Trifluoroacetoxy-phenylselenation of nitroolefins regioselective preparation of nitroallylic alcohol derivatives and their use as multiple coupling reagents

Abstract

It has been shown In previous papers that the pivalate of 2-nitro-2-propen-1-ol (NPP, 1 ), a nitroolefin with allylic leaving group, can be used as a versatile multiple coupling reagent. The present contribution describes the preparation of NPP analogues, substituted in the 1- and/or 3-position of the allylic carbon skeleton. Standard methods of nitroaliphatic chemistry readily provide symmetrically substituted derivatives such as the cyclohexenes ( 7 ) and the indenes ( 8 ), while unsymmetrical ones such as the phenyl NPP 9 are not so easy to prepare. This situation is now greatly improved by a regioselective method of introducing an allylic pivaloyloxy group into nitroolefins: in the first step of the four-step sequence a phenylseleno- and a trifluoroacetoxy-group are added across the nitroolefinic double bond ( 10 → 11 ), then, the trifluoroacetate is cleaved, and tne resulting nitro-phenylseleno-alcohol 12 is oxidized with elimination to the nitroallylic alcohols 13 . These are pivalated by pivalic anhydride/ BF 3· etherate (→ 14 ). - The regioselective preparation of the products 16 – 34 of nitroallylation of various nucleophiles with substituted NPP-type reagents demonstrates the broad scope of these multiple coupling reagents. Due to the multitude of conversions of the nitro group, these reagents provide access to a great variety of structures without NO 2 -substituents, cf. 2 and 3 . The mechanism of the reaction of NPP-derivatives is discussed.