسة تنظّم مسيرات عزائية لإحياء ذكرى عاشوراء في نينوى

قسم الشؤون الفكرية يحيي ذكرى استشهاد الإمام الحسين (عليه السلام) في القارة الإفريقية

المزيد

الآخبار الصحية

تناول الجبن.. مفيد للجسم أم خطر يهدد صحتك؟

طبيبة أسنان تحذر.. لا تتجاهل هذه العلامة بعد التنظيف

يجب أن تأكل المزيد من الشمام هذا الصيف.. إليك السبب ؟

تأثير صحي كبير.. كم بيضة يجب أن تتناول يوميا؟

المزيد

الآخبار التكنلوجية

أداء خلايا البيروفسكايت الشمسية تحت الماء قد يزيد كفاءة تحويل الكهرباء

مسافة الأمان: أساس القيادة الآمنة وتجنب الحوادث

هل القيادة السريعة تعني استهلاك اكثر للوقود؟

لماذا يعتبر كوكب المريخ غير صالح للحياة؟

المزيد

مواضيع ذات صلة

E-selective reduction of alkynes using sodium in liquid ammonia

Amine synthesis using functional group interconversions

Functional group interconversion

Multiple step syntheses: avoid chemoselectivity problems

The E-selective Wittig reaction

The Z-selective Wittig reaction

Stereoselectivity in the Wittig reaction depends on the ylid

The Peterson reaction is stereospecific

The one-step Julia olefination

The Julia olefi nation is stereoselective

The Julia olefination is regiospecific and connective

Sulfoxide elimination—oxidation to enones