Retirement plans mostly corral participants into investing in securities and bonds. Real estate investing, particularly investing in syndicated multifamily real estate, is beyond the scope of employer-sponsored 401(k) plans and standard IRAs. However, a self-directed IRA and a solo 401(k) can be set up for real estate investing.  These specialized accounts can unlock multifamily real estate's potential for higher returns. They appeal to people because a typical IRA might only earn a mere 1% to 2% annually. 
Self-Directed IRA Custodians
A custodian for a self-directed IRA is a third party organization. The U.S. tax code requires the custodial structure when people want to self-direct their investments. Although many custodians are available to the investing public, not all of them are prepared to handle real estate investing. 
How to Select a Custodian for Real Estate Transactions
Investors will have to search for custodial organizations that specifically allow for real estate investing. Upon finding prospective custodians in this category, an investor should ask specifically if a self-directed IRA can be set up to invest in a multifamily syndication.
The next consideration is whether the custodian will require documents to be executed in ink or if digital signatures are acceptable. Ideally, a custodian will also move funds electronically instead of with paper checks. These issues may matter due to the tight timelines on some investment opportunities. All investment paperwork must go through the custodian. This means investors must coordinate the paperwork between the real estate syndicate and the custodian. A custodian with a slow institutional process could struggle to meet all deadlines for committing to an investment. 
Real Estate Investing With a Solo 401(k)
Individuals and business owners have the option of establishing what is known as a solo 401(k). Unlike an employer-sponsored 401(k), a solo plan only has a single participant. An investor needs to find a 401(k) service provider that writes plans that specifically allow for investing in a multifamily syndicate. 
A very appealing feature of the solo 401(k) is that the plan participant controls the account. No custodian is necessary. The account holder creates an account to hold the plan's funds and can transfer funds from the plan as needed to make investments. The person saving for retirement signs all of the paperwork directly, which eliminates the hassle of working with a third-party custodian.  However, to prevent unexpected taxation, a person investing in real estate with a solo 401(k) must never mix personal funds outside of the retirement account in the transaction. 
Plan Ahead for Retirement Account Real Estate Investing
Investors cannot expect to supercharge retirement plan returns with real estate on a whim. Establishing a self-directed IRA or solo 401(k) could take up to eight weeks. Custodians and plan providers must be screened. Consultations with a tax accountant are needed to understand all issues before choosing a service provider. An investor must execute paperwork, set up an account, and pay necessary service provider fees. This timeline often will not accommodate the schedule for investing in a multifamily property. People interested in diversifying their retirement investing should have an appropriate account ready to go before exploring real estate deals. 
Although the upfront paperwork is substantial, the possibility of higher returns warrants the effort. Many people have significant funds in regular IRAs or 401(k) plans that they cannot use for real estate. With the right preparation, self-directed plans remove this restriction.
   https://www.ezfiuniversity.com/blogs/2021/2/28/what-to-expect-when-investing-in-syndications-with-alternative-retirement-plans
   https://themichaelblank.com/getting-started/how-to-invest-using-retirement-funds/