Allene-aldehyde/ketone

C=CHCH2NAtN=CR has been reported. " Propargylic vinylic compounds give allenic aldehydes, ketones, esters, or amides ... 

The nucleophilic attack on an acceptor-substituted allene can also take place at the acceptor itself, especially in the case of carbonyl groups of aldehydes, ketones or esters. Allenic esters are reduced to the corresponding primary alcohols by means of diisobutylaluminum hydride [18] and the synthesis of a vinylallene (allenene) by Peterson olefination of an allenyl ketone has also been reported [172]. The nucleophilic attack of allenylboranes 189 on butadienals 188 was investigated intensively by Wang and co-workers (Scheme 7.31) [184, 203, 248, 249]. The stereochemistry of the obtained secondary alcohol 190 depends on the substitution pattern. Fortunately, the synthesis of the desired Z-configured hepta-l,2,4-trien-6-ynes 191 is possible both by syn-elimination with the help of potassium hydride and by anti-elimination induced by sulfuric acid. Analogous allylboranes instead of the allenes 189 can be reacted also with the aldehydes 188 [250]. 

The rearrangements of 3-methylbut-l-ene oxides" and l,2-epoxybut-3-ene on lithium phosphate have been studied, and a detailed theoretical study of the rearrangement of allene oxide (342) to cyclopropanone (344), which shows that the transformation proceeds via an intermediate oxyallyl (343), has been presented. It has been shown that aldehydes, ketones, and cyclic ethers are all produced... 

Metal complexes enable one to employ molecules that are thermally unreactive toward cycloadditions by taking advantage of their ability to be activated through complexation. Most of the molecules activated by transition-metal complexes involve C-C unsaturated bonds such as alkynes, alkenes, 1,3-dienes, allenes, and cyclopropanes. In contrast, carbonyl functionalities such as aldehydes, ketones, esters, and imines seldom participate in transition-metal-catalyzed carbonylative cycloaddition reactions. Recently, such a transformation was reported via the use of ruthenium complexes. 

The reaction can be extended to allene-aldehydes. Kang et al. [16] reported on the Ru3(CO)12-catalyzed cyclocarbonylation of allene-aldehydes or allene-ketones leading to a-methylene-y-butyrolactones (Eq. 6). The fact that a ketone moiety also functions as a two-atom unit indicates that the reaction includes metallacycle 5 as an intermediate. 

The C-H bond cleavage of active methylene compounds with a transition metal catalyst is another method for the functionalization of these C-H bonds. To date, several reactions have been developed. In particular, the asymmetric version of this type of catalytic reaction provides a new route to the enantioselective construction of quaternary carbon centers. One of the most attractive research subjects is the catalytic addition of active methylene C-H bonds to acetylenes, allenes, conjugate ene-ynes, and nitrile C-N triple bonds. The mthenium-catalyzed reaction active methylene compounds with carbonyl compounds involving aldehyde, ketones, and a,y3-unsatu-rated ketones and esters is described in this section. 

Danheiser, R. L., Carini, D. J., Kwasigroch, C. A. Scope and stereochemical course of the addition of (trimethylsilyl)allenes to ketones and aldehydes. A regiocontrolled synthesis of homopropargylic alcohols. J. Org. Chem. 1986, 51, 3870-3878. 

French workers have extensively explored type I intramolecular ene reactions of allenic aldehydes which give dienols. Thermolysis of aldehydes and ketones such as (158) affords ene adducts (159 42%, 150 C, 30 min), (160 75%, 150 "C, 60 min), (161 70%, 200 C, 15 min), (162 52%, 200 C, 60 min), (163 65%, 230 °C, 60 min) and (164). Lewis acid catalysis was investigated with limited success (Scheme 25). Comparison of yields and reaction times indicates that buttressing gem methyl groups and trisubstituted allenes facilitate the reaction, while use of ketones and formation of six- rather than five-membered rings retard it. 

Terminal allenes. Aldehydes and ketones can be converted into terminal allenes by the sequence formulated in equation (1). 

Coi ugated allenic aldehydes or ketones. Conjugated allenic aldehydes can be prepared in satisfactory yield by reaction of allenyllithium compounds with DMF (1.5 equiv.) in THF ( — 70°, 2 hours) (equation I). Conjugated allenic ketones are obtained when RCONfCHala is used in the reaction (equation II). 

The [(Ti-allyl)PdCl]2-catalyzed reactions of allene-aldehydes or -ketones 153 with Me3SiSnBu3 led to the cyclic 2-vinylic alcohols 155 via the formation of an aldehyde- or ketone-containing 2-trimethysilyl-2-alkenyl tin intermediate 154 (Scheme 63) [38]. In the presence of an aryl iodide, Pd2(dba)3 could catalyze the coupling cyclization of allene-aldehydes or -ketones 153 with Bu3SnSnBu3 leading to the cyclic 2-(r-arylvinyl) cyclic alcohols 156 stereoselectively with the cis isomer being the major product (Scheme 64) [39]. 

The same products can be prepared from the Pd-catalyzed reaction of allene-aldehydes or -ketones 153 with Arl in the presence of metallic indium (Scheme 65) [40, 41]. The cis stereoselectivity of these reactions was probably determined by the chairlike conformation of the intermediate 157 (Scheme 66). 

The B-allyl-9-BBN derivatives formed by hydroboration of allenes are utilized for addition of the allyl group to the carbonyl moiety of aldehydes, ketones, and other carbonyl derivatives (allylboration). Since allenes are easily prepared from corresponding olefins [12, 13], the route the olefin-allene-allylborane-carbonyl addition adduct is a general allylation procedure, which provides an attractive alternative to Grignard-based sequences for the syntheses of complex structures. 

Almost all the electrophilic groups or electrophilic intermediates can be employed as the hydride acceptors, e.g., alkylidene malonates, carbophilic transition metals activated alkynes or allenes, enal/enones, aldehyde/ketones, imines, ketenimine/car-bodiimides, metal carbenoids, alkynes carrying electron-withdrawing groups, as well as in situ-generated carbocations (Fig. 3). 

Oxidative Methods.—Oxidation of Alcohols. Benzoyl peroxide catalysed by nickel(ii) bromide gives high yields of aldehydes and ketones from the corresponding alcohols. Similar yields are obtained with t-butyl hydroperoxide catalysed by diaryl diselenides, a method particularly recommended for benzylic or allylic alcohols. Ketones are obtained from secondary alcohols using hydrogen peroxide catalysed by molybdenum or tungsten peroxo-complexes/ and nickel peroxide has been employed to prepare a-allenic aldehydes and ketones from allenic alcohols. ... 

Thermal rearrangement of a range of enynols (232) gives y-allenic aldehydes or ketones (233), together with their secondary rearrangement products. ... 

Different studies on coconut oil have identified hydrocarbons, alcohols, aldehydes, ketones and 5-lactones that have significant contributors to its aroma (Pai et al., 1970 Allen, 1965 Lin Wilkins 1970). 

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