1,2-Allenyl esters, reaction with

The conjugate addition reactions of a-aminoalkylcuprates (derived from r-butoxy-carbonyl protected amines) with Q, /3-/3,y-allenyl esters occurs with preferred approach from the side opposite the substituent on the 4-position and results in trans alignment of the respective groups about the unconjugated double bond on the 1,4-adduct (Scheme 11). ... 

Intermediates such as 224 resulting from the nudeophilic addition of C,H-acidic compounds to allenyl ketones such as 222 do not only yield simple addition products such as 225 by proton transfer (Scheme 7.34) [259]. If the C,H-acidic compound contains at least one carbonyl group, a ring dosure is also possible to give pyran derivatives such as 226. The reaction of a similar allenyl ketone with dimethyl mal-onate, methyl acetoacetate or methyl cyanoacetate leads to a-pyrones by an analogous route however, the yields are low (20-32%) [260], The formation of oxaphos-pholenes 229 from ketones 227 and trivalent phosphorus compounds 228 can similarly be explained by nucleophilic attack at the central carbon atom of the allene followed by a second attack of the oxygen atom of the ketone at the phosphorus atom [261, 262], Treatment of the allenic ester 230 with copper(I) chloride and tributyltin hydride in N-methylpyrrolidone (NMP) affords the cephalosporin derivative 232 [263], The authors postulated a Michael addition of copper(I) hydride to the electron-... 

A fundamentally different approach to the synthesis of 3-pyrrolines is evidenced in the annulation in Eq. 13.50 [58]. Ethyl 2,3-butadienoate 150 reacts with N-sulfony-limine 151 in the presence of triphenylphosphine under very mild conditions to give JV-protected 3-pyrroline 152 in 90% yield. The mechanism that has been postulated is related to that of the Baylis-Hillman reaction. Michael addition of triphenylphosphine to the allenyl ester generates a zwitterion that combines with the imine to give 153 in a non-concerted process. This is followed by ring closure, proton exchange and expulsion of triphenylphosphine to give 152. This annulation is successful only for aromatic or cinnamyl imines [59]. 

In spite of these first successful results, so far Stille cross-couplings have rarely reported employing functionalized stannylated allenes such as easily available donor-substituted allene 80a or allenyl esters such as 81 (Scheme 14.19) [19, 41, 42]. A single palladium-catalyzed annulation reaction with 80b as precursor leading to an a-pyrone derivative was reported [43],... 

Type III reactions proceed by attack of a nucleophile at the central sp carbon of the allenyl system of the complexes 5. Reactions of soft carbon nucleophiles derived from active methylene compounds, such as /i-kcto esters or malonates, and oxygen nucleophiles belong to this type. The attack of the nucleophile generates the intermediates 9, which are regarded as the palladium-carbene complexes 10. The intermediates 9 pick up a proton from the active methylene compound and n-allylpalladium complexes 11 are formed, which undergo further reaction with the nucleophile, as expected, and hence the alkenes 12 are formed by the introduction of two nucleophiles. 

The allenyl esters formed by the carbonylation undergo an intramolecular ene reaction when an olefinic bond exists in a suitable position [12]. A particularly facile ene reaction is observed with these propargyl carbonates having an ester group attached to the triple bond. 

Reaction of 1,2-allenyl esters and 1, catalyzed by potassium carbonate, gave 456a through a tandem nucleophilic addition-lactoniza-tion process (06S2731). The (chlorocarbonyl)phenyl ketene was condensed with 1 to give 456 (R = Ph) (04T5931). 

Other variations of the [3 + 2] cycloaddition chemistry involving either SO2 or a S2O equivalent have been explored (Scheme 47). Iron allenyl complexes undergo reaction with SO2 to give either vinyl iron (105) or (106), depending on the substitution pattern. A propargylic iron complex reacts in a similar manner to give (107), but reacts with a cyclic thiosulfinate ester to give (108). 

Dimethyl malonate derivatives containing an allenyl sulfone substituent at the y- or 3-position undergo endo-mode ring closure to give cyclopentene or cyclohexene derivatives upon treatment with 1.5 equiv of t-BuOK in t-BuOH at rt. The intermediate unsaturated cycloadducts undergo demethoxycarbonylation and double bond isomerization under the reaction conditions (eq 53). Other active methine compounds behave similarly. A threefold excess of i-BuOK is more effective than certain amine bases for the conversion of phenylsulfonyl methyl derivatives of aromatic or heteroaromatic compounds into the corresponding dithio esters upon reaction with an excess of elemental sulfur. ... 

Insertion Reactions. Trimethylsilyldiazomethane undergoes net insertion between the B-C bond of borinate and boronate esters. Thus, olefin hydroboration, followed by treatment with TMSCHN2, oxidation, and desilylation offers a method for hydroxymethylation of alkenes in fair to moderate yield (eq 54). Stable, chiral allenylboranes (IR and IS) are prepared by reaction of TMSCHN2 with 5-MeO-9-BBN followed by resolution with pseudoephedrine and reaction with allenyl magnesium bromide (eq 55). Compounds IR and IS are useful for the asymmetric allenylboration of aldehydes with predictable absolute stereochemistry. The precursors to 1 are then readily recovered during work-up. ... 

Synthesis of S yn-jfi-hydroxy-a-vinyl hydroxyl esters in 68-91% yields with excellent diastereoselectivities >40 1 and with 73-89% ee has been achieved via aldol reactions of aldehydes with [(lO l-O-KlAl-l-ethoxybuta-TS-dienoxy]-9-borabicyclo[3.3.2]decan-10-yl]-trimethyl-silane that is generated in situ by kinetically controlled 1,4-hydroboration of allenyl ester with lO-trimethylsilyl-9-borabicyclo [3.3.2]decane." ... 

Scheme 6.24 Reaction with allenyl boronic ester.

Propargylic esters 67 have been studied extensively in ttansition-metal catalysis [35]. Recently it has been found that these compounds were effectively converted to useful molecular skeletons by interaction with -ir-acidic metal catalysts. These reactions proceed via initial 3,3-rearrangement, leading to allenyl ester intermediate 68 or 1,2-acyloxy rearrangement to metal carbenoid intermediate 69 (Scheme 27.25). These rearrangement reactions have been extended to the corresponding phosphates and sulfonates. 

Allenyl and 1- and 2-alkynyl sulfoxides have also been prepared by reaction of organomagnesium halides with sulfinate ester 19. 1-Alkynyl p-tolyl sulfoxides were prepared in good yield from 1-alkynylmagnesium halides plus ester 19 in toluene (equation ll)63. The corresponding organolithium compound was unsatisfactory as a... 

The competition between a propargylic ether and a teriary propargyhc amine provided an allenyl ether rather than an allenylamine [182], The reaction was also successful with propargyl allyl ethers [232]. An additional ester group in the propargylic position is tolerated [233], and consequently the reaction also works with esters of propargyhc alcohols [234—236]. In the past 4years, several derivatives of carbohydrates were converted successfully [217, 237-241] two examples are the isomeriza-tions of enantiomerically pure 98 [242] and 100 [217, 243] (Scheme 1.43). 

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