5- Hydroxy-4-octanone

Prominent volatiles related to "grassy" flavor of lamb according to Suzuki (34) were hexanal, heptanal, 2,3-octanedione, 2,4-hepta-dienal, 3-hydroxy-2-octanone, 2-nonenal, 2-decenal, 2,4-decadienal,... 

Japanese cedar (Cryptomeria japonka) Anaj lyptus subjiisciatus Methyl Phenyl Acetate (R)-3-hydroxy-2-hexanone, (R)-3-hydroxy-2-octanone [222]... 

Unprotected a-hydroxy ketones appear to favor chelation control with most reagents. In an early study 3-hydroxy-2-octanone was treated with a range of aluminum hydride reagents to give mixtures of anti- and syn-2.3-octanediol in which the former predominated13. However, the degree of selectivity was rather modest. Several other substrates behaved similarly (Table 3)13,14. 

Out first example is 2-hydroxy-2-methyl-3-octanone. 3-Octanone can be purchased, but it would be difficult to differentiate the two activated methylene groups in alkylation and oxidation reactions. Usual syntheses of acyloins are based upon addition of terminal alkynes to ketones (disconnection 1 see p. 52). For syntheses of unsymmetrical 1,2-difunctional compounds it is often advisable to look also for reactive starting materials, which do already contain the right substitution pattern. In the present case it turns out that 3-hydroxy-3-methyl-2-butanone is an inexpensive commercial product. This molecule dictates disconnection 3. Another practical synthesis starts with acetone cyanohydrin and pentylmagnesium bromide (disconnection 2). Many 1,2-difunctional compounds are accessible via oxidation of C—C multiple bonds. In this case the target molecule may be obtained by simple permanganate oxidation of 2-methyl-2-octene, which may be synthesized by Wittig reaction (disconnection 1). 

Diacetates of 1,4-butenediol derivatives are useful for double allylation to give cyclic compounds. l,4-Diacetoxy-2-butene (126) reacts with the cyclohexanone enamine 125 to give bicyclo[4.3.1]decenone (127) and vinylbicy-clo[3.2.1]octanone (128)[85,86]. The reaction of the 3-ketoglutarate 130 with cij-cyclopentene-3,5-diacetate (129) affords the furan derivative 131 [87]. The C- and 0-allylations of ambident lithium [(phenylsulfonyl)methylene]nitronate (132) with 129 give isoxazoline-2-oxide 133, which is converted into c -3-hydroxy-4-cyanocyclopentene (134)[S8]. Similarly, chiral m-3-amino-4-hyd-roxycyclopentene was prepared by the cyclization of yV-tosylcarbamate[89]. 

ACYLOIN CONDENSATION BY THIA20L1UN ION CATALYSIS BUTYROIN (4-Octanone, 5-hydroxy-I... 

IN SITU GENERATION OF ACYLLITHIUM REAGENTS a-HYDROXY KETONES FROM KETONES 3-HYDROXY-2.2.3-TRIMETHYLOCTAN-4-0NE FROM PINACOLONE (4-Octanone, 3-hydroxy-2,2,3-trlmethyl-)... 

Hexanone, 2-heptanone, 2-octanone, 2-nonanone, 6-methyl-5-hepten-2-one, fenchone, carvone, acetophenone, 2-hydroxy-4,6-dimethoxy-5-methylacetophenone... 

Yamamoto and Maruoka demonstrated that ATPH can discriminate between structurally similar aldehydes, thereby facilitating selective functionalization of the less-hindered aldehyde carbonyl [163]. Treatment of an equimolar mixture of valeralde-hyde (149) and cyclohexanecarbaldehyde (150) with ATPH (1.1 equiv.) in CH2CI2 at -78 °C, then addition of Danishefsky s diene gave hetero-Diels-Alder adduct 151 and 152 in the ratio > 99 1. It is worthy of note that the complexed aldehyde could react with the diene only. The reaction gave relatively low chemoselectivity with other types of Lewis acid (ratio of 1517152 6.2 1 with (Pr 0)2Ti2Cl2 5 1 with McsAl 3.7 1 with MAD 2 1 with TiCU 1.3 1 with BF3-OEt2). This emphasizes that the cavity of ATPH plays an important role in differentiating between the reactivities of the two different aldehydes. In a similar manner, the aldol reaction of a mixture of 149 and 150 was effected with ATPH to furnish 4-hydroxy-2-octanone (153) without formation of 154 (Sch. 122). 

The results of Barltrop and Coyle , on the photolysis of aliphatic ketones in solution at 3130 A, support the explanation suggested by Wagner and Hammond for the low quantum yields. The overall quantum yield for disappearance of 2-pentanone, 2-octanone and 5-methyl 2-octanone was found to increase and approach unity in hydroxylic solvents. This increase can be attributed to the solvation of the hydroxy biradical intermediate. Since, however, the solvent effect was not observed for products originating from excited singlet molecules, it is probably only the triplet state which decomposes via biradicals. 

Diiodonickel (1 mol%) accelerated significantly many of the reductions performed by Sml2 in THE For example, some epoxides were deoxygenated in good yields to the corresponding alkenes at room temperature in 20 min, 2-octanone gave the pinacol in 10 min (instead of 24 h without catalyst) at room temperature, and cyclohexane carbonyl chloride coupled quantitatively into 2-hydroxy-1,2-dicyclohexylethanone in 1 min (reaction performed in THP). 

The use of microorganisms other than baker s yeast can be advantageous. While baker s yeast reduction of 2,3-octanedione leads to a mixture of (S)-2-hydroxy-3-octanonc, the isomeric ketol, (3S)-3-hydr0xy-2-octanone and the (25,3/ )-2,3-octanediol, reduction with the fungus Beauveria sulfurescens gives only (25,3S)-2,3-octanediol in enantiomerically pure form222. 

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