Morita-Baylis-Hillman acetates

Moreover, a twofold SN -type domino reaction was reported by Krische and coworkers for the synthesis of y-butenolides 2-229 (Scheme 2.53) [128]. Treatment of Morita-Baylis-Hillman acetates 2-226 with trimethylsilyloxyfuran (2-227) in the presence of triphenylphosphane in THF at 0 °C led to 2-229 in yields of up to 94% and diastereoselectivities of >95 5. 

As shown in Equation (17), 2-trimethylsilyloxyfuran also participated in a triphenylphosphine-catalyzed substitution reaction with Morita-Baylis-Hillman acetates to provide interesting 7-butenolides regio- and diastereoselec-tively <2004AGE6689>. However, the reaction mechanism (vinylogous Michael vs. Diels-Alder) has not been distinguished. 

A twofold Sjj type domino organocatalytic reaction for the synthesis of y-butenolides 28 has been reported by Krische and coworkers [19], by treatment of Morita- Baylis- Hillman acetates 26 with trimethylsilyloxyfuran (27) in the presence of triphenylphosphine to afford 28 in yields up to 94% and diastereoselectivities of >95 5 dr (Scheme 4.6). 

In 2004, Krische and colleagues demonstrated that exposure of Morita-Baylis-Hillman acetates to tertiary phosphine catalysts in the presence of 4,5-dichlorophthalimide enabled regiospecific allylic substitution through a tandem Sn2 -Sn2 mechanism. Through the use of the chiral phosphine catalyst, (i )-Cl-MeO-BIPHEP, the racemic Morita-Baylis-Hillman acetate depicted in Scheme 2.108 was converted into the corresponding enantiomerically enriched allylic amination product, thus establishing the feasibility of DKR. 

Scheme 2.108 DKR of Morita Baylis Hillman acetate catalysed by (R)-Cl-MeO-BIPHEP.

The reaction of several Morita-Baylis-Hillman acetates of 2-azidobenzaldehydes with triethyl phosphite has been described. The products are the 1-diethylphos-phono-l,2-dihydroquinolines (49) and/or the 3-acetoxymethylquinolines (50). The 2 1 1 addition of arysulfonylisocyanates, dialkyl acetylendicarboxylates and dialkyl trialkylsilylphosphites affords the hydantoins (51) as a diastereomeric mixture in excellent yields. ... 

In the course of developing an easy access to chiral y-butenolides, Shi et al. have established an efficient multifunctional chiral binaphthyl phosphine-catalysed allylic substitution of Morita-Baylis-Hillman acetate with 2-tri-methylsiloxy furan. The regjospecific allylic substitution occurred to provide the xyra-y-butenolide in good to excellent yield, high regjoselectivity and excellent enantioselectivity by using water as an additive. The scope of this reaction could be successfully extended to a variety of Morita Baylis Hillman acetates, as shown in Scheme 5.10. 

The introduction of the activated allylic bromides and Morita-Baylis-Hillman acetates and carbonates pioneered the development of a number of phosphine-catalyzed reactions in subsequent years [45]. Interestingly, the asymmetric variant of this type of transformation only appeared in the literature seven years later. In 2010, Tang, Zhou, and coworkers disclosed a highly enantioselective intramolecular ylide [3-f2] annulation using spirobiindane-based phosphine catalyst 31 (Scheme 20.27). BINAP was found inactive in this reaction even at an elevated temperature (70°C). Notably, both optically active benzobicyclo[4.3.0] compounds 32 and 32 with three continuous stereogenic centers could be obtained as major products in high yields and stereoselectivities just by a choice of an additive [Ti(OPr )4], which can block the isomerization of the double bond [46]. 

A new route to 6-substituted pyrrolo[2,l-b]thiazoles 58 takes advantage of an intramolecular thermal cyclization of acetates 56 <07S3037>. These acetates are easily derived from the Morita-Baylis-Hillman adducts of thiazole-2-carboxaldehyde. This strategy has also been extended to the synthesis of the tricyclic analogs 60. 

Shi et al7 reported a highly enantioselective allylic substitution of Morita-Baylis-Hillman (MBH) acetate with TMSOF that could be achieved by chiral prolinamide phosphane organocatalysts 43 in good yield and high ee. 

Acetates of Morita-Baylis-Hillman (MBH) adduct 2 can be stereoselectively prepared by the reaction of acetyl chloride in the presence of a base or, alternatively, acetic anhydride in cone. H2S04. However, acetates 2 derived from aromatic aldehydes (R = Ar) prefer to undergo isomerization to generate the thermodynamically more stable acetate 3, either by intramolecular rearrangement... 

The phosphine (127)-catalysed asymmetric 4 +1-cycloaddition reaction of Morita-Baylis-Hillman carbonates with dicyano-2-methylenebut-3-enoates formed highly functionalized cyclopentenes in high yields and excellent ee% The [RuCl(CO)2]2-catalysed 4 + 1-cycloaddition reaction of alkenyl propargyl acetates, RCH(OAc)C=CC(Me)=CH2, with CO in CH2CI2 produced highly functionalized cyclopentenones in high yields (96%). The chiral copper/Tol-BINAP complex... 

Heteroatom Wittig chemistry also includes reactions of N-sulfonyl imines. It was demostrated that these compounds underwent olefination reactions with nonstabilized phosphonium ylides under mild conditions to afford an array of both Z- and E-isomers of 1,2-disubstituted alkenes, allylic alcohols, and allylic amines.Additionally, studies of the reactions of 5-bromo-4,6-dimethyl-2-thioxo-l,2-dihydropyridine-3-carboni-trile and thiazolidinone with phosphorus ylides have proved the formation of new phosphonium ylides. Annulations via P-ylides are a common occurrence in the literature. For example, on photochemical irradiation, phosphonium-iodonium ylides were shown to undergo 1,3-dipolar cycloaddition reactions with triple bonds, via a carbene intermediate, to yield furans. " Even more common are the reactions of Morita-Baylis-Hillman (MBH) acetates and carbonates. Zhou et al. demostrated that these substrates were able to generate very reactive 1,3-dipoles in the presence of tertiary phosphines the dipoles then underwent cycloaddition reactions to yield annulation products (Scheme 16). ... 

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