Organometallic reagents, with cyclic

Like the reaction of organometallic reagents with cyclic sulfites, reaction of 1,2,3-oxathiazolidine 2-oxide 107 derived from ephedrine (106) and thionyl chloride with a Grignard reagent (RMgX) or an alkyllithium (QHsLi or MeLi) furnished a mixture of sulfinamides 110. 

Stereodivergent pathways relative to other allylic systems (e.g. allylic acetates) have been found in the reactions of cyclic allylic sulfides or ethers of benzothiazole with organocopper reagents. In this case the Sn2 process occurs with syn stereochemistry (eq 5) and is due to the anchimeric coordination of the organometallic reagent with the heterocyclic moiety. This has been utilized for regio- and stereocontroUed access to branched-chain sugars. 

Organometallic reagents and alkali metal amides can react via a cyclic transition state (Section II, B, 5) beginning with electrophilic attack at the most basic ring-nitrogen. As a result, sodamide (in dimethylaniline, 145°, 2 hr) yields the 4-amino derivatives (40% yield S)) methyl- or phenyl-magnesium iodides give the 4-adduct quantitatively.s ... 

In his original paper,2 Cram disclosed an alternative model that rationalizes the preferred stereochemical course of nucleophilic additions to chiral carbonyl compounds containing an a heteroatom that is capable of forming a complex with the organometallic reagent. This model, known as the Cram cyclic or Cram chelate model, has been extensively studied by Cram9 and by others,410... 

To make ethers more reactive, they must be complexed with strong Lewis acids. BF3 is commonly used with cyclic ethers, and even with epoxides it increases the rate and yield of the reaction when organometallic reagents are used as nucleophiles. BF3 is most easily handled as its complex with diethyl ether, written BF3 OEt, BuLi does not react with oxetane, for example, unless a Lewis acid, such as BF3, is added, when it opens the fouremembered ring to give a quantitative yield of H-heptanoI. 

Treatment of a thirteen-membered lactam with 1-naphthylmagnesium bromide forms both a cyclic enamine and the amino ketone412. Imides of dicarboxylic acids produce with organometallic reagents cyclic enamino compounds such as 108 (n = 1, 2)413-418. 

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