Allyl carbonates 2.3.3- trisubstituted

Type III (no homodimerization) Acrylonitrile," protected 3° allylamines" Vinyl trialkoxysilanes, vinyl siloxanes 1,1-Disubstituted olefins, " non-bulky trisubstituted olefms, vinyl phosphonates, " vinyl phosphine oxides,phenyl vinyl sulfone, acrylonitrile, 4° allylic carbons (all alkyl substituents), protected 3° allylic alcohols, 7,Aolefm of 2-subst. 1.3- butadienes, 7,Aolefin of electronically deactivated 1.3- butadienes ... 

Type IV (spectators to CM) 1,1-Disubstituted olefms " 1,1-Disubstituted olefms, disub. o ,/ -unsaturated carbonyls, 4° allylic carbon-containing olefins, perfluorinated alkane olefins, 3° allylamines (protected)" Vinyl nitro olefins, protected trisubstituted allyl alcohols, a,/ -olefin of 2-subst. 1.3- butadienes, a,/ -olefm of electronically deactivated 1.3- butadienes ... 

Extension of the above oxidation studies to alkenes such as limonene gave a complex mixture of products that resulted from all possible ene reactions to the trisubstituted double bond (Fig. 30) [165], However, use of NaY zeolite as the microreactor and in the presence of a small amount of pyridine, the photosensitized oxidation of the alkenes is regioselective, yielding only the cis and trans products that result from hydrogen abstraction from the least hindered allylic carbon center. These studies illustrated that a microreactor can provide unprecedented opportunities to conduct selective oxidation of olefins. 

Rhodium(ll)-catalyzed etherification of an allylic carbonate with enantiopure alkenyl alcohols 246 followed by RCM proceeds with excellent diastereoselectivity to afford syn-247 or /f-3,6-dihydropyrans 248 in high yield (Scheme 68) <2004AGE4788>. This methodology can be extended to the preparation of chiral 2,3,6-trisubstituted 3,6-dihydropyrans <2004JA8642>. 

Fully substituted triazoles were synthesized via the four-component coupling reaction of the unactivated silylacetylenes 50, two equivalents of allyl carbonates 5b, and trimethylsilyl azide 42 in the presence of a Pd(0)-Cu(I) bimetallic catalyst (Scheme 18) [54], Various trisubstituted 1,2,3-triazoles were obtained in good yields. The reaction most probably proceeds through the formation of alkynylcopper species 52, which on cross-coupling reaction with the 7r-allylpalladium complex 53 gives the products 51. 

Combined with the efficient and regiospecific alkylation of allylic sulphones shown in the Scheme (contrast the corresponding alkylation of allylic sulphox-ides), this method can give allylic alcohols trisubstituted on the carbon-carbon double bond. The sequence can also be adapted to open up two new routes to exocyclic a-methylene-carbinols (32) (Scheme 15)/" either by overall [1,3] transposition of oxygen from (33), or from ketones via the vinyl sulphones (34), which are isomerized to the thermodynamically favoured allylic isomers (35). 

Miscellaneous Transformations. Cyanotrimethylsilane effects the transformation of acyl chlorides to acyl cyanides, a-chloro ethers and a-chloro thioethers to a-cyano ethers and a-cyano thioethers (eq 19), t-butyl chlorides to nitriles (eqs 20 and 21), 1,3,5-trisubstituted hexahydro-l,3,5-triazines to amino-acetonitriles, the cyanation of allylic carbonates and acetates (eqs 22 and 23), and the formation of aryl thiocyanates from aryl sulfonyl chlorides and sulfinates. The reagent has been used effectively in peptide synthesis and in a range of other synthetic applications. " ... 

Copper(II)-catalyzed Boryl Addition to Allylic Carbonates. The conversion of allylic carbonates to chiral a-substituted allylboronates was also investigated by Hoveyda, who was able to accon ilish this transformation with a Cu(II)-NHC complex. This reaction proceeds in a vinylogous fashion to Sawamura s, but under these conditions, (E)- and (Z)-allylic carbonates undergo substitution to produce opposite enantiomers of product with similar yields and selectivity. This methodology is also tolerant of substitution at the a- or -position and is effective for di-or trisubstituted alkyl (linear or branched) or aryl alkenes delivering a quaternary a-chiral allylboronate product with up to 98% enantioselectivity (eq 49). 

A second C34 isomer (18) was isolated as a major constituent from a Martinique strain originating from a small pool in Paquemar (52) it accounted for 72% of the total hydrocarbon fraction. Structure (18) was proposed on the basis of NMR spectral evidence and ozonolysis degradation leading among other products to the ketoacid (17). The cis configuration of the trisubstituted C(5)-C(6) double bond was based on the chemical shift (534.5) of the allylic carbon C(7) which would be more deshielded in a trans configuration (539-40). 

Allylation of the 10-carborane 236 (pKa = 18-22) with diallyl carbonate is possible under neutral conditions to give 237[146], Allylation and rearrangement of the trialkylalkynylborane 238 affords the trisubstituted alkene 239 stereoselectively [ 147],... 

For trisubstituted olefins, the nucleophile attacks predominantly at the less substituted end of the allyl moiety, e.g. to afford a 78 22 mixture of 13 and 14 (equation 7). Both the oxidative addition of palladium(O) and the subsequent nucleophilic attack occur with inversion of configuration to give the product of net retention7. The synthesis of the sex pheromone 15 of the Monarch butterfly has been accomplished by using bis[bis(l,2-diphenylphosphinoethane)]palladium as a catalyst as outlined in equation 87. A substitution of an allyl sulfone 16 by a stabilized carbon nucleophile, such as an alkynyl or vinyl system, proceeds regioselectively in the presence of a Lewis acid (equation 9)8. The... 

Trisubstituted carbon-centred radicals chemically appear planar as depicted in the TT-type structure 1. However, spectroscopic studies have shown that planarity holds only for methyl, which has a very shallow well for inversion with a planar energy minimum, and for delocalized radical centres like allyl or benzyl. Ethyl, isopropyl, tert-butyl and all the like have double minima for inversion but the barrier is only about 300-500 cal, so that inversion is very fast even at low temperatures. Moreover, carbon-centred radicals with electronegative substituents like alkoxyl or fluorine reinforce the non-planarity, the effect being accumulative for multi-substitutions. This is ascribed to no bonds between n electrons on the heteroatom and the bond to another substituent. The degree of bending is also increased by ring strain like in cyclopropyl and oxiranyl radicals, whereas the disubstituted carbon-centred species like vinyl or acyl are bent a radicals [21]. 

Thus, trisubstituted alkenes are preferentially oxidized at one of the allylic groups at the disubstituted carbon. 

The reaction is 100% stereoselective and affords 69 as a unique stereomer with the (/f)-configuration at C-6, assigned by X-ray analysis. Consequently, the configuration at C-6 results from the well-known chair transition state model for the (Z)-O-allyl enol 68 in which the aUyl unit is on the opposite side to the isopropylidene ketal at C3-C4 and reacts on the Si face of the trisubstituted carbon-carbon double bond. Such a transition state leads to the sole (/ )-configuration in 69. 

Trisubstituted epoxides react to give allylic alcohols in which the hydroxyl group is linked to the less substituted carbon. 

Hoppe, D. Bronneke, A. Highly diastereose-lective synthesis of di- and trisubstituted 4-butanolides from aldehydes and ketones via three-carbon-extension by allylic homoenolate reagents. Tetrahedron Lett. 1983, 24, 1687-1690. 

The two ends of the allylic system are contrasted sterically direct (S>j2) attack is at a primary carbon while allylic (S pO attack is at a tertiary carbon atom so that steric hindrance favours the Sn2 reaction. In addition, the number of substituents on the alkene product means that the S 2 product is nearly always preferred—Sn2 gives a trisubstituted alkene while the S 2 product has a less stable monosubstituted alkene. 

Substituted allylic ethers were transformed predominantly into trans-1,2-di- and -1,1,2-trisubstituted cyclopropanes (Table 6). The degree of trans selectivity depends on the OR group, and is higher with R=Me than with Bn (entries 1 and 2), the diastereoselectivity being generated in the hydro-zirconation step [29]. Furthermore, the cyclization step proceeds with the inversion of the configuration at the carbon atom bound to zirconium [30]. 

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