Of fi-nitro alcohol

The nitro-dldolredcdon between nitrodlkdnes and carbonyl compounds to yieldfi-nitro alcohols was discovered in 1895 by Henry. Since dien, diis reaction has been used extensively in many important syndieses. In view of its significance, diere are several reviews on die Henry reaction." These reviews cover syndiesis of fi-nitro alcohols and dieir applications in organic synthesis. The most comprehensive review is Ref 3, which summarizes the literature before 1970. More recent reviews are Refs. 4 and 5, which summarize literatures on the Henry reaction published until 1990. 

Dehydration of fi-nitro alcohols using DCC gives a mixnire of E/Z nitroaikenes. The pure fE -isomers are obtained on treatment with catalytic amounts of triethylamine or polymer-bound triphenylphosphme (TPP fEq. 3.281. When (Z) nitroaikenes are desired, the addition of PhSeNa to the E/Z mixnire and protonadon at -78 "C fohowed by oxidadon with gives fZi-nitroalkenes fEq. 3.29. ... 

The reduction of fi-nitro alcohols v/ith ammonium formate in the presence of Pd/C also proceeds v/ith retendon of their configuradons fEq. 6.53. ... 

The reducdon of fl-rdtro alcohols v/ith LLAiH) residts in low yields of fl-amino alcohols due to the occurrence of a retro-aldol reacdon. This problem is resolved by protecdng of OH of fi-nitro alcohols, as shovm in Eq. 6.53. ... 

The synthedc ndlity of the Henry reaction is shovm in Scheme 3.1, where fi-nitro alcohols are converted into fi-amino alcohols, amino sugars, ketones and other important compounds. 

A more effecdve catalyst for the Hetuy reacdon is a polymer-supported base such as amberlyst A-31. Various fi-nitro alcohols can be obtained v/ith the help of amberlyst v/ith or without solvent fEq, 3,14, A recent report claims that amberlite IRA-430 COH-formi or DOWEX-1 COH-formi is more effecdve for the Henry reacdon than amberlyst A-31/ Poly-... 

Another method for improving the reactivity of nitro compounds is provided by the double deprotonadon of nitroalkanes. In this case, the reacdon with ketones affords fi-nitro alcohols in 4Q-6Q% yield CEq.d.lQi ... 

Conjugated nkro ilkenes are isomerized to illylic nitro compounds under basic conditions Reactions of a,fi-unsarurated nitro compounds with aldehydes under basic conditions lead directly to y, 5-unsaturated fi-nitro alcohols fEq 3 24 "This reaction is very useful for preparing illyhc nitro compounds... 

An experimentally simple ptocedure for stereoselecdvely preparing fi-nitro alcohols has been developed. The alkyl nitronates, formed by the acdon of u-butyUithiumonnitroalkanes in THF soludon, react v/ith aldehydes in the presence of isopropoxydtanium trichloride at room temperanire to give the fi-nitro alcohols enriched in the ruiri-thastereoisomers fEq. 3.711. 

Jdger and co-workers have prepared various amino sugars by the reduction of the con sponding fi-nitro alcohols with H-, and Pd/C, as exemplified in Eq 6 49 fsee Chapter 3 ... 

Stereoselective preparation of CEi-allyl alcohols via radical elimination from ruin -y-phenylthio-fi-nkro alcohols has been reported. The requisiteruin -fi-nitro sulfides are prepared by protonadon of nitronates at low temperanire Isee Chapter 4, and subsequent treatment v/ith Bu-vSnH induces and eliminadon to givelE -alkenes selecdvely IseeEq. 7.112. Unfortunately, it is difficult to get the pure syu-fi-nitro sulfides. Treatment of a rruxnire of syu- and ruin -fi-nitrosulfides v/ith Bu- SnH results in formadon of a rruxnire of (Ey and lZ -alkenes. 

Lithiation of the methyl of (methylthio)benzene followed by acylation with an acyl chloride and acidification to pH 4-5 yields benzothiophene in good yields, but when aroyl chlorides are used, the mixture has to be heated in benzene. An attempted dehydration of the secondary alcohol (87.4) with hydrobromic acid led to S-demethylation and cyclization. Similar treatment of the isomeric 2-(2-methy thio-4-nitrophenyl)-l-phenylethanol gave a high yield of 6-nitro-2-phenyl-2,3-dihydrobenzo[fi]thiophene [2653]. 

If this limited sample of spectra of hydroxynitrates is representative of other fi-nitro-substituted alcohols, then the photodecomposition of these species within the troposphere is expected to be unimportant, since there is little or no overlap of the absorption region with that of the actinic flux available within the troposphere. 

Polynitroaliphatic alcohols containing nitro groups on the carbon fi to the hydroxy functionality are less basic than their alkyl counterparts. This decreased basicity of the hydroxy group makes reactions such as esterification, acetal formation and alkylation much slower than usual, and in some cases, these reactions may not proceed without catalysts. To add to the problem, normal base catalysts cannot be used in conjunction with 2,2-dinitroalkanols and l,l,l-trinitro-2-alkanols because of their facile dissociation in alkaline solution. 

---