Formals, dialkyl synthesis

In an innovative extension of the chemistry of chiral bicyclic lactams, Meyers disclosed that dialkylated lactam 98 could be reduced with Red-Al and hydrolyzed to the corresponding ketoaldehyde 100, which underwent aldol condensation to give cyclohexenone 101 (>95% ee. Scheme 3.16) [75, 76]. The product subsequently served as a key intermediate in a formal total synthesis of aspidospermine (102) [75]. These chiral bicyclic lactams developed by Meyers can generally be relied upon for the preparation of a variety of chiral building blocks including cyclopropanes, cyclopentenones, and cyclohexenones (see insert on the left) [68, 69]. 

A high yield synthesis involving formal oxidation of a sulphoxide to a sulphoximine has been reported183 using O-mesitylenesulphonyl hydroxylamine (NH2OMes) (equation 67). The reaction is successful for a wide range of sulphoxides including dialkyl, diaryl and cyclic species. 

Ketenedithioacetals (1) can formally be considered as S.S-dialkylated dithioacids. However, their reactivity pattern is quite different from that displayed by compounds like dithioacids and dithioesters bearing a thiocarbonyl group, and their syntheses and properties are usually treated apart. The review by Kolb [59] and its 254 references give access to most of the literature in the field (see also [60]). a-Oxoketenedithioacetals (2) are particularly versatile compounds as three-carbon synthons in organic synthesis, and some reviews deal specifically with them [61, 62]. Many efficient procedures are available for their syntheses [59, 61], and number of these make use of the reactions of carbon disulfide with carbanionic species followed by alkylation at the sulfur atoms (see [63] and [64] for the reactions of CS2). 

The synthesis of aliphatic polyformals (X) been known for many years and is relatively straightforward. As shown in equation 1, aliphatic diols can be reacted directly with formaldehyde or dialkyl formals to produce these polymers. The principal complication of the reaction occurs when the diol used contains 2, 3 or 4 carbon atoms in which case the formation of the cyclic formal is favored. Musser and Jackson have more... 

Alkyl thiocyanates react with a variety of nucleophiles to yield thioethers (see Sect. 13.4). A particularly clever and useful application of this reaction is the dialkylation of phenylacetonitrile with 1,2-dithiocyanatoethane. The product of this formal oxidation is the ethylenedithioketal of benzoyl cyanide (see Eq. 10.18) [30]. The phase transfer synthesis of the starting material from thiocyanate ion and ethylene bromide... 

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