Imines with allyl silanes

The development of new methods for the synthesis of homoallylic amine derivatives is an important area of synthetic efforts. Homoallylic amines are extremely important compounds as biologically active molecules [1], The Lewis acid-mediated reactions of imines with allyl silanes are among the most efficient for... 

Table 1 Reactions of in situ Generated N-Tosyl Imines with Allyl Silanes...

Synthesis of homoallylamines by catalytic asymmetric allylation of imines with allyl silanes using a chiral bis x-allyl palladium complex, also using allylstannanes (see 1st edition). 

Scheme 5.2 Allylation to imine with allylic silane 5.

Oxazolidine 144 obtained from amino alcohol 143 and ethyl trifluoropyruvate is also a synthetic intermediate for 2-amino-2-trifluoromethylpentanoic acid 145. Lewis acid-catalyzed allylation of 144 with allyl silane occurs in excellent yield with a moderate stereoselectivity. Meanwhile, O-tert-butyldimethylsilyl-protected imine 146 gives better diastereoselectivity although yield is poor (see Scheme 9.31) [57]. 

A few other studies of allylations of N-sulfonyl imines by allylic silanes have been published. Shono et al. found that azetidine derivative 22 can be converted to allyl compound 115 [25b] [Eq. (26)]. The functionalized sulfonamides 116 [Eq. (27)] have all been alkylated with allyl trimethylsilane and Lewis acids [34]. In general, the best yields of 117 were obtained with SnCl4, BF3 etherate, Znl2 and FeCl3 as catalysts. Lower yields were obtained with TiCl4 and Et2AlCl. Similarly, the a-hydroxy and a-methoxy sulfonamides 51 could be alkylated to give... 

Activation by silicon of a P-C-H bond to an intramolecular carbene insertion reaction is exemplified by the silicon-directed Bamford-Stevens reaction.68 For example, thermal decomposition of P-trimethylsilyl /V-aziridinyl imines 72 in toluene (Scheme 8) [with or without Rh2(OAc)4 catalyst] results in the formation of allylic silanes 73 as major or exclusive products by the preferential insertion of the carbene intermediate into the C-H bond P to the silicon substituent. 

Allylic silanes were also good reagents for Pd-catalyzed allylation reactions. The alkylation of imines has been achieved in the presence of 1 and TBAF as cocatalyst system (eq 39). This reaction was compatible with various imines and was smoothly applied to aldehydes. 

This book chapter is limited to Lewis acid-mediated reactions, and does not discuss the important field of Lewis base-mediated allylations, nor does it describe the reactions of allylsilanes with other electrophiles such as epoxides, imines, and allyl-X (X = -Cl, -OR, -OAc). The SaJcurai reaction has been covered under different forms in reviews focusing on The Stereochemistry of the Sakurai reaction , Intramolecular Addition Reactions of Allylic and Propargylic Silanes ," Selective Reactions Using Allylic Metals , Catalytic Enantioselective Addition of Allylic Organometallic Reagents to Aldehydes and Ketones , and Modem Carbonyl Chemistry . ... 

In the past, aldehydes have been efficiently a-alkylated using two-electron chemistry. David W. C. Macmillan of Princeton University has developed (Science 2007, 316, 582 J. Am. Chem. Soc. 2007, 129, 7004) a one-electron alternative. The organocatalyst 9 formed an imine with the aldehyde. Qne-electron oxidation led to an a-radical, which was trapped by the allyl silane (or, not pictured, a sdyl enol ether) leading to the a-alkylated... 

The chiral Bronsted acids (249-250) have been shown to initiate the Hosomi-Sakurai reaction of imines (246) with allyl- and crotyltrimethyl-silane (247) to give products (248) with excellent enantioselectivities (Scheme 64). ... 

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