Acetates allenes

The synthesis of allenes from organocopper compounds and acetylenic acetates was... 

The extracts were kept below 0°C (note 5). The combined extracts were washed with 5i acetic acid and subsequently dried over magnesium sulfate (note 6). The extract was concentrated in a water-pump vacuum to about 60 ml by means of the rotary evaporator, care being taken that the bath temperature remained below 25°C. The remaining pale yellow solution was warmed to about 35°C (internal temperature). The temperature rose gradually but was kept at about 45°C by occasional cooling. When after about 45 min the exothermic reaction had subsided, the flask was placed in a water-bath at 55°C. After 30 min the remaining pentane was removed in a water--pump vacuum. The orange residue, n 1.5878, yield aa. 92% was almost pure allenic dithioester. 

Didodecyldimetbylammonium bromide [3282-73-3] M 463.6, m 157-162 . Recrystd from acetone, acetone/ether mixture, then from ethyl acetate, washed with ether and dried in a vacuum oven at 60° [Chen et al. J Phys Chem 88 1631 1984 Rupert et al. J Am Chem Soc 107 2628 1985 Halpern et al. J Am Chem Soc 108 3920 1986- Allen et al. J Phys Chem 91 2320 1987]. 

Either pure acetoxyallene, on refluxing with the catalyst for 24 hr, equilibrates to an equimolar mixture of the two isomers. The mixture of allenes, if refluxed with acetic acid, rearranges to the 16,20-conjugated enol acetate ... 

Alkylallenes are obtained by the reaction of 1-ethynylcycloalkanol acetates with organocopper reagents, lithium dimethyl- and dibutylcuprates643 (see Section B.l). Even in the case of the presence of a substituent at the acetylenic terminus, SN2 displacement takes place, giving tetra-substituted allenes. Reaction of the steroidal 17-acetoxy-17-ethynyl derivative la shows that the... 

The reaction of propargylic chiral acetals with a catalytic copper reagent (RMgX/5% CuX) provides the expected alkoxy allenes in quantitative yield (Table 3)61. The diastereomeric excess is highly dependent on the size of the ring of the acetal and on the type of substituents it contains. The best diastereomeric excess is 85% with the acetal derived from cyclooctanediol. The use of lithium dimethylcuprate results in 1,2-addition lo the triple bond and the resulting lithium alkenyl cuprate bearing a cyclic acetal does not eliminate even at reflux temperature ( + 35°C). 

In contrast to the behavior of tetramethylallene, allene 38 undergoes central protonation in electrophilic additions. In an acetic acid sulfuric acid... 

The weaker Lewis add TMSOTf 20 as catalyst gives, after 2 h at 0°C in CH2CI2, a 20 80 mixture of 805 and 806 in only 23% yield (Scheme 6.8). But this yield will probably increase either on longer reaction time at 0°C or on shorter reaction time at 25 °C On replacing one of the methyl groups in 804 by an acetylene substituent the resulting enyne adds allyltrimethylsilane 82 or anisole in the presence of TMSOTf 20 to give allenes [18]. Substituted allyltrimethylsilanes such as 808 react with the allylic silylether 807 after 70 h at 25 °C in 62% yield to a 41 59 mixture of 809 and 810 as well as 7 [17]. Closely related additions of 82 to allylic ethers or O-acetates are discussed in Refs. 17a-c. 

Propargylic acetates, halides, and sulfonates usually react with a double-bond shift to give allenes.34 Some direct substitution product can be formed as well. A high ratio of allenic product is usually found with CH3Cu-LiBr-MgBrI, which is prepared by addition of methylmagnesium bromide to a 1 1 LiBr-Cul mixture.35... 

Oda et al. reported that under reflux conditions, the zinc-promoted reaction of 2,3-dichloro-l-propene with aldehydes and ketones in a two-phase system of water and toluene containing a small amount of acetic acid gave 2-chloroallylation products (Eq. 8.31).64 No conversion occurred when tin was used as the promoter. The absence of water completely shuts down the reaction. Interestingly, the action of 2,3-dichloropropene plus zinc powder in aqueous ethanol gives the dechlorination product, allene.65... 

An intramolecular Pd-catalyzed ring closure of an allylic halide, acetate or carbonate containing an allene moiety as 6/1-256, followed by a Suzuki reaction, was used by Zhang and coworkers for the synthesis of five-membered carbo- and heterocycles 6/1-257 and 6/1-258 (Scheme 6/1.67) [125]. 

Lauryl alcohol has been prepared by the reduction of the aldehyde with zinc dust and acetic acid 1 by the reduction of esters of lauric acid with sodium and absolute alcohol 2 or with sodium, liquid ammonia, and absolute alcohol 3 by the reduction of lauramide with sodium and amyl alcohol.4 The method in the above procedure is essentially that described by Levene and Allen.5... 

Additional hypotheses concerning prostaglandin biosynthesis in P. homomalla resulted from isolation of 11R-HETE (76) from the polar lipid fraction [95]. Apparently, 11R-HETE (76) is also a minor product of incubations of arachidonic acid with acetone powder preparations of P. homomalla [95], In this alternate hypothesis (Scheme 8), an 11-hydroxy or 11-hydroperoxy-8,9-allene oxide intermediate is formed from a sequence of oxidations at C8 and Cll. Opening of the allene oxide to a transient C8 earboeation induces eycli-zation with a consequent addition of water to C15. This proposed pathway leads initially to formation of PGE2 (16 or 38), which following acetylation, elimination of acetic acid from Cl 1-12, and esterification, forms the observed major natural product in the coral, 15-acetoxy methyl PGA2 (36 or 54). Notably, if... 

Diazomethane in the presence of palladium acetate gave with allenes 613 a similar mixture of methylenecyclopropanes 614 and spiropentanes 615. In contrast to Simmons-Smith reagent, diazomethane prefers to add to the less substituted allenic double bond (Scheme 87) [162]. 

A ring opening reaction of (1-lactams promoted by methoxide generated nitrogen nucleophiles in situ that subsequently added to proximal allenes producing trisubstituted pyrroles <06CC2616>. In the event, treatment of (3-lactam 3 with MeONa led to pyrrole-2-acetic ester 4 after cleavage of the amide bond, 5-exo-dig cyclization, and loss of methanol. The sequence was notable as no metal catalyst was required. 

Bis(tributyltin)oxide in antifouling paint was found to change to tributyltin chloride and an unknown organotin species by Allen and coworkers106. The organotin species appear to be held strongly within the paint film. In the case of triphenyltin chloride and triphenyltin acetate, evidence of dephenylation to form diphenyltin and monophenyltin compounds has been obtained. 

An allene moiety can serve as a nucleophile vis-a-vis a 7r-allylpalladium species generated from an allylic acetate moiety in substrates such as 495 (Scheme 124). The cyclization involving these two moieties generates another 7r-allyl intermediate, and the stage is set for the subsequent carbonylative cascade process as demonstrated by the transformation of 495 to 496.402... 

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