SHORT COMMUNICATION DOI: 10.1002/ejoc.200900337 Stereoselective Synthesis of Homoallyl Nitroalkane Derivatives through Base- Promoted Regioselective Decarboxylation of Baylis–Hillman Derivatives [‡] Maloy Nayak [a] and Sanjay Batra* [a] Keywords: Nitroalkanes / Regioselectivity / Baylis–Hillman / Decarboxylation / Allylic compounds The regioselective decarboxylation of nitroalkanoates syn- thesized from Baylis–Hillman acetates of acrylates proceeds stereoselectively to afford homoallyl nitroalkanes. In con- trast, nitroalkanoates derived from Baylis–Hillman acetates of acrylonitrile gave bisallyl nitroalkanes. Introduction Nitroalkanes are vital synthetic building blocks in or- ganic synthesis. The facile transformation of the nitro group into an amine, imine, hydroxylamine, or carboxylic acid group make the synthesis of a variety of nitroalkanes a sub- ject of constant study. [1] Nitroalkanes even allow efficient synthesis of fine chemicals in short sequences. [2] Primary nitroalkanes are reliable substrates for the generation of a variety of nitrile oxides as substrates for 1,3-dipolar cyclo- addition reactions. [3] The synthetic applications of Baylis–Hillman derivatives are paramount, as reflected from the recent literature. The most attractive feature of the product furnished by this C– C bond-forming reaction is the presence of three functional groups, which can be suitably modified for obtaining a plethora of heterocyclic scaffolds. [4] Our laboratory has dis- closed a number of general approaches for the synthesis of different aza-heterocyclic systems by using Baylis–Hillman derivatives. During the course of one such work, we discov- ered that the dialkanoates produced by the S N 2' reaction between ethyl nitroacetate and the Baylis–Hillman acetates upon treatment with base undergo decarboxylative proton- ation to afford homoallyl nitroalkanes containing a primary nitro group. Although the synthesis of allyl nitroalkanes bearing a primary nitro group has been achieved in Baylis– Hillman chemistry, [5] the synthesis of homoallyl nitroal- kanes bearing a primary nitro group from Baylis–Hillman adducts remains unreported (Figure 1). Decarboxylation [‡] CDRI Communication no. 7756 [a] Medicinal and Process Chemistry Division, Central Drug Research Institute, P. O. Box 173, Lucknow 226001, India Fax: +91-522-2623405, 2623938 E-mail: batra_san@yahoo.co.uk s_batra@cdri.res.in Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejoc.200900337. Eur. J. Org. Chem. 2009, 3505–3507 © 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 3505 (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) due to the presence of a nitro group on the α-carbon has literature precedence [6] and may be considered analogous to the decarboxylation experienced with α-keto acids or malo- nic acids under basic conditions. In the context of Baylis– Hillman chemistry, however, we have observed that a strong base is unable to effect the decarboxylation of α-keto acids or malonic acids. [7] Kim and co-workers very recently dem- onstrated that decarboxylative protonation can be achieved in Baylis–Hillman derivatives with the use of palladium salts for either obtaining 1,5-dicarbonyl compounds or con- ducting aralkylation. [8] During the course of this study, the identical reaction of nitroalkanoates afforded from Baylis– Hillman adducts of acrylonitrile unexpectedly produced bi- sallyl nitroalkanes. These new observations prompt us to report the findings of our study herein. Figure 1. Nitroalkanes from Baylis–Hillman chemistry. Results and Discussion At first, dialkanoates that served as the starting materials were prepared following the literature procedure. [9] Acetyl derivatives 1a–h and 2–4 of the Baylis–Hillman adducts were treated with ethyl nitroacetate in the presence of K 2 CO 3 in DMF to afford required compounds 5a–h and 6–8 (Scheme 1). Initially, treatment of 5a with NaOH in aqueous methanol led to consumption of the starting mate- rial within 8 h. Isolation and purification of the crude mate- rial furnished a product that was spectroscopically analyzed