The Mask

Taken from Ref (1).

This is a brilliant achievement from Prof. Miyaura’s group. (1) The work represents his masterstroke – the use of Rhodium-catalyzed asymmetric conjugate additions in organic synthesis. While the group has always been using boronic acids as the substrates for their system (2), they also advocate for the use of lithium triolborate version for the substrates (3). The impressive enantiomeric excess (ee) serves as a testament to the sophistication of this methodology.
The real reason to share this article is because it also illustrates of good example of using heterocyclic systems in organic synthesis. The furan system is indeed a ‘disguise’ for the carboxylic acid – all we need to unmask it – is to treat furan with ozone. Thus what the group is really driving at is to install the carboxylic acid functionality in a conjugative manner, but then they achieve that via the intermediate furan. Given the readily availability of heterocyclic systems and a well-documented literature, this type of strategy is worthy of note. Indeed, this topic has been reviewed extensively (4,5) and Prof. Myers’ book on the topic is highly inspiring (6). Another great testament to the creativeness of organic chemists.

Reference:
(1) Rhodium-Catalyzed 1,4-Addition of Lithium 2-Furyltriolborates to Unsaturated Ketones and Esters for Enantioselective Synthesis of -Oxo-Carboxylic Acids By Oxidation of the Furyl Ring with Ozone
Xiao-Qiang Yu, Tomohiko Shirai, Yasunori Yamamoto and Norio Miyaura
Chemistry An Asian Journal - Article first published online: 4 JAN 2011
DOI: 10.1002/asia.201000589

(2) For recent works, see: (a) Journal of Organometallic Chemistry, Volume 692, Issues 1-3, 1 January 2007, Pages 428-435; (b) Tetrahedron, Volume 62, Issue 41, 9 October 2006, Pages 9610-9621; (c)J. Org. Chem., 2003, 68 (15), pp 6000–6004; (d) J. Org. Chem., 2001, 66 (26), pp 8944–8946; (e) J. Org. Chem., 2000, 65 (19), pp 5951–5955.

(3) Yu, Xiao-Qiang; Yamamoto, Yasunori; Miyaura, Norio:
Rhodium-Catalyzed Asymmetric 1,4-Addition of Heteroaryl Cyclic Triolborate to α,β-Unsaturated Carbonyl Compounds
Synlett 2009; 2009: 994-998

(4) Michael Shipman Aromatic heterocycles as intermediates in natural product synthesis. Contemp. Org. Synth., 1995, 2, 1-17

(5) Rafael Chinchilla Carmen Nájera, and Miguel Yus. Metalated heterocycles in organic synthesis: recent applications. ARKIVOC 2007 (x) 152-231.

(6) A.I. Meyers, Heterocycles in Organic Synthesis (General heterocyclic chemistry series) (1974) John Wiley & Sons Inc. ISBN-10: 0471600652, ISBN-13: 978-0471600657.