With nitro-ketones

Nitroparaffins add 1,4 to conjugated systems methyl vinyl ketones, for example, yield the corresponding y-nitro ketone, which can be reduced to a y-nitro alcohol (48). More than one vinyl group may react with primary nitroparaffins (49). 

The required nitro compounds are easy to prepare, and are useful building blocks for synthesis. Treatment with an appropriate base—e.g. aqueous alkali—leads to formation of nitronates 2. Various substituted nitro compounds, such as nitro-ketones, -alcohols, -esters and -nitriles are suitable starting materials. 

Nitradon of the potassium enolates of cycloalkanones with pentyl n silyl enol ethers with nitroniiim tetraflnoroborate " provides a method for the preparadon of cydic ct-nitro ketones. Tnflnoroacetyl nitrate generated from tnflnoroacedc anhydnde and ammonium nitrate is a mild and effecdve nitradug reagent for enol acetates fEq. 2.411. ... 

Cyclic and acyclic silyl enol ethers can be nitrated with tetranitromethane to give ct-nitro ketones in 64-96% yield fEqs. 2.42 and 2.43. " The mechanism involves the electron transfer from the silyl enol ether to tetranitromethane. A fast homolydc conphng of the resultant cadon radical of silyl enol ether with NO leads tn ct-nitro ketones. Tetranitromethane is a neutral reagent it is commercially available or readdy prepared. " ... 

A novel one-pot synthesis of ct-nitro ketones from alkenes has been observed 01 with trimethylsilyl nitrate-chromium trioxide or a trimeihylsilyl nitrate-DMSO reagent system fEq. 2.44. ... 

Conjugate dcLiicii of nkro ilkdnes to illyl Baylis-Hillman acetates in the pesence of NaOH (0.6 N in THF ves 2-alkylidene-4-nitro ketones with high sieteoselecdvity these are convened via the Nef teacdon into the conesponding 1,4-diketones fEq. 4.1... 

The condensation of nitro ilkenes with enamino- ketones or enamino-esters CGrob-Camenisch reacdoni has been v/idely used for pyrrole synthesis fEq. 10.4. This process is now carried out v/ith resin-boiind enamino-ketones for combinatoriM syntheses of pyrroles. ... 

In contrast, the tin(Il) enolates of cyclohexanone undergo addition to (2f)-(2-nitroethenyl)ben-zene to give 2-(2-nitro-l-phenylethyl)cyclohexanones with high anti diastereoselection5. The analogous reactions with cyclopentanone and 4-tert-butylcyclohexanone were less diastereose-lective with anti/syn ratios of 70 30 and 62 38. respectively. Modest to excellent diastereoselec-tivity was observed with acyclic ketones (d.r. 75 25 to 90 10) however the precise stereochemical details were not provided. 

The radical alkylation of ketones is achieved by their conversion into the desired N-silyloxy enamines 81 (Scheme 13). The reaction of 81 with diethyl bromomalonate in the presence of EtsB (0.5 equiv) in benzene was performed in open air and stirred at room temperature for 3h. With nitro compounds it is achieved by their conversion into the desired ]V-bis(silyloxy)enamines (82) (Scheme 13). When the reaction is carried out with 82 and alkyl iodides with an electron-withdrawing substituent at the a-position, using V-70 as radical initiator (2,2 -azobis(4-methoxy-2,4-dimethylvaleronitrile)), it underwent a clean radical alkylation reaction to yield an oxime ether. Successful radical alkylation of... 

Nitration of ketones or enol ethers provides a useful method for the preparation of a-nitro ketones. Direct nitration of ketones with HN03 suffers from the formation of a variety of oxidative by-products. Alternatively, the conversion of ketones into their enolates, enol acetates, or enol ethers, followed by nitration with conventional nitrating agents such as acyl nitrates, gives a-nitro ketones (see Ref. 79, a 1980 review). The nitration of enol acetates of alkylated cyclohexanones with concentrated nitric acid in acetic anhydride at 15-22 °C leads to mixtures of cis- and rrans-substituted 2-nitrocyclohexanones in 75-92% yield. 4-Monoalkylated acetoxy-cyclohexanes give mainly m-compounds, and 3-monoalkylated ones yield fra/w-compounds (Eq. 2.40).80... 

