The combination of pot, atom and step economy (PASE) in the synthesis of organic molecules of medium complexity can lead to a significant 'greening' of a synthetic route. This is demonstrated by the synthesis of highly substituted tetrahydropyran-4-ones and is quantified by a series of recognised metrics, which demonstrate the efficiency of combining PASE over conventional synthetic strategies

This microreview surveys the literature over the last five years with regard to construction of functionalised tetrahydropyran (THP) rings in the context of the synthesis of natural products. The overview given is intended to provide a working knowledge of the area for those who are unfamiliar, and to refresh and remind those who do work in the area of the exciting developments in the field. While the construction of the THP rings in a number of natural products has been reviewed, we have attempted to highlight the different strategies by focusing on two natural products, namely phorboxazole and centrolobine as case studies. Over the last five years, these natural products have become a test bed for new methods for the construction of THP rings. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The synthesis of the C1-C19 bis-pyran unit of phorboxazole B has been achieved. The key pyran rings were constructed by means of an asymmetric Maitland-Japp reaction and a second Maitland-Japp resolution/cyclization reaction. The longest linear sequence was 14 steps, and the C1-C19 bis-pyran unit was formed in an impressive 10.4% yield.