2ND YEAR ORGANIC PROBLEM CLASSES 2003/2004
Class to be held at 3pm on Monday 19th January 2004 in normal tutors groups
Answers to be handed in to Prof Rzepa's office Rm 169 (C2) before 3 pm on the day of the class. Late scripts will receive no credit.
Please write your own name AND YOUR TUTORS NAME on your script.
Question 1.The following sequence is part of a biomimetic synthesis of propionate derived natural products. The tetraene ester is heated to give the tricyclic core B of the natural system, via a presumed intermediate A. Propose a structure for A (10 marks), mechanisms leading to it and B, including nomenclature (10 marks) and using your knowledge of the predicted stereochemistry of your mechanistic steps, predict what the stereochemistry is of the centre to which the ester group E is attached (5 marks).
Question 2.The biomimetic synthesis of a potent microtubule-stabilizing agent involves the use of an acyclic precursor C to create the complex pentacyclic chemotherapeutic molecule F, forming seven new stereogenic centres in a fully diastereocontrolled fashion. The step C to D is a conventional macrocyclisation, whilst E to F is a simple lactonisation. Your task is the following;