The nitro group of a-nitro ketones is readily removed either by treatment with Bu3SnH89 or reduction with LiAlH4 of the corresponding tosylhydrazones (Eq. 3.58).90 Details of denitration are discussed in Section 7.2, and some applications of this process are shown in Schemes 3.5-3.7. 

Conjugate addition of nitroalkanes to ailyl Baylis-Hillman acetates in the presence of NaOH (0.6 N) in THF gives 2-alkylidene-4-nitro ketones with high stereoselectivity these are converted via the Nef reaction into the corresponding 1,4-diketones (Eq. 4.119).164... 

The Michael addition of cyclic a-nitro ketones to acrolein or methyl vinyl ketone followed by reduction of the carbonyl group and treatment with base results in the ring expansion (Eq. 

Dianions derived from cyclic a-nitro ketones have been used for the preparation of the natural product phoracanthlide and related macrocyclic lactones (see Scheme 5.2).13 Alkylation of dianion of a-nitro cyclic ketones is followed by radical denitration with Bu3SnH (see Section... 

The acylation of the carbanions derived from nitroalkanes with acyl imidazoles or alkoxy-carbonylimidazoles takes place at the carbon atom to yield a-nitro ketones or a-nitro esters, respectively (Eq. 5.10).21 The lithium salts of nitroalkanes were isolated and used in THF or DMSO in the original procedure. Later, potassium salts generated in situ on treatment with r-BuOK in DMSO are reactive enough to give a-nitro ketones in good yield (Eq. 5.11).22... 

As the nitro group is removed by radical denitration with Bu3SnH, allylic alkylation of a-nitro ketones with allyl carbonates in the presence of Pd(0) followed by denitration with Bu3SnH provides a new regio-selective allylation of ketones under neutral conditions (Eq. 5.55).79... 

Enantioselective allylations of a-nitro ketones and a-nitro esters with allyl acetates are carried out in the presence of 2 equiv of alkali metal fluorides (KF, RbF, CsF) and 1 mol% palladium catalysts prepared in situ from Pd2(dba)3-CHC13 and chiral phosphine ligands. Moderate enantio-selectivity (ca 50% ee) is reported for allylation of cx-nitroketones (Eq. 5.60). The highest selectivity (80% ee) is observed for allylation of the reaction of tert-butyl ester (Eq. 5.61).93... 

Primary nitro ketones, ethyl nitroacetate, and (phenylsulfony l)nitromethane react with alkenes in the presence of Lewis acids to give nitrile oxide cycloaddition.61a Similarly, the reaction of a-nitro ketones with TeCl4 generates the corresponding nitrile oxides, as shown in Eq. 6.36.61b... 

The reduction of y-nitroketone acetals as in Eq. 6.50 with ammonium formate in the presence of Pd/C gives the corresponding amines in good yields. However, the reduction of y-nitro ketones are reduced to cyclic nitrones (Eq. 6.51).97 This reduction is far superior to the classical method using Zn/NH4C1 due to improved yield and simple workup. 

The reduction of nitro ketones with baker s yeast is a good method for the preparation of chiral nitro alcohols.89 The reduction of 5-nitro-2-pentanone with baker s yeast gives the corresponding (5)-alcohol, which is an important chiral building block. Various chiral natural products are prepared from it. In Scheme 7.16, the synthesis of the pheromone of Andrena haemorrhoa is described, where the acylation of the chiral nitro alcohol followed by radical denitration is involved as key steps.89a... 

Rawal and Kozmin have utilized a Reissert type reaction in the total synthesis of tabersonine. The requisite nitro ketone is prepared by SNAr reaction of o-nitrophenylphenyliodonium fluoride with ketone silyl enol ether (Scheme 10.10).96... 

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