Cycloaddition reactions chiral cyclobutanones

Cycloaddition Reactions. Chiral acrylamides derived from pyrrolidines (2) or (3) undergo stereoselective [4 + 2] cycloaddition reactions with a variety of cyclic dienes. Similarly, nitroso compounds derivatized with pyrrolidine (2) and generated in situ give cycloadducts with a high degree of stereoselectivity (eq 6). Intramolecular [2 + 2] cycloadditions involving pyrrolidine-derived keteniminium salts have been shown to produce chiral cyclobutanones. ... 

Since 1,3-disubstituted allcnes can exist in two enantiomeric forms, the use of partially resolved allenes in these cycloadditions led to some early reports of chiral cyclobutanones. For example, reaction of dimethylketene with partially resolved (/ )-l,3-dimethylallene (4, R = Me) or (/ )-1.3-di-/er -butylallcnc (4, R = r-Bu) gave the corresponding 2-alkylidenecyclobutanones 5 and 6 with the R configuration at the newly created stereogenic center.3... 

The use of alkenes with chiral auxiliary groups leads to chiral cyclobutanones 4. Reaction yields of 50 67% and diastereomeric excesses of 86-97% were obtained for the 3-amidocy-clobutanones which were obtained from cycloaddition of the chromium carbene complexes with chiral ene carbamates (see also Section 1.3.4.3.3.).11... 

No reaction occurs with vinyl ethers, silyl enol ethers, or ketene silyl acetals, usually used in thermal [2 + 2]cycloaddition reactions, but the present case is the first example of the preparation of a chiral cyclobutanone by a cycloaddition route. 

The chiral titanium reagent (6) also catalyzes the [2 + 2] cycloaddition reaction of 1,3-oxazolidin-2-one derivatives of a,(3-unsaturated carboxylic acids and ketene dithioacetals in the presence of MS 4A to give cyclobutanone dithioacetal derivatives with high optical purity (eq 10). Vinyl sulfides, alkynyl sulfides, and 1,2-propadienyl sulfides can also be employed in this reaction to give the corresponding cyclobutanes, cyclobutenes and methylenecyclobutane derivatives with high optical purity (eqs 11 and 12). ... 

The 2 -I- 2-cycloaddition reactions of chiral Al-alkynylated sulfoximines with ketenes afforded sulfoximine-functionalized cyclobutenes in high yields. The first examples of Lewis-acid-promoted ketene-alkene 2-i-2-cycloadditions yielded cyclobutanone cycloadducts with good yields and diastereoselectivity. " ... 

In an extension of previous work, it has been found that Pd(0)-catalysed intramolecular cyclization of allylic acetates (21) can be used to prepare the chrysanthemic acid analogues (22). The potentially useful cw-cyclopropane (23) can be simply obtained by base-induced addition of cyanoacetate to ethyl 2-bromo-3,3-dimethylacrylate followed by decarboxylation oddly, a similar reaction using malonate fails to give a cyclopropane. Optically pure dichloro cw-chrysanthemic acid (26) has been obtained by a Favorskii rearrangement of the chiral cyclobutanone (25) prepared from the keten (24) by sequential [2 + 2]cycloaddition, cine-rearrangement, and resolution (Scheme 3). ... 

Various chiral cyclobutanone derivatives have been prepared by cycloaddition of dichloroketene to the glycal (1), as shown in Scheme 1. A number of other reactions of (2) and (3) were also reported, including Baeyer-Villiger oxidations to y-lactones.. S... 

An ab initio study of the 2 + 2-cycloadditions of allene to isocyanic acid and ketene to vinylimine found the reactions to be concerted and mostly asynchronous.28,29 The diastereoselective 2 + 2-cycloaddition of dichloroketene with a chiral enol ether (26) produced the cyclobutanone (27), which leads to a key intermediate (28) in (g) the total synthesis of the natural alkaloid (-)-Swainsonine (29) (Scheme 8).30 The... 

Irradiation of alkoxycarbene complexes in the presence of aUcenes and carbon monoxide produces cyclobutanones. A variety of inter- and intramolecular [2 + 2]cycloadditions have been reported. The regioselectivity is comparable with those obtained in reactions of ketenes generated from carboxylic acid derivatives. Cyclobutanones can be obtained with a high degree of diastereoselectivity upon reaction of alkoxy carbenes with chiral A-vinyloxazolidinones. For example, photolysis of (19) in the presence of (20) gives cyclobutanone (21) (Scheme 31). In addition to aUcoxycarbenes, carbenes having a thioether or pyrrole substituent can also be employed. Related intramolecular cycloadditions of y,5-unsaturated chromimn carbenes afford bicyclo[2.1. IJhexanones (Scheme 32). 

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