Lithium hydride acyl halides

The reactions of Meldrum s acid (421) and acyl isothiocyanates in DMSO in the presence of lithium hydride at ambient temperature for 2-3 hr gave the lithium salts (457), which were alkylated by treatment with alkyl halide for 5 hr to afford isopropylidene (acylamino)(alkylthio)methy-lenemalonates (458) in 20-90% yields (87ZC68). 

Acyl halides can be reduced to aldehydes1206 by treatment with lithium tri-f-butoxyaluminum hydride in diglyme at -78°C,1207 R may be alkyl or aryl and may contain many types of substituents, including N02, CN, and EtOOC groups. The reaction stops at the aldehyde stage because steric hindrance prevents further reduction under these conditions. Acyl halides can also be reduced to aldehydes by hydrogenolysis with palladium-on-barium sulfate... 

Acyl halides can be reduced to aldehydesby treatment with lithium tri-tcrt-butoxyaluminum hydride in diglyme at The R group may be alkyl... 

Some reactions of alcohols 104 with isocyanates (93T6849) have been reported, as have reactions of acyl halides with 104 (R = SMe), 105 (93T6849), and 106 (93CC417). In turn, alcohols of type 104 and 105 have been prepared by lithium aluminium hydride reduction of the corresponding ketones or through deprotection of their O-rm-butyldiphenylsilyl derivatives (91TL6033 93T6849). 

There are two commonly used reducing agents, namely first—sodium horohydride (NaBH ) which reduces exclusively aldehydes, ketones and acyl halides and secondly—lithium aluminium hydride (LiAlH ) which reduces the above compounds as well as compormds belonging to the carboxylic acid family. 

The use of acyl azides in the preparation of amines by the Curtius rearrangement has been discussed previously (Section 23-12E). Alkyl azides can be reduced readily by lithium aluminum hydride to amines and, if a pure primary amine is desired, the sequence halide — azide — amine may give as good or better results than does the Gabriel synthesis (Section 23-9D). 

Alkyl and acyl derivatives (28, 30) of 14-aminocodeinones (13, 26) and dihydro-codeinones (20a, 27) are readily prepared acylation is achieved under standard conditions of acid chloride or acid anhydride in the presence of an organic base, while alkylation can be achieved directly with an alkyl halide or by acylation and then lithium aluminium hydride reduction (Scheme 5). In this latter method the 6-keto group is protected as an acetal [8, 9, 18, 19]. For direct alkylation with unactivated alkyl halides, carrying out the reaction in a sealed tube at 120 °C has... 

Sodium/ammonia" treatment also causes disruption of the ring in thiophene and simple thiophenes, however thiophene-2-carboxylic acid and 2-acyl-thiophenes can be converted into the 2,5-dihydro derivatives using lithium in ammonia, followed by protonation or trapping with an alkyl halide."" Side-chain reductions can be carried out with metal hydrides, which do not affect the ring. 

Acyloins (la) [29,30] and bis-silylated derivatives of their enediols (lb) [31] have been demonstrated to be useful acyl anion equivalents (RCO ) and have been employed in an indirect but facile way for the preparation of ketones (3) (Equation 7.1). The hydroxy ketones (2), which are the key intermediates in this method, have been prepared by the reaction of acyloins (la) with organic halides in the presence of sodium hydroxide in dimethyl sulfoxide [29, 30] according to the Hein s procedure [32] or using sodium hydride in 1,2-dimethoxyethane (DME) (glyme) [33]. They also have been prepared by the alkylation of lithium enedi-olates of acyloins prepared from the corresponding lb and methyllithium [31]. These reactions proceed with C-alkylation however, the reaction conditions employed are quite basic which would limit substrate choice. 

---