Dimethylhydrazones,

A. 0-Methyl-ls -2-octalone id,lA-Dimethylhydra2one. A 250-ml., round-bottomed flask equipped with a magnetic stirring bar and a Dean-Stark water separator is maintained under a dry nitrogen atmosphere (Note 1) and eharged with 7.4 g. (0.045 mole) of 10-methyl-A -2-oetalone [2(3 f)-Naphthalenone, 4,4a,5,6,7,8-hexahydro-4a-methyl-] (Note 2), 9.0 g. (0.15 mole) of N,N-dimethylhydrazine, 150 ml. of dry benzene, and 0.02 g. of p-toluenesulfonie aeid. This mixture is refluxed for 10-14 hours, after whieh time no further water separates. Benzene and excess N,A -dimethylhydrazine are then removed by simple distillation, and the residue is distilled under reduced pressure to give 8.1 g. (87%) of the dimethylhydrazone as a pale-yellow liquid, b.p. 94-98 (0.2 mm.) (Notes 3, 4). 

Iodine fluoride is a more versatile reagent than molecular fluorine in geminal fluorination of other hydrazones and related compounds under milder reaction conditions [55] Substrates fluorinated include hydrazones of simple cyclic or steroidal ketones (e g, 4 tert butylcyclohexanone, 70%, 3 cholestanone, 70%), W methyl and A/N dimethylhydrazones [R2C=NNH(CH3) 70%, R2C=NNC(CH3)2, 50%], semicarbazones (R2C=NNHCONH2, 25-50%), and 2,4-dinitrophenylhy-drazones [R2C==NNH-C6H3-2,4(N02)2, 25-50%]... 

Modem technology has influenced these reactions. Ultrasound assisted versions of these reactions has been reported. Ultrasound irradiation facilitated the Diels-Alder reaction of dimethylhydrazone 94 with 95. The resultant pyridine 96 are afforded in shorter reaction times and increased yields. 

Scheme 5 details the asymmetric synthesis of dimethylhydrazone 14. The synthesis of this fragment commences with an Evans asymmetric aldol condensation between the boron enolate derived from 21 and trans-2-pentenal (20). Syn aldol adduct 29 is obtained in diastereomerically pure form through a process which defines both the relative and absolute stereochemistry of the newly generated stereogenic centers at carbons 29 and 30 (92 % yield). After reductive removal of the chiral auxiliary, selective silylation of the primary alcohol furnishes 30 in 71 % overall yield. The method employed to achieve the reduction of the C-28 carbonyl is interesting and worthy of comment. The reaction between tri-n-butylbor-... 

Substituted 3-Hydroxyalkanal Dimethylhydrazones 2 General Procedure for Aldol-Type Addition of Ti-tanated Dimethylhydrazones2 ... 

In the case of titanated cyclohexanone dimethylhydrazone 3 the. wt-adduct is obtained nearly... 

Metalation ofa-sulfinyl dimethylhydrazones with terf-butylmagnesium bromide, butyllithium or lithium diisopropylamide, and reaction of the generated azaenolates with aldehydes, provides aldol adducts (e.g., 6) as mixtures of diastereomers. Reductive desulfurization leads to fi-hydroxy dimethylhydrazones (e.g., 7) which are cleaved to the desired /(-hydroxy ketones in 25% overall yield10 u. The enantiomeric excesses are about 50%, except for (- )-3-hydroxy-4-methyl-1-phenyl-1-pentanone (8) which was obtained in 88% ee. 

Addition of metalated, enantiomerically pure a-sulfinyl dimethylhydrazones (e.g., 9) to racemic a-chiral aldehydes 10 proceeds with good to excellent diastereo- and enantioselectivi-ty12. Diastereomeric ratios increase with increasing steric demand of the acetaldehyde substituent R1 compared to the methyl group, and each diastereomer is obtained with high enantiomeric excess. In the aldol-lype addition to 2-phenylpropanal, one of the four possible stereoisomers is formed selectively. The relative (syn) and absolute (R.R) configuration is in accord with Cram s and related rules as well as H-NMR data of closely related compounds. 

To a stirred solution of 2.0 mmol of the a-[(/ )-4-methylphenylsulfinyl] dimethylhydrazone (e.g., 9) in 50 mL of THF at —90 °C, 3.0 mmol of BuLi in hexane are added, followed, after 30 min, by 1 mL (6 mmol) of HMPA. After a further 30 min of stirring, 6.0 mmol of the aldehyde are added and the mixture is stirred for 3 h at — 90 C. The reaction mixture is hydrolyzed with sat. aq NH4C1 and the aqueous layer extracted with three 40-mL portions of Ei20. The organic layers are combined, dried over Na2S04, and evaporated under reduced pressure to give the adducts which are used as such for the subsequent reaction. 

Enolates derived from various imino compounds have been sulfinylated in reactions analogous to those shown by equations (14) and (15). Some representative examples are shown in equations 16-18. Here again, these compounds have been utilized in asymmetric syntheses. Addition of sulfinate ester 19 to a THF suspension of a-lithio-N,N-dimethylhydrazones, derived from readily available hydrazones of aldehydes and ketones, leads to a-sulfinylhydrazones in good yield, e.g. 53 and 54 (equations 16 and 17)85,86. Compounds 53 and 54 were obtained in a 95/5 and 75/25 E/Z ratio, respectively. The epimer ratio of compound 53 was 55/45. Five other examples were reported with various E/Z and epimeric ratios. 

Fischer alkenylcarbene complexes undergo cyclopentannulation to alkenyl AT,AT-dimethylhydrazones (1-amino-1-azadienes) to furnish [3C+2S] substituted cyclopentenes in a regio- and diastereoselective way along with minor amounts of [4S+1C] pyrrole derivatives. Enantiopure carbene complexes derived from (-)-8-(2-naphthyl)menthol afford mixtures of trans,trans-cycloipentenes and ds,ds-cyclopentenes with excellent face selectivity [75]. The mechanism proposed for the formation of these cyclopentene derivatives is outlined in Scheme 28. The process is initiated by nucleophilic 1,2-attack of the carbon... 

The reaction of JV,iV-dimethylhydrazones (1-amino-1-azadienes) and alkenylcarbene complexes mainly produces [3C+2S] cyclopentene derivatives (see Sect. 2.6.4.5). However, a minor product in this reaction is a pyrrole derivative which can be considered as derived from a [4S+1C] cycloaddition process [75]. In this case, the reaction is initiated by the nucleophilic 1,2-addition of the nitrogen lone pair to the metal-carbon double bond followed by cyclisation and... 

Both sides of acetone have been alkylated with different alkyl groups, in one operation, by treatment of the Al,lV-dimethylhydrazone of acetone with n-BuLi, followed by a primary alkyl, benzylic, or allylic bromide or iodide then another mole of n-BuLi, a second halide, and finally hydrolysis of the hydrazone. ... 

The iV,A -dimethylhydrazone is prepared first and then treated with hydrazine ... 

This is known as the directed aldol reaction. Similar reactions have been performed with oc-lithiated dimethylhydrazones of aldehydes or ketones and with a-lithiated... 

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