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Enediones containing a variety of substituents in the 1,5-positions are formed in good yields by the reaction of methyl ketone enolates, generated with potassium tert-butoxide, with -oxoketene dithioacetals, the latter being prepared from alkyl, cycloalkyl, aryl, or heteryl methyl ketones, NaH, CS2, and CH3I. Ring closure of the 1,5-enediones with NH4OAc gave 2,6-disubstituted 4-(methylthio)pyridines in good to excellent yields. This procedure is particularly suited for the synthesis of 2,6-diheterylpyridines and provides a simple synthesis of terpyridinyl and other oligopyridines. The methylthio groups in the -oxoketene dithioacetals may be oxidized to the mono-and disulfoxides with m-chloroperbenzoic acid, but with excess peracid, in addition to oxidation to the disulfone, epoxidation of the double bond also occurs. The pyridine 4-methylthio substituent may also be oxidized to the sulfoxide and to the sulfone, and the latter may be displaced with cyanide ion to form the corresponding 4-carbonitrile.Numerous methods for the synthesis of a wide variety of substituted pyridines have been described1 2 in the lit-yco, cm"1 c6h5 90-92® 58 yellow needles'1 C"H12OS, 224 (42) 1610 4-CH3OC6H4 98-99® 61 yellow needles'1 c12h1403s3 254 (36) 1595 2-CsH4N 110-111 71 yellow prisms C10H,,NOS2 225(2) 1625 2-C4H30 114-115

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High-throughput and area-efficient designs of hash functions and corresponding mechanisms for Message Authentication Codes (MACs) are in high demand due to new security protocols that have arisen and call for security services in every transmitted data packet. For instance, IPv6 incorporates the IPSec protocol for secure data transmission. However, the IPSec's performance bottleneck is the HMAC mechanism which is responsible for authenticating the transmitted data. HMAC's performance bottleneck in its turn is the underlying hash function. In this article a high-throughput and small-size SHA-256 hash function FPGA design and the corresponding HMAC FPGA design is presented. Advanced optimization techniques have been deployed leading to a SHA-256 hashing core which performs more than 30% better, compared to the next better design. This improvement is achieved both in terms of throughput as well as in terms of throughput/area cost factor. It is the first reported SHA-256 hashing core that exceeds 11Gbps (after place and route in Xilinx Virtex 6 board).