A convenient, rapid, and general synthesis of a-oxo thiocyanates using clay supported ammonium thiocyanate H.M. Meshram ⇑ , Pramod B. Thakur, B. Madhu Babu, Vikas M. Bangade Organic Chemistry Division-I, Indian Institute of Chemical Technology, Hyderabad 500 007, India article info Article history: Received 29 November 2011 Revised 24 January 2012 Accepted 25 January 2012 Available online 3 February 2012 Keywords: Clay supported ammonium thiocyanate a-Oxo thiocyanates Solvent-free reaction Catalyst-free reaction Green synthesis abstract A very rapid, convenient, and general method for the synthesis of a-oxo thiocyanates has been described by using clay supported ammonium thiocyanate. The procedure avoids the use of additional catalyst, sol- vent, aqueous work-up and the yields are high. Moreover, the method is applicable for a variety of aryl, heteroaryl, alkyl a-halo carbonyls, b-keto tosylates, a-halo b-dicarbonyl, a-tosyl, b-dicarbonyl, alkyl halide, and alkyl tosylates. Ó 2012 Elsevier Ltd. All rights reserved. Thiocyanate compounds have attracted great attention as inter- esting intermediates due to its easy transformation into highly valuable molecules applied to heterocyclic chemistry. These com- pounds possess a broad spectrum of biological activities such as anticancer, insecticides, antiasthmatic, DNA topoisomerase inhibi- tors, 1 and also found in some biologically active natural products 2 (Fig. 1). Additionally, thiocyanato functionality can be used as a masked mercapto group or as a precursor for sulfur-containing heterocyclic compounds, such as thiazolidine, cyclic thioureas, and thiazoles 3 which exhibit important biological activities. 4 Thus the synthesis of different thiocyanate compounds is desirable in the view of organic and medicinal chemistry researchers. Several methods have been reported for the preparation of a- oxo thiocyanates which include the oxidative thiocyanation of silyl enol ethers with hypervalent iodine-lead (II) thiocyanate reagent and task-specific ionic liquids containing SCN as a counterion. 1 KSCN 2,5 or TMSNCS 6 in the presence of organic solvents have been utilized for thiocyanation. The a-thiocyanation of enolizable ke- tones also reported by using NH 4 SCN in the presence of I 2 , 7 FeCl 3 , 8 BDMS, 9 NBS, or DEAD. 10 Recently, TBAB 11 in aqueous media, ionic liquid brush, 12 and Amberlite IRA-910 13 with thiocyanate counter ion has been used for the synthesis of phenacyl thiocyanates. The transformation of thiols to thiocyanates employing a Ph 3 P/Br 2 / NH 4 SCN mixture 14 and transformation of alkenes to thiocyanates with CAN/NH 4 SCN 15 is also documented. In an alternate method, acyl isothiocyanate has been employed as an efficient thiocyanate transfer reagents with N-methylimidazole. 16 However, many of these methods involve the use of, toxic metal thiocyanates, expen- sive thiocyanating agents, a large excess of strong oxidizing agents, organic and hydroalcoholic reaction media, 17 and also require longer reaction time. Moreover some of the reagents promote the isomerization of thiocyanate to isothiocyanate in solution at tem- peratures above 50 °C and/or in acidic conditions. 1,7,18 In this con- text, the development of solvent free, mild, and rapid synthesis of thiocyanate derivatives in high yields is desirable. In recent years, sustainable processes are highly in demand in the chemical industry. 19 The ‘process efficiency’ concept is not only related to a high chemical yield, but also to minimize the use of large amounts of harmful organic reagents, solvents, catalyst, and undesired chemical waste. 20 Lewis acid catalysis has attracted con- siderable attention in heterogeneous catalysis. 3,21 During the past decades solid supported reagents have been exploited extensively for the development of environmental friendly reaction. 22 Among these, clay supported catalysts provide an easy separation of the products from the reaction without tedious aqueous work-up 0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2012.01.113 ⇑ Corresponding author. Fax: +91 40 27193275. E-mail address: hmmeshram@yahoo.com (H.M. Meshram). H H SCN Carvernothiocyanate NCS H H 4-Thiocyanato-9-cadinene H SCN 2-Thiocyanatoneopupukeanane Figure 1. Representative examples of natural product containing thiocyanato structural motifs. Tetrahedron Letters 53 (2012) 1780–1785 Contents lists available at SciVerse ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet