Claisen ester rearrangement

A salient structural feature of intermediate 18 (Scheme 2b), the retrosynthetic precursor of aldehyde 13, is its y,r5-unsaturated ester moiety. As it turns out, the Johnson ortho ester variant of the Clai-sen rearrangement is an excellent method for the synthesis of y,<5-unsaturated esters.11 In fact, the Claisen rearrangement, its many variants included, is particularly valuable in organic synthesis as a method for the stereocontrolled construction of trans di- and tri-substituted carbon-carbon double bonds.12,13 Thus, it is conceivable that intermediate 18 could be fashioned in one step from allylic alcohol 20 through a Johnson ortho ester Claisen rearrangement. In... 

A prominent structural feature of 21 and its precursor 22 is the trans C16-C17 trisubstituted double bond. The particular relationship between the ethoxycarbonyl function and the A16 17 double bond in 22 is significant because it satisfies the structural prerequisite for the Johnson ortho ester Claisen rearrangement transform.2130 Mixed ketene acetal 23 thus emerges as the immediate... 

P-citronellene 605 f 612 (/Q-citronellic acid 232, 235 (/ )-citronellol 360 Claisen rearrangement 17, 87, 90, 137 f., 140, 142, 194 -, Johnson ortho ester variant see Johnson ortho ester Claisen rearrangement cobalt-mediated cyclization... 

The ester-Claisen rearrangement procedure of Johnson and coworkers1 2 3 was modified for use with cholest-4-en-3/5-ol. 

CYCLOHEXEN-l-ONE. Importantly, only 1.6 equivalents of Ag20 are required for efficient coupling. The final preparation in this series illustrates the hydrosilation of racemic 3-butyn-2-ol catalyzed by a phosphine based platinum(O) catalyst. The resultant racemic (E)-vinylsilane is then resolved with a commercially available lipase and subjected to a Johnson ortho ester Claisen rearrangement to afford [3R- AND 3S-]-(4E)-METHYL... 

The three-step procedure described for the preparation of the illustrated crotylsilanes is initiated with the hydrosilation of rac-3-butyn-2-ol. This procedure is significantly improved with respect to the positional selectivity of the hydrosilation resulting in exclusive formation of the racemic (E)-vinylsilane, and as a result the present procedure is much more amenable to scale-up than those previously described in the literature.8 The enzymatic resolution of the racemic secondary allylic alcohol (vinylsilane) has also been reported using commercially available lipase extracts. The use of a Johnson ortho ester Claisen rearrangement affords the (E)-crotylsilanes 4 in nearly enantiomerically pure form. 

The mechanism and stereochemistry of the ortho ester Claisen rearrangement are analogous to those of the Cope rearrangement. The reaction is stereospecific with respect to the double bond present in the initial allylic alcohol. In acyclic molecules, the stereochemistry of the product can usually be predicted on the basis of a chairlike transition state.158 When steric effects or ring geometry preclude a chairlike structure, the reaction can proceed through a boatlike transition state.159... 

A reaction which is related to the ortho ester Claisen rearrangement utilizes an amide acetal, such as dimethylacetamide dimethyl acetal, rather than an ortho ester in the exchange reaction with allylic alcohols.174 The stereochemistry of the reaction is analogous to that of the other variants of the Claisen rearrangement.175... 

The ester Claisen rearrangement that converts optically active allyl alcohol (2 )-2-methyl-1-penten-3-ol into the a-substituted carboxylic acid 4 (for assignment, see p 452)144,145. 

K. Tadano, Y. Idogaki, H. Yamada, and T. Suima, ortho Ester Claisen rearrangements of three... 

The Johnson Claisen rearrangement,31 also called the ortho ester Claisen rearrangement, involves the reaction of an allylic alcohol with an ortho ester, often triethyl orthoacetate, in the presence of a carboxylic acid such as propionic acid, usually at temperatures between 120 and 140 JC (Scheme 3).1 The intermediate kctcnc acetal rearranges stereoselectively. 

Ortho ester Claisen rearrangement.2 The [3,3]sigmatropic rearrangement of allyl vinyl alcohols prepared from this ester results in a regiospecific synthesis of diethyl allylmalonates. 

The Carroll rearrangement, a variation on the ester Claisen rearrangement, is a useful method for the preparation of y, 8-unsaturated ketones from allyl acetoacetates, and has been adapted to provide a method for the synthesis of a number of specific arylacetones. Thus, treatment of the p-quinol 1 with diketene and a catalytic amount of DMAP at room temperature gave a 72% yield of the arylacetone 2 together with 5% of the benzofuran 3. 

Siikrishna, A. and Nagaraju, S. 1992. Acceleration of ortho ester Claisen rearrangement by a commercial microwave oven. Journal of Chemical Society, Perkin Transactions, 1 311-12. 

In the acid-catalyzed ortho ester Claisen rearrangement of allylic alcohol (303) with trimethyl orthobutyrate, diastereomers (304), (305) and (306) were isolated in a ratio of 63 30 7 (Scheme 53). The 3,3-sigmatropic rearrangement occuned with a high degree of stereofacial selectivity from the p-face of the allylic alcohol (a >13 1 for Ht). In contrast, Qaisen rearrangement of the enol ether (307) at 135-140 C (PhH, sealed tube) provid the desired -dicarbonyl compound (308) as a single diastereomer at... 

The a-substituted 1-methyl allyl vinyl ether was shown to isomerize with a strong preference for the irons product (i.e., 95 % irons, 5 % cfe) . This corresponds to a conformational preference for equatorial methyl (as opposed to axial) in the chair transition state of about 2.4 kcal.mole . The identical value was calculated from the irons product preference in the allyl ester Claisen rearrangements (see a-methyl allyl acetate and a-trifluoromethyl allyl trifluoroacetate). 

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