2- cyclohexanone sulfur ylide

The intermediacy of such oxaspiropentanes has been proposed in the addition of diazomethane to ketonesi0) and in the reaction of dimethyloxosulfonium methylide with a-haloketones55). In contrast to phosphorous ylides, sulfur ylides usually condense with carbonyl compounds to yield epoxides, thus reaction of the N,N-dimethylaminophenyloxosulfonium cyclopropylide 99 with cyclohexanone produced the dispiroepoxide 100 which rearranged to the spiro [3.5] nonan-l-one 101 upon isolation by gas chromatography, Eq. (29) S6). 

The sulfur ylide 3.45 on reaction with cyclohexanone gives oxirane 3.64, while the phosphorus ylide 3.65 gives the alkene 3.66. 

The high nucleophilicity of a-selenoalkyllithiums towards carbonyl conqiounds, even those that are the most hindered or enolizable, such as 2,2,6-trimethyl- and 2,2,6,6-tetramethyl-cyclohexanone (Schemes 113 and 164), di-t-butyl ketone, pennethylcyclobutanone, peimethylcyclopenta-none (Schemes 113 and 187) °- and deoxybenzoin (Schemes 115, 116 and i65y 4 49 23 iqws the synthesis of related alkenes, epoxides and rearranged ketones which are not available from the same carbonyl compounds on reaction with phosphorus or sulfur ylides - or diazoalkanes. ... 

Early efforts to probe the stereochemistry of sulfur ylide additions have been reviewed. Ylide (1) reacts with unhindered cyclohexanone derivatives to give products resulting from axial attack, whereas (2) gives rise to net equatorial addition. This is again due to the tendency of (1) to undergo l etically controlled reactions and (2) to give products resulting from thermodynamic control. However, equator attack may prevail even in kinetically controlled reactions if axial attack is rendered sufficiently hindered, e.g. by 1,3-diaxial interactions or by additional steric bulk adjacent to the reactive caibonyl. For example, the addition of (1) to ketone (9) afibrds the -epoxide shown in equation (6) exclusively. Other cyclic systems react with fairly predictable stereoselectivities in accord with the above observa-... 

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