Bicyclic allylic acetate

The synthesis of the bioactive natural product warburganal from (-)-sclareol was carried out by A.F. Barrero et al. The bicyclic allylic acetate was epoxidized and deacetylated under basic conditions. Next, the solution of the ketoepoxide in glacial acetic acid was treated with hydrazine hydrate and the resulting mixture was heated at reflux for 30 minutes to afford the bicyclic allylic did in excellent yield. 

For the bicyclic allylic acetate depicted below only moderate asymmetric induction is achievedl7. The small bidentate ligand Chiraphos gives better results than BINAP and Diop with respect to both enantio- and regioselectivity. 

This rearrangement of allylic acetals can also be used for furan annelations, in which the formation of the new tetrahydrofuran ring is coupled with ring enlargement of the starting ring.3 The same dr-fused bicyclic tetrahydrofuran is formed from either one of the cis- or mwr-allylic diols used as starting materials. 

A masked allylic boron unit can be revealed through a transition-metal-catalyzed borylation reaction. For example, a one-pot borylation/allylation tandem process based on the borylation of various ketone-containing allylic acetates has been developed. The intramolecular allylboration step is very slow in DMSO, which is the usual solvent for these borylations of allylic acetates (see Eq. 33). The use of a non-coordinating solvent like toluene is more suitable for the overall process provided that an arsine or phosphine ligand is added to stabilize the active Pd(0) species during the borylation reaction. With cyclic ketones such as 136, the intramolecular allylation provides cis-fused bicyclic products in agreement with the involvement of the usual chairlike transition structure, 137 (Eq. 102). 

Plumet et al. described domino metathesis of propargyl (2-endo-7-oxanorborn-5-enyl) ethers 62a-62c with allyl acetate in the presence of Grubbs ruthenium catalyst Ic (Scheme 22). The reaction proceeds stereoselectively to produce substituted m-fused bicyclic ethers 63a-63c. In a similar manner, indolizidinone derivative 64 is obtained from compound 62d instead of pyrrolizidine derivative 63d. ... 

Palladium-catalyzed nucleophilic substitutions of activated allylic alcohols have been investigated using a bicyclic phosphine as the chiral element. Reactions have been reported with racemic acyclic allylic acetates <1999TL7791> and cycloalkenyl carbonates <2001TL1297> using the phosphine 203, with good to excellent enantiomeric excesses. 

The rearrangement is also useful for furan aimulation, through enlargement of the starting carbocycle [82]. Thus addition of SnCU to either diastereomer of the allylic acetal produces the cw-fused cycloheptatetrahydrofuran in 48-76 % yield (Eq. 49). Acetals derived from frara-diols rearrange to the same cis-fused bicyclics in higher yield. 

This method was utilized in the preparation of bicyclic compounds consisting of five-, six-, and seven-manbered rings. Oxidative addition of allylic acetates to palladium(O) takes place with inversion of configuration and intramolecular alkene insertion into the... 

Couplings WS Allyl Intermediates- Excellent reviews cover selectivities and mechanism in palladium catalysed allyl reactions. General examples of NaCH(CX)2R)2 additions to allyl acetates, carbonates, and chlorides have appeared. Trifluotoacetale is the preferred leaving group for retention of (E)/( stereochemistry in the case of substituted allyls. Ketomalonates are susceptible to diallylation under PdL2 catalysis especially in the presence of diacetates whidi prove effective routes to bicyclic systems (Equation 6). ... 

When 2-C-benzyl ascorbic acid (50) was acetylated, the open-chain enone (51) was formed, together with the bicyclic triacetate. good route to 2-C-allyl (and hence by reduction, C-alkyl) derivatives of ascorbic acid such as (52) involves the interaction of ascorbate with an allylic acetate or carbonate in the presence of a Pd(0) catalyst. ... 

The enyne metathesis sequence could also be coupled with a subsequent crossmetathesis. As a demonstration of this, Plumet and coworkers exposed 235 to the first generation Grubbs catalyst and allyl acetate to give bicyclic substrate 236 in good yield (Scheme 63). 

Asymmetric 1,3-dipolar cycloadditions of azomethine imines with terminal alkynes have been catalysed by 11 chiral ligand (8) coordinated metal amides to form N,N-bicyclic pyrazolidinone derivatives. Mechanistic studies have established the factors that determine the regioselectivity of the stepwise reaction. Novel phosphoramidite ligands (9) coordinated with palladium have been used to effect enantioselective synthesis of pyrrolidines by 3-P 2-cycloaddition of trimethylenemethane (from 2-trimethylsilylmethyl allyl acetate) to a wide range of imine acceptors (Scheme 11). ... 

The cyclized analog of meralluride is prepared by a similar synthesis. Thus, condensation of camphoric acid (42) (obtained by oxidation of camphor) with ammonia gives the bicyclic succinimide (44). Reaction with allyl isocyanate followed by ring opening and then reaction with mercuric acetate affords the mercury derivative (45) as the acetate rather than the hydroxide as above. Reaction with sodium chloride converts that acetate to the halide (46). Displacement on mercury with the disodium salt of thioglycollic acid affords the diuretic mercaptomerine (47). ... 

Birch reduction-alkylation of 5 with 2-bromoethyl acetate was carried out with complete facial selectivity to give 57. This tetrafunctional intermediate was converted to the bicyclic iodolactone 58 ( > 99% ee) from which the radical cyclization substrate 59 was prepared. The key radical cyclization occurred with complete regio- and facial-selectivity and subsequent stereoselective reduction of the resulting tertiary radical gave 60 with the required trans BC ring fusion.The allylic alcohol rmit of (+)-lycorine was obtained by a photochemical radical decarboxylation, 62 63. 

Fused cyclic ethers can be derived from appropriately substituted sugars. An example is given with the stereoselective 5-exo radical cyclization of allylic 2-bromo-2-deoxysugars, in the presence of 1,1,2,2-tetraphenyldisilane as the radical mediator and AIBN in refluxing ethyl acetate. The corresponding cis-fused bicyclic sugars have been prepared in moderate to good yields (Reaction 7.28) [39]. 

In conjunction with this, Jeong reported the cycloadditions of bis(allyl) and bis(homoallyl) acetals of alkynals leading to bicyclic lactols. Smaltz extended its utility to the synthesis of carbocyclic nucleoside by coupling with nucleophilic substitution of a 7r-allylic palladium complex (Equation (46)). ... 

This subject has recently been reviewed.647 Several additional papers have appeared on the catalytic oxidation of alkenes by 02 in the presence of PdCl(MeCN)2N02(148).64S Terminal alkenes and trans- cyclooctene yield the corresponding ketones, cyclopentene and cyclohexene the corresponding allyl alcohol, and bicyclic alkenes the corresponding epoxide. Heterometallacy-clopentanes such as (152) have been isolated from the reaction of (148) with norbornene (dicy-clopentadiene), and characterized by X-ray crystallography.6486 Glycol monoacetates were obtained from the reaction of (148) with terminal alkenes in acetic acid.649... 

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